Need and Requirements for Aircraft Weighing

The weight of an aircraft and its balance are extremely
important for operating an aircraft in a safe and efficient
manner. When a manufacturer designs an aircraft and
the Federal Aviation Administration (FAA) certifies
it, the specifications identify the aircraft’s maximum
weight and the limits within which it must balance.
The maximum allowable weight is based on the surface
area of the wing, and how much lift it will generate
at a safe and appropriate airspeed. If a small general
aviation airplane, for example, required a takeoff speed
of 200 miles per hour (mph) to generate enough lift to
support its weight, that would not be safe. Taking off
and landing at lower airspeeds is certainly safer than
doing so at higher speeds.
Where an aircraft balances is also a significant factor
in determining if the aircraft is safe to operate. An
aircraft that does not have good balance can exhibit
poor maneuverability and controllability, making it
difficult or impossible to fly. This could result in an
accident, causing damage to the aircraft and injury to
the people on board. Safety is the primary reason for
concern about an aircraft’s weight and balance.
A secondary reason for concern about weight and balance, but also a very important one, is the efficiency of
the aircraft. Improper loading reduces the efficiency of
an aircraft from the standpoint of ceiling, maneuverability, rate of climb, speed, and fuel consumption. If
an airplane is loaded in such a way that it is extremely
nose heavy, higher than normal forces will need to be
exerted at the tail to keep the airplane in level flight.
The higher than normal forces at the tail will create
additional drag, which will require additional engine
power and therefore additional fuel flow in order to
maintain airspeed.
The most efficient condition for an aircraft is to have
the point where it balances fall very close to, or perhaps
exactly at, the aircraft’s center of lift. If this were the
case, little or no flight control force would be needed
to keep the aircraft flying straight and level. In terms
of stability and safety, however, this perfectly balanced
condition might not be desirable. All of the factors
that affect aircraft safety and efficiency, in terms of
its weight and balance, are discussed in detail in this
chapter.
Need and Requirements for
Aircraft Weighing
Every aircraft type certificated by the FAA, before leaving the factory for delivery to its new owner, receives a
weight and balance report as part of its required aircraft
records. The weight and balance report identifies the
empty weight of the aircraft and the location at which
the aircraft balances, known as the center of gravity. If
the manufacturer chooses to do so, it can weigh every
aircraft it produces and issue the weight and balance
report based on that weighing. As an alternative, the
manufacturer is permitted to weigh an agreed upon
percentage of a particular model of aircraft produced,
perhaps 10 to 20 percent, and apply the average to all
the aircraft.
After the aircraft leaves the factory and is delivered
to its owner, the need or requirement for placing the
aircraft on scales and reweighing it varies depending
on the type of aircraft and how it is used. For a small
general aviation airplane being used privately, such
as a Cessna 172, there is no FAA requirement that it
be periodically reweighed. There is, however, an FAA
requirement that the airplane always have a current and
accurate weight and balance report. If the weight and
balance report for an aircraft is lost, the aircraft must
be weighed and a new report must be created. If the
airplane has new equipment installed, such as a radio or
a global positioning system, a new weight and balance
report must be created. If the installer of the equipment
wants to place the airplane on scales and weigh it after
the installation, that is a perfectly acceptable way of
creating the new report. If the installer knows the exact
weight and location of the new equipment, it is also
possible to create a new report by doing a series of
mathematical calculations.
4-1
Over a period of time, almost all aircraft have a
tendency to gain weight. Examples of how this can
happen include an airplane being repainted without
the old paint being removed, and the accumulation of
dirt, grease, and oil in parts of the aircraft that are not
easily accessible for cleaning. When new equipment
is installed, and its weight and location are mathematically accounted for, some miscellaneous weight might
be overlooked, such as wire and hardware. For this
reason, even if the FAA does not require it, it is a good
practice to periodically place an aircraft on scales and
confirm its actual empty weight and empty weight
center of gravity.
Some aircraft are required to be weighed and have
their center of gravity calculated on a periodic basis,
typically every 3 years. Examples of aircraft that fall
under this requirement are:
1. Air taxi and charter twin-engine airplanes operating
under Title 14 of the Code of Federal Regulations
(14 CFR) part 135, section (§)135.185(a).
2. Airplanes with a seating capacity of 20 or more
passengers or a maximum payload of 6,000
pounds or more, as identified in 14 CFR part
125, §125.91(b). This paragraph applies to most
airplanes operated by the airlines, both main line
and regional, and to many of the privately operated
business jets.
Weight and Balance Terminology
Datum
The datum is an imaginary vertical plane from which
all horizontal measurements are taken for balance
purposes, with the aircraft in level flight attitude. If
the datum was viewed on a drawing or photograph of
an aircraft, it would appear as a vertical line which is
perpendicular (90 degrees) to the aircraft’s horizontal
axis. For each aircraft make and model, the location
of all items is identified in reference to the datum. For
example, the fuel in a tank might be 60 inches (60")
behind the datum, and a radio on the flight deck might
be 90" forward of the datum.
There is no fixed rule for the location of the datum,
except that it must be a location that will not change
during the life of the aircraft. For example, it would
not be a good idea to have the datum be the tip of the
propeller spinner or the front edge of a seat, because
changing to a new design of spinner or moving the seat
would cause the datum to change. It might be located
at or near the nose of the aircraft, a specific number
of inches forward of the nose, at the engine firewall,
4-2
Datum ( leading edge of wing)
Negative arm
Positive arm
Center of lift
Figure 4-1. Datum location and its effect on
positive and negative arms.
at the center of the main rotor shaft of a helicopter,
or any place that can be imagined. The manufacturer
has the choice of locating the datum where it is most
convenient for measurement, equipment location, and
weight and balance computation. Figure 4-1 shows
an aircraft with the leading edge of the wing being
the datum.
The location of the datum is identified in the Aircraft
Specifications or Type Certificate Data Sheet. Aircraft
certified prior to 1958 fell under the Civil Aeronautics
Administration, and had their weight and balance
information contained in a document known as Aircraft
Specifications. Aircraft certified since 1958 fall under
the FAA and have their weight and balance information
contained in a document known as a Type Certificate
Data Sheet. The Aircraft Specifications typically
included the aircraft equipment list. For aircraft with
a Type Certificate Data Sheet, the equipment list is a
separate document.
Arm
The arm is the horizontal distance that a part of the
aircraft or a piece of equipment is located from the
datum. The arm’s distance is always given or measured
in inches, and, except for a location which might be
exactly on the datum, it is preceded by the algebraic
sign for positive (+) or negative (−). The positive sign
indicates an item is located aft of the datum and the
negative sign indicates an item is located forward of
the datum. If the manufacturer chooses a datum that
is at the most forward location on an aircraft (or some
distance forward of the aircraft), all the arms will be
positive numbers. Location of the datum at any other
point on the aircraft will result in some arms being positive numbers, or aft of the datum, and some arms being
negative numbers, or forward of the datum. Figure 4-1
shows an aircraft where the datum is the leading edge
of the wing. For this aircraft, any item (fuel, seat, radio,
and so forth) located forward of the wing leading edge
will have a negative arm, and any item located aft of
the wing leading edge will have a positive arm. If an
item was located exactly at the wing leading edge, its
arm would be zero, and mathematically it would not
matter whether its arm was considered to be positive
or negative.
The arm of each item is usually included in parentheses
immediately after the item’s name or weight in the
Aircraft Specifications, Type Certificate Data Sheet,
or equipment list for the aircraft. In a Type Certificate
Data Sheet, for example, the fuel quantity might be
identified as 150 gallons (gal) (+138) and the nose
baggage limit as 200 pounds (lb) (−55). These numbers
indicate that the fuel is located 138" aft of the datum
and the nose baggage is located 55" forward of the
datum. If the arm for a particular piece of equipment is
not known, its exact location must be accurately measured. When the arm for a piece of equipment is being
determined, the measurement is taken from the datum
to the piece of equipment’s own center of gravity.
Moment
A moment is the product of a weight multiplied by its
arm. The moment for a piece of equipment is in fact a
torque value, measured in units of inch-pounds (in-lb).
To obtain the moment of an item with respect to the
datum, multiply the weight of the item by its horizontal
distance from the datum. Likewise, the moment of an
item with respect to the center of gravity (CG) of an
aircraft can be computed by multiplying its weight by
the horizontal distance from the CG.
A 5 lb radio located 80" from the datum would have a
moment of 400 inch-pounds (in-lb) (5 lb × 8"). Whether
the value of 400 in-lb is preceded by a positive (+) or
negative (−) sign depends on whether the moment is
the result of a weight being removed or added and
its location in relation to the datum. This situation
is shown in Figure 4-2, where the moment ends up
being a positive number because the weight and arm
are both positive.
The algebraic sign of the moment, based on the datum
location and whether weight is being installed or
removed, would be as follows:
• Weight being added aft of the datum produces a
positive moment (+ weight, + arm).
Datum 40" forward
of the firewall
Radio (5 lb)
Arm = 80"
Center of lift
Moment = Weight (Arm)
= 5 lb (80")
= 400 inch-pounds
Figure 4-2. Moment of a radio located aft of the datum.
When dealing with positive and negative numbers,
remember that the product of like signs produces a
positive answer and the product of unlike signs produces a negative answer.
Center of Gravity
The center of gravity (CG) of an aircraft is a point
about which the nose heavy and tail heavy moments
are exactly equal in magnitude. It is the balance point
for the aircraft. An aircraft suspended from this point
would have no tendency to rotate in either a nose-up
or nose-down attitude. It is the point about which the
weight of an airplane or any object is concentrated.
Figure 4-3 shows a first class lever with the pivot point
(fulcrum) located at the center of gravity for the lever.
Even though the weights on either side of the fulcrum
are not equal, and the distances from each weight to the
fulcrum are not equal, the product of the weights and
arms (moments) are equal, and that is what produces
a balanced condition.
Maximum Weight
The maximum weight is the maximum authorized
weight of the aircraft and its contents, and is indicated
in the Aircraft Specifications or Type Certificate Data
Sheet. For many aircraft, there are variations to the
maximum allowable weight, depending on the purForce
Force
Distance = 90"
Distance = 70"
• Weight being added forward of the datum
produces a negative moment (+ weight, − arm).
• Weight being removed aft of the datum produces
a negative moment (− weight, + arm).
• Weight being removed forward of the datum
produces a positive moment (− weight, − arm)
Moment = 700 lb (90")
= 63,000 in-lb
Fulcrum and
center of gravity
Moment = 900 lb (70")
= 63,000 in-lb
Figure 4-3. Center of gravity and a first class lever.
4-3
pose and conditions under which the aircraft is to be
flown. For example, a certain aircraft may be allowed
a maximum gross weight of 2,750 lb when flown in
the normal category, but when flown in the utility category, which allows for limited aerobatics, the same
aircraft’s maximum allowable gross weight might only
be 2,175 lb. There are other variations when dealing
with the concept of maximum weight, as follows:
included in the value, so it generally involves only
aircraft certified prior to 1978. Standard empty weight
would be a value supplied by the aircraft manufacturer, and it would not include any optional equipment that might be installed in a particular aircraft.
For most people working in the aviation maintenance
field, the basic empty weight of the aircraft is the most
important one.
• Maximum Ramp Weight — the heaviest weight
to which an aircraft can be loaded while it is sitting
on the ground. This is sometimes referred to as
the maximum taxi weight.
Empty Weight Center of Gravity
The empty weight center of gravity for an aircraft is the
point at which it balances when it is in an empty weight
condition. The concepts of empty weight and center of
gravity were discussed earlier in this chapter, and now
they are being combined into a single concept.
• Maximum Takeoff Weight — the heaviest
weight an aircraft can have when it starts the
takeoff roll. The difference between this weight
and the maximum ramp weight would equal the
weight of the fuel that would be consumed prior
to takeoff.
• Maximum Landing Weight — the heaviest
weight an aircraft can have when it lands. For
large wide body commercial airplanes, it can be
100,000 lb less than maximum takeoff weight, or
even more.
• Maximum Zero Fuel Weight — the heaviest
weight an aircraft can be loaded to without having
any usable fuel in the fuel tanks. Any weight loaded
above this value must be in the form of fuel.
Empty Weight
The empty weight of an aircraft includes all operating equipment that has a fixed location and is actually
installed in the aircraft. It includes the weight of the
airframe, powerplant, required equipment, optional
or special equipment, fixed ballast, hydraulic fluid,
and residual fuel and oil. Residual fuel and oil are the
fluids that will not normally drain out because they are
trapped in the fuel lines, oil lines, and tanks. They must
be included in the aircraft’s empty weight. For most aircraft certified after 1978, the full capacity of the engine
oil system is also included in the empty weight. Information regarding residual fluids in aircraft systems that
must be included in the empty weight, and whether or
not full oil is included, will be indicated in the Aircraft
Specifications or Type Certificate Data Sheet.
Other terms that are sometimes used when describing
empty weight include basic empty weight, licensed
empty weight, and standard empty weight. The term
“basic empty weight” typically applies when the
full capacity of the engine oil system is included in
the value. The term “licensed empty weight” typically applies when only the weight of residual oil is
4-4
One of the most important reasons for weighing an aircraft is to determine its empty weight center of gravity.
All other weight and balance calculations, including
loading the aircraft for flight, performing an equipment
change calculation, and performing an adverse condition check, begin with knowing the empty weight and
empty weight center of gravity. This crucial information is part of what is contained in the aircraft weight
and balance report.
Useful Load
To determine the useful load of an aircraft, subtract
the empty weight from the maximum allowable gross
weight. For aircraft certificated in both normal and
utility categories, there may be two useful loads listed
in the aircraft weight and balance records. An aircraft
with an empty weight of 900 lb will have a useful load
of 850 lb, if the normal category maximum weight is
listed as 1,750 lb. When the aircraft is operated in the
utility category, the maximum gross weight may be
reduced to 1,500 lb, with a corresponding decrease in
the useful load to 600 lb. Some aircraft have the same
useful load regardless of the category in which they
are certificated.
The useful load consists of fuel, any other fluids that
are not part of empty weight, passengers, baggage,
pilot, copilot, and crewmembers. Whether or not the
weight of engine oil is considered to be a part of useful
load depends on when the aircraft was certified, and
can be determined by looking at the Aircraft Specifications or Type Certificate Data Sheet. The payload of
an aircraft is similar to the useful load, except it does
not include fuel.
A reduction in the weight of an item, where possible,
may be necessary to remain within the maximum
weight allowed for the category in which an aircraft
is operating. Determining the distribution of these
weights is called a weight check.
Minimum Fuel
There are times when an aircraft will have a weight and
balance calculation done, known as an extreme condition check. This is a pencil and paper check in which
the aircraft is loaded in as nose heavy or tail heavy a
condition as possible to see if the center of gravity will
be out of limits in that situation. In a forward adverse
check, for example, all useful load in front of the forward CG limit is loaded, and all useful load behind this
limit is left empty. An exception to leaving it empty
is the fuel tank. If the fuel tank is located behind the
forward CG limit, it cannot be left empty because the
aircraft cannot fly without fuel. In this case, an amount
of fuel is accounted for, which is known as minimum
fuel. Minimum fuel is typically that amount needed
for 30 minutes of flight at cruise power.
For a piston engine powered aircraft, minimum fuel
is calculated based on the METO (maximum except
take-off) horsepower of the engine. For each METO
horsepower of the engine, one-half pound of fuel is
used. This amount of fuel is based on the assumption
that the piston engine in cruise flight will burn 1 lb
of fuel per hour for each horsepower, or 1⁄2 lb for 30
minutes. The piston engines currently used in small
general aviation aircraft are actually more efficient than
that, but the standard for minimum fuel has remained
the same.
Minimum fuel is calculated as follows:
Minimum Fuel (pounds) =
Engine METO Horsepower ÷ 2
For example, if a forward adverse condition check was
being done on a piston engine powered twin, with each
engine having a METO horsepower of 500, the minimum fuel would be 250 lb (500 METO Hp ÷ 2).
For turbine engine powered aircraft, minimum fuel is
not based on engine horsepower. If an adverse condition check is being performed on a turbine engine
powered aircraft, the aircraft manufacturer would need
to supply information on minimum fuel.
Tare Weight
When aircraft are placed on scales and weighed, it
is sometimes necessary to use support equipment to
aid in the weighing process. For example, to weigh a
tail dragger airplane, it is necessary to raise the tail in
order to get the airplane level. To level the airplane,
a jack might be placed on the scale and used to raise
the tail. Unfortunately, the scale is now absorbing the
weight of the jack in addition to the weight of the
airplane. This extra weight is known as tare weight,
and must be subtracted from the scale reading. Other
examples of tare weight are wheel chocks placed on
the scales and ground locks left in place on retractable
landing gear.
Procedures for Weighing an Aircraft
General Concepts
The most important reason for weighing an aircraft
is to find out its empty weight (basic empty weight),
and to find out where it balances in the empty weight
condition. When an aircraft is to be flown, the pilot in
command must know what the loaded weight of the
aircraft is, and where its loaded center of gravity is. In
order for the loaded weight and center of gravity to be
calculated, the pilot or dispatcher handling the flight
must first know the empty weight and empty weight
center of gravity.
Earlier in this chapter it was identified that the center
of gravity for an object is the point about which the
nose heavy and tail heavy moments are equal. One
method that could be used to find this point would
involve lifting an object off the ground twice, first
suspending it from a point near the front, and on the
second lift suspending it from a point near the back.
With each lift, a perpendicular line (90 degrees) would
be drawn from the suspension point to the ground. The
two perpendicular lines would intersect somewhere in
the object, and the point of intersection would be the
center of gravity. This concept is shown in Figure 4-4,
where an irregular shaped object is suspended from
two different points. The perpendicular line from the
first suspension point is shown in red, and the new
Suspended from this
point first, with red line
dropping perpendicular
to the ground
Center of gravity
Second suspension, with
blue line dropping
perpendicular to the ground
Figure 4-4. Center of gravity determined by two
suspension points.
4-5
suspension point line is shown in blue. Where the red
and blue lines intersect is the center of gravity.
If an airplane were suspended from two points, one
at the nose and one at the tail, the perpendicular drop
lines would intersect at the center of gravity the same
way they do for the object in Figure 4-4. Suspending
an airplane from the ceiling by two hooks, however,
is clearly not realistic. Even if it could be done, determining where in the airplane the lines intersect would
not be possible.
A more realistic way to find the center of gravity for an
object, especially an airplane, is to place it on a minimum
of two scales and to calculate the moment value for each
scale reading. In Figure 4-5, there is a plank that is 200"
long, with the left end being the datum (zero arm), and
6 weights placed at various locations along the length of
the plank. The purpose of Figure 4-5 is to show how the
center of gravity can be calculated when the arms and
weights for an object are known.
To calculate the center of gravity for the object in
Figure 4-5, the moments for all the weights need to
be calculated and then summed, and the weights need
to be summed. In the four column table in Figure 4-6,
the item, weight, and arm are listed in the first three
columns, with the information coming from Figure
4-5. The moment value in the fourth column is the
50 lb
0"
30"
125 lb
60"
80 lb
50 lb
95" C.G. 125"
106.9"
product of the weight and arm. The weight and moment
columns are summed, with the center of gravity being
equal to the total moment divided by the total weight.
The arm column is not summed. The number appearing
at the bottom of that column is the center of gravity.
The calculation would be as shown in Figure 4-6.
For the calculation shown in Figure 4-6, the total
moment is 52,900 in-lb, and the total weight is 495 lb.
The center of gravity is calculated as follows:
Center of Gravity= Total Moment ÷ Total Weight
= 52,900 in-lb ÷ 495 lb
= 106.9" (106.87 rounded off to tenths)
An interesting characteristic exists for the problem presented in Figure 4-5, and the table showing the center
of gravity calculation. If the datum (zero arm) for the
object was in the middle of the 200" long plank, with
100" of negative arm to the left and 100" of positive
arm to the right, the solution would show the center
of gravity to be in the same location. The arm for the
center of gravity would not be the same number, but
its physical location would be the same. Figure 4-7 and
Figure 4-8 show the new calculation.
Center of Gravity =Total Moment ÷ Total Weight
=3,400 in-lb ÷ 495 lb
=6.9" (6.87 rounded off to tenths)
90 lb 100 lb
145"
170" 200"
–100"
Figure 4-5. Center of gravity for weights on a
plank, datum at one end.
Item
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
50 lb
125 lb
–70"
–40"
80 lb
C.G.
6.9"
–5" 0"
50 lb
25"
90 lb 100 lb
45"
70" 100"
Figure 4-7. Center of gravity for weights on a
plank, datum in the middle.
Item
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
50 pound weight
50
+30
1,500
50 pound weight
50
–70
–3,500
125 pound weight
125
+60
7,500
125 pound weight
125
–40
–5,000
80 pound weight
80
+95
7,600
80 pound weight
80
–5
–400
50 pound weight
50
+125
6,250
50 pound weight
50
+25
1,250
90 pound weight
90
+145
13,050
90 pound weight
90
+45
4,050
100 pound weight
100
+170
17,000
100 pound weight
100
+70
7,000
Total
495
+106.9
52,900
Total
495
+6.9
3,400
Figure 4-6. Center of gravity calculation for weights on a
plank with datum at one end.
4-6
Figure 4-8. Center of gravity calculation for weights on a
plank with datum in the middle.
In Figure 4-7, the center of gravity is 6.9" to the right
of the plank’s center. Even though the arm is not the
same number, in Figure 4-5 the center of gravity is also
6.9" to the right of center (CG location of 106.9 with the
center being 100). Because both problems are the same
in these two figures, except for the datum location, the
center of gravity must be the same.
The definition for center of gravity states that it is the
point about which all the moments are equal. We can
prove that the center of gravity for the object in Figure
4-7 is correct by showing that the total moments on
either side of this point are equal. Using 6.87 as the
CG location for slightly greater accuracy, instead of
the rounded off 6.9 number, the moments to the left of
the CG would be as shown in Figure 4-9.
The moments to the right of the CG, as shown in Figure
4-7, would be as shown in Figure 4-10.
Disregarding the slightly different decimal value,
the moment in both of the previous calculations is
10,651 in-lb. Showing that the moments are equal is
a good way of proving that the center of gravity has
been properly calculated.
Weight and Balance Data
In order to weigh an aircraft and calculate its empty
weight and empty weight center of gravity, a technician
must have access to weight and balance information
Item
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
50 pound weight
50
76.87
3,843.50
125 pound weight
125
46.87
5,858.75
80 pound weight
80
11.87
949.60
255
135.61
10,651.85
Total
Figure 4-9. Moments to the left of the center of gravity.
about the aircraft. Possible sources of weight and balance data are as follows:
• Aircraft Specifications — applies primarily to aircraft certified under the Civil Aeronautics Administration, when the specifications also included a
list of equipment with weights and arms.
• Aircraft Operating Limitations — supplied by
the aircraft manufacturer.
• Aircraft Flight Manual — supplied by the
aircraft manufacturer.
• Aircraft Weight and Balance Report — supplied
by the aircraft manufacturer when the aircraft is
new, and by the technician when an aircraft is
reweighed in the field.
• Aircraft Type Certificate Data Sheet — applies
primarily to aircraft certified under the FAA and
the Federal Aviation Regulations, where the
equipment list with weights and arms is a separate
document.
The document in Figure 4-11 is a Type Certificate
Data Sheet (TCDS) for a Piper twin-engine airplane
known as the Seneca (PA-34-200). The main headings
for the information typically contained in a TCDS
are included, but much of the information contained
under these headings has been removed if it did not
directly pertain to weight and balance. Information on
only one model of Seneca is shown, because to show
all the different models would make the document
excessively long. The portion of the TCDS that has
the most direct application to weight and balance is
highlighted in yellow.
Some of the important weight and balance information
found in a Type Certificate Data Sheet is as follows:
1. Center of gravity range
2. Maximum weight
3. Leveling means
4. Number of seats and location
Item
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
5. Baggage capacity
6. Fuel capacity
7. Datum location
50 pound weight
50
18.13
906.50
90 pound weight
90
38.13
3,431.70
8. Engine horsepower
100 pound weight
100
63.13
6,313.00
9. Oil capacity
Total
240
119.39
10,651.25
10. Amount of fuel in empty weight
11. Amount of oil in empty weight
Figure 4-10. Moments to the right of the center of gravity.
4-7
Department of Transportation
Federal Aviation Administration
Type Certificate Data Sheet No. A7so – Revision 14
PIPER
PA-34-200
PA-34-200T
PA-34-220T
June 1, 2001
This data sheet, which is a part of type certificate No. A7SO, prescribes conditions and limitations under which
the product for which the type certificate was issued meets the airworthiness requirements of the Federal
Aviation Regulations.
Type Certificate Holder:
The New Piper Aircraft, Inc.
2926 Piper Drive
Vero Beach, Florida 32960
I. Model PA-34-200 (Seneca), 7 PCLM (Normal Category), Approved 7 May 1971.
Engines
S/N 34-E4, 34-7250001 through 34-7250214:
1 Lycoming LIO-360-C1E6 with fuel injector,
Lycoming P/N LW-10409 or LW-12586 (right side); and
1 Lycoming IO-360-C1E6 with fuel injector,
Lycoming P/N LW-10409 or LW 12586 (left side).
S/N 34-7250215 through 34-7450220:
1 Lycoming LIO-360-C1E6 with fuel injector,
Lycoming P/N LW-12586 (right side); and
1 Lycoming IO-360-C1E6 with fuel injector,
Lycoming P/N LW-12586 (left side).
Fuel
100/130 minimum grade aviation gasoline
Engine Limits
For all operations, 2,700 RPM (200 hp)
Propeller and
Propeller Limits
Left Engine
1 Hartzell, Hub Model HC-C2YK-2 ( ) E, Blade Model C7666A-0;
1 Hartzell, Hub Model HC-C2YK-2 ( ) EU, Blade Model C7666A-0;
1 Hartzell, Hub Model HC-C2YK-2 ( ) EF, Blade Model FC7666A-0;
1 Hartzell, Hub Model HC-C2YK-2 ( ) EFU, Blade Model FC7666A-0;
1 Hartzell, Hub Model HC-C2YK-2CG (F), Blade Model (F) C7666A
(This model includes the Hartzell damper); or
1 Hartzell, Hub Model HC-C2YK-2CGU (F), Blade Model (F) C7666A
(This model includes the Hartzell damper).
Note: HC-( )2YK-( ) may be substituted for HC-( )2YR-( ) per Hartzell Service Advisory 61.
Right Engine
1 Hartzell, Hub Model HC-C2YK-2 ( ) LE, Blade Model JC7666A-0;
1 Hartzell, Hub Model HC-C2YK-2 ( ) LEU, Blade Model JC7666A-0;
1 Hartzell, Hub Model HC-C2YK-2 ( ) LEF, Blade Model FJC7666A-0;
1 Hartzell, Hub Model HC-C2YK-2 ( ) LEFU, Blade Model FJC7666A-0;
1 Hartzell, Hub Model HC-C2YK-2CLG (F), Blade Model (F) JC7666A
(This model includes the Hartzell damper); or
Figure 4-11. Type Certificate Data Sheet.
4-8
1 Hartzell, Hub Model HC-C2YK-2CLGU (F), Blade Model (F) JC7666A
(This model includes the Hartzell damper.)
Note: HC-( )2YK-( ) may be substituted for HC-( )2YR-( ) per Hartzell Service
Advisory 61.
Pitch setting: High 79° to 81°, Low 13.5° at 30" station.
Diameter: Not over 76", not under 74". No further reduction permitted.
Spinner: Piper P/N 96388 Spinner Assembly and P/N 96836 Cap Assembly, or
P/N 78359-0 Spinner Assembly and P/N 96836-2 Cap Assembly (See NOTE 4)
Governor Assembly:
1 Hartzell hydraulic governor, Model F-6-18AL (Right);
1 Hartzell hydraulic governor, Model F-6-18A (Left).
Avoid continuous operation between 2,200 and 2,400 RPM unless aircraft is
equipped with Hartzell propellers which incorporate a Hartzell damper on both left
and right engine as noted above.
Airspeed Limits
VNE (Never exceed)
VNO (Maximum structural cruise)
VA (Maneuvering, 4,200 lb)
VA (Maneuvering, 4,000 lb)
VA (Maneuvering, 2,743 lb)
VFE (Flaps extended)
VLO (Landing gear operating)
Extension
Retract
VLE (Landing gear extended)
VMC (Minimum control speed)
CG Range (Gear Extended)
S/N 34-E4, 34-7250001 through 34-7250214 (See NOTE 3):
(+86.4) to (+94.6) at 4,000 lb
(+82.0) to (+94.6) at 3,400 lb
(+80.7) to (+94.6) at 2,780 lb
S/N 34-7250215 through 34-7450220:
(+87.9) to (+94.6) at 4,200 lb
(+82.0) to (+94.6) at 3,400 lb
(+80.7) to (+94.6) at 2,780 lb
Straight line variation between points given.
Moment change due to gear retracting landing gear (-32 in-lb)
Empty Weight
CG Range
None
Maximum Weight
S/N 34-E4, 34-7250001 through 34-7250214:
4,000 lb – Takeoff
4,000 lb – Landing
See NOTE 3.
Maximum Weight
S/N 34-7250215 through 34-7450220:
4,200 lb – Takeoff
4,000 lb – Landing
No. of Seats
7 (2 at +85.5, 3 at +118.1, 2 at +155.7)
217 mph
190 mph
146 mph
146 mph
133 mph
125 mph
(188 knots)
(165 knots)
(127 knots)
(127 knots)
(115 knots)
(109 knots)
150 mph
125 mph
150 mph
80 mph
(130 knots)
(109 knots)
(130 knots)
(69 knots)
Maximum Baggage 200 lb (100 lb at +22.5, 100 lb at +178.7)
Figure 4-11. Type Certificate Data Sheet. (continued)
4-9
Fuel Capacity
98 gallons (2 wing tanks) at (+93.6) (93 gallons usable)
See NOTE 1 for data on system fuel.
Oil Capacity
8 qt per engine (6 qt per engine usable)
See NOTE 1 for data on system oil.
Control Surface
Movements
Rudder
Ailerons
(±2°)
Up 30°Down 15°
Stabilator
Up 12.5° (+0,-1°)Down 7.5° (±1°)
(±1°)
Left 35°
Right 35°
Stabilator Trim Tab
(±1°)
Down 10.5°Up 6.5°
(Stabilator neutral)
Wing Flaps
(±2°)
Up 0°Down 40°
Rudder Trim Tab
(±1°)
Left 17°Right 22°
(Rudder neutral)
Nosewheel
S/N 34-E4, 34-7250001 through 34-7350353:
Travel
(±1°)
Left 21°
Right 21°
Nosewheel
S/N 34-7450001 through 34-7450220:
Travel
(±1°)
Left 27°
Right 27°
Manufacturer's
Serial Numbers
3449001 and up.
Data Pertinent To All Models
Datum
78.4" forward of wing leading edge from the inboard edge of the inboard fuel tank.
Leveling Means
Two screws left side fuselage below window.
Certification Basis
Type Certificate No. A7SO issued May 7, 1971, obtained by the manufacturer
under the delegation option authorization. Date of Type Certificate application
July 23, 1968.
Model PA-34-200 (Seneca I):
14 CFR part 23 as amended by Amendment 23-6 effective August 1, 1967; 14 CFR part 23.959 as amended by Amendment 23-7 effective September 14, 1969;
and 14 CFR part 23.1557(c)(1) as amended by Amendment 23-18 effective May 2,
1977. Compliance with 14 CFR part 23.1419 as amended by Amendment 23-14
effective December 20, 1973, has been established with optional ice protection
provisions.
Production Basis
Production Certificate No. 206. Production Limitation Record issued and the
manufacturer is authorized to issue an airworthiness certificate under the delegation
option provisions of 14 CFR part 21.
Equipment
The basic required equipment as prescribed in the applicable airworthiness
regulations (see Certification Basis) must be installed in the aircraft for certification.
In addition, the following items of equipment are required:
Figure 4-11. Type Certificate Data Sheet. (continued)
4-10
Model
Afm/pohReport # Approved
PA-34-200(Seneca) AFM
VB-353
7/2/71
AFM
VB-423
5/20/72
AFM
VB-563
5/14/73
AFM Supp.
VB-588
7/20/73
AFM Supp.
VB-601
11/9/73
Serial Effectivity
34-E4, 34-7250001 through
34-7250214
34-7250001 through
34-7250189 when Piper Kit
760-607 is installed;
34-7250190 through
34-7250214 when Piper Kit
760-611 is installed; and
34-7250215 through
34-7350353
34-7450001 through
34-7450220
34-7250001 through
34-7450039 when propeller
with dampers are installed
34-7250001 through
34-745017 when ice protection system is installed
NOTES
NOTE 1
Current Weight and Balance Report, including list of equipment included in certificated
empty weight, and loading instructions when necessary, must be provided for each aircraft
at the time of original certification. The certificated empty weight and corresponding center
of gravity locations must include undrainable system oil (not included in oil capacity) and
unusable fuel as noted below:
Fuel: 30.0 lb at (+103.0) for PA-34 series, except Model PA-34-220T (Seneca V),
S/N 3449001 and up
Fuel: 36.0 lb at (+103.0) for Model PA-34-220T (Seneca V), S/N 3449001 and up
Oil:
6.2 lb at (+ 39.6) for Model PA-34-200
Oil:
12.0 lb at (+ 43.7) for Models PA-34-200T and PA-34-220T
NOTE 2
All placards required in the approved Airplane Flight Manual or Pilot’s Operating Handbook
and approved Airplane Flight Manual or Pilot’s Operating Handbook supplements must be
installed in the appropriate location.
NOTE 3
The Model PA-34-200; S/N 34-E4, 34-7250001 through 34-7250189, may be operated at a
maximum takeoff weight of 4,200 lb when Piper Kit 760-607 is installed. S/N 34-7250190
through 34-7250214 may be operated at a maximum takeoff weight of 4,200 lb when Piper
Kit 760-611 is installed.
NOTE 4
The Model PA-34-200; S/N 34-E4, 34-7250001 through 34-7250189, may be operated
without spinner domes or without spinner domes and rear bulkheads when Piper Kit 760-607
has been installed. ----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
NOTE 5
The Model PA-34-200 may be operated in known icing conditions when equipped with
spinner assembly and the following kits: ---------------------------------------------------------------
NOTE 6
Model PA-34-200T; S/N 34-7570001 through 34-8170092, may be operated in known icing
conditions when equipped with deicing equipment installed per Piper Drawing No. 37700 and
spinner assembly.
Figure 4-11. Type Certificate Data Sheet. (continued)
4-11
NOTE 7
The following serial numbers are not eligible for import certification to the United
States: ------------------------------------------------------------------------------------------------
NOTE 8
Model PA-34-200; S/N 34-E4, S/N 34-7250001 through 34-7450220, and Model PA-34-200T;
S/N 34-7570001 through 34-8170092, and Model PA-34-220T may be operated subject to the
limitations listed in the Airplane Flight Manual or Pilot’s Operating Handbook with rear cabin
and cargo door removed.
NOTE 9
In the following serial numbered aircraft, rear seat location is farther aft as shown and the
center seats may be removed and replaced by CLUB SEAT INSTALLATION, which has
a more aft CG location as shown in “No. of Seats,” above:PA-34-200T: S/N 34-7770001
through 34-8170092.
NOTE 10
These propellers are eligible on Teledyne Continental L/TSIO-360-E only.
NOTE 11
With Piper Kit 764-048V installed weights are as follows: 4,407 lb – Takeoff 4,342 lb Landing (All weight in excess of 4,000 lb must be fuel) Zero fuel weight may be increased to
a maximum of 4,077.7 lb when approved wing options are installed (See POH VB-1140).
NOTE 12
With Piper Kit 764-099V installed, weights are as follows: 4,430 lb - Ramp 4,407 lb Takeoff, Landing, and Zero Fuel (See POH VB-1150).
NOTE 13
With Piper Kit 766-203 installed, weights are as follows: 4,430 lb - Ramp 4,407 lb - Takeoff,
Landing and Zero Fuel (See POH VB-1259).
NOTE 14
With Piper Kit 766-283 installed, weights are as follows: 4,430 lb - Ramp 4,407 lb - Takeoff,
Landing and Zero Fuel (See POH VB-1558).
NOTE 15
With Piper Kit 766-608 installed, weights are as follows: 4,430 lb - Ramp 4,407 lb - Takeoff,
Landing and Zero Fuel (See POH VB-1620).
NOTE 16
With Piper Kit 766-632 installed, weights are as follows: 4,430 lb - Ramp 4,407 lb - Takeoff,
Landing and Zero Fuel (See POH VB-1649).
NOTE 17
The bolt and stack-up that connect the upper drag link to the nose gear trunnion are required
to be replaced every 500 hours’ time-in-service. -----------------------------------------------------------------------------------------------------------------------------------------------------------------------
Figure 4-11. Type Certificate Data Sheet. (continued)
4-12
Weight and Balance Equipment
Scales
Two types of scales are typically used to weigh aircraft:
those that operate mechanically with balance weights
or springs, and those that operate electronically with
what are called load cells. The balance weight type of
mechanical scale, known as a beam scale, is similar
to that found in a doctor’s office, in which a bar rises
up when weight is put on the scale. A sliding weight
is then moved along the bar until the bar is centered
between a top and bottom stop.
The sliding weight provides the capability to measure
up to 50 lb, and the cup holds fixed weights that come
in 50 lb equivalent units. As an example of this scale
in use, let’s say the nosewheel of a small airplane is
placed on the scale with an applied weight of 580 lb.
To find out what the applied weight is, a technician
would place 550 lb of equivalent weight in the cup,
and then slide the weight on the beam out to the 30 lb
point. The 580 lb applied by the nosewheel would now
be balanced by the 580 lb of equivalent weight, and
the end of the beam would be centered between the
top and bottom stop.
A mechanical scale based on springs is like the typical
bathroom scale. When weight is applied to the scale,
a spring compresses, which causes a wheel that displays the weight to rotate. It would be difficult to use
this type of scale to weigh anything other than a very
small aircraft, because these scales typically measure
only up to 300 lb. The accuracy of this type of scale
is also an issue.
Electronic scales that utilize load cells come in two
varieties: the platform type and the type that mounts
to the top of a jack. The platform type of electronic
scale sits on the ground, with the tire of the airplane
sitting on top of the platform. Built into the platform is
an electronic load cell, which senses the weight being
applied to it and generates a corresponding electrical
signal. Inside the load cell there is an electronic grid
that experiences a proportional change in electrical
resistance as the weight being applied to it increases.
An electrical cable runs from the platform scale to a
display unit, which interprets the resistance change
of the load cell and equates it to a specific number
of pounds. A digital readout on the display typically
shows the weight. In Figure 4-12, a Piper Archer is
being weighed using platform scales that incorporate
electronic load cells. In this case, the platform scales
are secured to the hangar floor and stay permanently
in place.
Figure 4-12. Weighing a Piper Archer using
electronic platform scales.
In Figure 4-13, a Mooney M20 airplane is being
weighed with portable electronic platform scales.
Notice in the picture of the Mooney that its nose tire
is deflated (close-up shown in the lower right corner of
the photo). This was done to get the airplane in a level
flight attitude. This type of scale is easy to transport
and can be powered by household current or by a battery contained in the display unit. The display unit for
these scales is shown in Figure 4-14.
The display unit for the portable scales is very simple
to operate. [Figure 4-14] In the lower left corner is the
power switch, and in the lower right is the switch for
selecting pounds or kilograms. The red, green, and
yellow knobs are potentiometers for zeroing the three
scales, and next to them are the on/off switches for
the scales. Before the weight of the airplane is placed
on the scales, each scale switch is turned on and the
potentiometer knob turned until the digital display
reads zero. In Figure 4-14, the nose scale is turned on
and the readout of 546 lb is for the Mooney airplane
in Figure 4-13. If all three scale switches are turned
on at the same time, the total weight of the airplane
will be displayed.
The second type of electronic scale utilizes a load cell
that attaches to the top of a jack. The top of the load
cell has a concave shape that matches up with the jack
pad on the aircraft, with the load cell absorbing all the
weight of the aircraft at each jacking point. Each load
cell has an electrical cable attached to it, which connects to the display unit that shows the weight being
absorbed by each load cell. An important advantage
of weighing an aircraft this way is that it allows the
technician to level the aircraft. An aircraft needs to
be in a flight level attitude when it is weighed. If an
aircraft is sitting on floor scales, the only way to level
the aircraft might be to deflate tires and landing gear
4-13
Figure 4-13. Mooney M20 being weighed with portable electronic platform scales.
struts. When an aircraft is weighed using load cells on
jacks, leveling the aircraft is easy by simply adjusting
the height with the jacks. Figure 4-15 shows a regional
jet on jacks with the load cells in place.
Spirit Level
Before an aircraft can be weighed and reliable readings obtained, it must be in a level flight attitude. One
method that can be used to check for a level condition is to use a spirit level, sometimes thought of as a
carpenter’s level, by placing it on or against a specified
place on the aircraft. Spirit levels consist of a vial full
of liquid, except for a small air bubble. When the air
bubble is centered between the two black lines, a level
condition is indicated.
Figure 4-14. Display unit showing nosewheel
weight for Mooney M20.
4-14
In Figure 4-16, a spirit level is being used on a Mooney
M20 to check for a flight level attitude. By looking in
the Type Certificate Data Sheet, it is determined that
the leveling means is two screws on the left side of
the airplane fuselage, in line with the trailing edge of
the wing.
Plumb Bob
A plumb bob is a heavy metal object, cylinder or
cone shape, with a sharp point at one end and a string
attached to the other end. If the string is attached to a
given point on an aircraft, and the plumb bob is allowed
to hang down so the tip just touches the ground, the
point where the tip touches will be perpendicular to
where the string is attached. An example of the use of
Figure 4-15. Airplane on jacks with load cells in use.
Figure 4-16. Spirit level being used on a Mooney M20.
Figure 4-17. Plumb bob dropped from a wing leading edge.
a plumb bob would be measuring the distance from an
aircraft’s datum to the center of the main landing gear
axle. If the leading edge of the wing was the datum, a
plumb bob could be dropped from the leading edge and
a chalk mark made on the hangar floor. The plumb bob
could also be dropped from the center of the axle on
the main landing gear, and a chalk mark made on the
floor. With a tape measure, the distance between the
two chalk marks could be determined, and the arm for
the main landing gear would be known. Plumb bobs can
also be used to level an aircraft, described on page 4-27
of the Helicopter Weight and Balance section of this
chapter. Figure 4-17 shows a plumb bob being dropped
from the leading edge of an aircraft wing.
of pounds per gallon. When placed in a flask with
fuel in it, the glass tube floats at a level dependent on
the density of the fuel. Where the fuel intersects the
markings on the side of the tube indicates the pounds
per gallon.
Hydrometer
When an aircraft is weighed with full fuel in the
tanks, the weight of the fuel must be accounted for
by mathematically subtracting it from the scale readings. To subtract it, its weight, arm, and moment must
be known. Although the standard weight for aviation
gasoline is 6.0 lb/gal and jet fuel is 6.7 lb/gal, these
values are not exact for all conditions. On a hot day
versus a cold day, these values can vary dramatically.
On a hot summer day in the state of Florida, aviation
gasoline checked with a hydrometer typically weighs
between 5.85 and 5.9 lb/gal. If 100 gallons of fuel
were involved in a calculation, using the actual weight
versus the standard weight would make a difference
of 10 to 15 lb.
When an aircraft is weighed with fuel in the tanks, the
weight of fuel per gallon should be checked with a
hydrometer. A hydrometer consists of a weighted glass
tube which is sealed, with a graduated set of markings
on the side of the tube. The graduated markings and
their corresponding number values represent units
Preparing an Aircraft for Weighing
Weighing an aircraft is a very important and exacting
phase of aircraft maintenance, and must be carried out
with accuracy and good workmanship. Thoughtful
preparation saves time and prevents mistakes.
To begin, assemble all the necessary equipment, such as:
1. Scales, hoisting equipment, jacks, and leveling
equipment.
2. Blocks, chocks, or sandbags for holding the
airplane on the scales.
3. Straightedge, spirit level, plumb bobs, chalk line,
and a measuring tape.
4. Applicable Aircraft Specifications and weight and
balance computation forms.
If possible, aircraft should be weighed in a closed building where there are no air currents to cause incorrect
scale readings. An outside weighing is permissible if
wind and moisture are negligible.
Fuel System
When weighing an aircraft to determine its empty
weight, only the weight of residual (unusable) fuel
should be included. To ensure that only residual fuel
is accounted for, the aircraft should be weighed in one
of the following three conditions.
1. Weigh the aircraft with absolutely no fuel in the
aircraft tanks or fuel lines. If an aircraft is weighed
4-15
in this condition, the technician can mathematically
add the proper amount of residual fuel to the
aircraft, and account for its arm and moment.
The proper amount of fuel can be determined
by looking at the Aircraft Specifications or Type
Certificate Data Sheet.
2. Weigh the aircraft with only residual fuel in the
tanks and lines.
3. Weigh the aircraft with the fuel tanks completely
full. If an aircraft is weighed in this condition,
the technician can mathematically subtract the
weight of usable fuel, and account for its arm and
moment. A hydrometer can be used to determine
the weight of each gallon of fuel, and the Aircraft
Specifications or Type Certificate Data Sheet can
be used to identify the fuel capacity. If an aircraft
is to be weighed with load cells attached to jacks,
the technician should check to make sure it is
permissible to jack the aircraft with the fuel tanks
full. It is possible that this may not be allowed
because of stresses that would be placed on the
aircraft.
Never weigh an aircraft with the fuel tanks partially
full, because it will be impossible to determine exactly
how much fuel to account for.
Oil System
For aircraft certified since 1978, full engine oil is typically included in an aircraft’s empty weight. This can
be confirmed by looking at the Type Certificate Data
Sheet. If full oil is to be included, the oil level needs to
be checked and the oil system serviced if it is less than
full. If the Aircraft Specifications or Type Certificate
Data Sheet specifies that only residual oil is part of
empty weight, this can be accommodated by one of
the following two methods.
1. Drain the engine oil system to the point that only
residual oil remains.
2. Check the engine oil quantity, and mathematically
subtract the weight of the oil that would leave
only the residual amount. The standard weight for
lubricating oil is 7.5 lb/gal (1.875 pounds per quart
(lb/qt)), so if 7 qt of oil needed to be removed,
the technician would subtract 13.125 lb at the
appropriate arm.
Miscellaneous Fluids
Unless otherwise noted in the Aircraft Specifications or
manufacturer’s instructions, hydraulic reservoirs and
systems should be filled, drinking and washing water
4-16
reservoirs and lavatory tanks should be drained, and
constant speed drive oil tanks should be filled.
Flight Controls
The position of such items as spoilers, slats, flaps,
and helicopter rotor systems is an important factor when weighing an aircraft. Always refer to the
manufacturer’s instructions for the proper position of
these items.
Other Considerations
Inspect the aircraft to see that all items included in the
certificated empty weight are installed in the proper
location. Remove items that are not regularly carried
in flight. Also look in the baggage compartments to
make sure they are empty. Replace all inspection
plates, oil and fuel tank caps, junction box covers,
cowling, doors, emergency exits, and other parts that
have been removed. All doors, windows, and sliding
canopies should be in their normal flight position.
Remove excessive dirt, oil, grease, and moisture from
the aircraft.
Some aircraft are not weighed with the wheels on the
scales, but are weighed with the scales placed either
at the jacking points or at special weighing points.
Regardless of what provisions are made for placing the
aircraft on the scales or jacks, be careful to prevent it
from falling or rolling off, thereby damaging the aircraft and equipment. When weighing an aircraft with
the wheels placed on the scales, release the brakes to
reduce the possibility of incorrect readings caused by
side loads on the scales.
All aircraft have leveling points or lugs, and care must
be taken to level the aircraft, especially along the longitudinal axis. With light, fixed-wing airplanes, the lateral
level is not as critical as it is with heavier airplanes.
However, a reasonable effort should be made to level
the light airplanes along the lateral axis. Helicopters
must be level longitudinally and laterally when they
are weighed. Accuracy in leveling all aircraft longitudinally cannot be overemphasized.
Weighing Points
When an aircraft is being weighed, the arms must be
known for the points where the weight of the aircraft is
being transferred to the scales. If a tricycle gear small
airplane has its three wheels sitting on floor scales,
the weight transfer to each scale happens through the
center of the axle for each wheel. If an airplane is
weighed while it is on jacks, the weight transfer happens through the center of the jack pad. For a helicopter
with skids for landing gear, determining the arm for the
weighing points can be difficult if the skids are sitting
directly on floor scales. The problem is that the skid
is in contact with the entire top portion of the scale,
and it is impossible to know exactly where the center
of weight transfer is occurring. In such a case, place
a piece of pipe between the skid and the scale, and
the center of the pipe will now be the known point of
weight transfer.
The arm for each of the weighing points is the distance
from the center of the weight transfer point to the
aircraft’s datum. If the arms are not known, based on
previous weighing of the aircraft or some other source
of data, they must be measured when the aircraft is
weighed. This involves dropping a plumb bob from
the center of each weighing point and from the aircraft
datum, and putting a chalk mark on the hangar floor
representing each point. The perpendicular distance
between the datum and each of the weighing points can
then be measured. In Figure 4-18, the distance from the
nosewheel centerline to the datum is being measured
on a Cessna 310 airplane. Notice the chalk lines on
the hangar floor, which came as a result of dropping
a plumb bob from the nosewheel axle centerline and
from the datum. The nosewheel sitting on an electronic
scale can be seen in the background.
Center of Gravity Range
The center of gravity range for an aircraft is the limits
within which the aircraft must balance. It is identified
as a forward most limit (arm) and an aft most limit
(arm). In the Type Certificate Data Sheet for the Piper
Seneca airplane, shown earlier in this chapter, the range
is given as follows:
CG Range: (Gear Extended)
S/N 34-E4, 34-7250001 through
34-7250214 (See NOTE 3):
(+86.4") to (+94.6") at 4,000 lb
(+82.0") to (+94.6") at 3,400 lb
(+80.7") to (+94.6") at 2,780 lb
Straight line variation between points given.
Moment change due to gear retracting
landing gear (–32 in-lb)
Because the Piper Seneca is a retractable gear airplane,
the specifications identify that the range applies when
the landing gear is extended, and that the airplane’s
total moment will be decreased by 32 when the gear
retracts. To know how much the center of gravity will
Figure 4-18. Measuring the nosewheel arm
on a Cessna 310.
change when the gear is retracted, the moment of 32
in-lb would need to be divided by the loaded weight
of the airplane. For example, if the airplane weighed
3,500 lb, the center of gravity would move forward
0.009" (32 ÷ 3500).
Based on the numbers given, up to a loaded weight of
2,780 lb, the forward CG limit is +80.7" and the aft CG
limit is +94.6". As the loaded weight of the airplane
increases to 3,400 lb and eventually to the maximum
of 4,000 lb, the forward CG limit moves aft. In other
words, as the loaded weight of the airplane increases,
the CG range gets smaller. The range gets smaller as a
result of the forward limit moving back, while the aft
limit stays in the same place.
The data sheet identifies that there is a straight line
variation between the points given. The points being
referred to are the forward and aft center of gravity limits. From a weight of 2,780 lb to a weight of 3,400 lb,
the forward limit moves from +80.7" to +82.0", and if
plotted on a graph, that change would form a straight
line. From 3,400 lb to 4,000 lb, the forward limit moves
from +82 to +86.4", again forming a straight line. Plotted on a graph, the CG limits would look like what is
shown in Figure 4-19. When graphically plotted, the
CG limits form what is known as the CG envelope.
In Figure 4-19, the red line represents the forward limit
up to a weight of 2,780 lb. The blue and green lines
represent the straight line variation that occurs for the
forward limit as the weight increases up to a maximum
of 4,000 lb. The yellow line represents the maximum
weight for the airplane, and the purple line represents
the aft limit.
4-17
4,200
4,100
4,000
3,900
3,800
86.4 at 4,000 lb
Weight (lb)
3,700
3,600
3,500
3,400
82 at 3,400 lb
3,200
Forward
Aft
3,000
CG limit
CG limit
2,900
2,800
80.7 at 2,780 lb
2,700
2,600
78 79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
Center of Gravity (in)
Figure 4-19. Center of gravity envelope for the Piper Seneca.
Empty Weight Center of Gravity Range
For some aircraft, a center of gravity range is given
for the aircraft in the empty weight condition. This
practice is not very common with airplanes, but is often
done for helicopters. This range would only be listed
for an airplane if it was very small and had limited
positions for people and fuel. If the empty weight CG
of an aircraft falls within the empty weight CG limits,
it is known that the loaded CG of the aircraft will be
within limits if standard loading is used. This information will be listed in the Aircraft Specifications or Type
Certificate Data Sheet, and if it does not apply, it will
be identified as “none.”
Operating Center of Gravity Range
All aircraft will have center of gravity limits identified
for the operational condition, with the aircraft loaded
and ready for flight. If an aircraft can operate in more
than one category, such as normal and utility, more than
one set of limits might be listed. As shown earlier for
the Piper Seneca airplane, the limits can change as the
weight of the aircraft increases. In order to legally fly,
the center of gravity for the aircraft must fall within
the CG limits.
Standard Weights Used for Aircraft Weight
and Balance
Unless the specific weight for an item is known, the
standard weights used in aircraft weight and balance
are as follows:
4-18
• Aviation gasoline
6 lb/gal
• Turbine fuel
6.7 lb/gal
• Lubricating oil
7.5 lb/gal
• Water
8.35 lb/gal
• Crew and passengers 170 lb per person
Example Weighing of an Airplane
In Figure 4-20, a tricycle gear airplane is being
weighed by using three floor scales. The specifications
on the airplane and the weighing specific data are as
follows:
• Aircraft Datum:
Leading edge of the wing
• Leveling Means: Two screws, left side of
fuselage below window
• Wheelbase: 100"
• Fuel Capacity:
30 gal aviation gasoline
at +95"
• Unusable Fuel: 6 lb at +98"
• Oil Capacity:
8 qt at –38"
• Note 1: Empty weight includes
unusable fuel and full oil
• Left Main Scale
Reading:
650 lb
• Right Main Scale
Reading: 640 lb
• Nose Scale Reading: 225 lb
Datum
Main wheel
centerline
Right scale reading
640 lb
70"
Left scale reading
650 lb
100"
Wheel base
Nose scale reading
225 lb
Chocks
Nose wheel centerline
Figure 4-20. Example airplane being weighed.
• Tare Weight:
5 lb chocks on left main
5 lb chocks on right main
2.5 lb chock on nose
• During Weighing:
Fuel tanks full and oil full
Hydrometer check on
fuel shows 5.9 lb/gal
By analyzing the data identified for the airplane being
weighed in Figure 4-20, the following needed information is determined.
• Because the airplane was weighed with the fuel
tanks full, the full weight of the fuel must be
subtracted and the unusable fuel added back in.
The weight of the fuel being subtracted is based
on the pounds per gallon determined by the
hydrometer check (5.9 lb/gal).
• Because wheel chocks are used to keep the
airplane from rolling off the scales, their weight
must be subtracted from the scale readings as tare
weight.
• Because the main wheel centerline is 70" behind
the datum, its arm is a +70".
• The arm for the nosewheel is the difference
between the wheelbase (100") and the distance
from the datum to the main wheel centerline (70").
Therefore, the arm for the nosewheel is −30".
To calculate the airplane’s empty weight and empty
weight center of gravity, a six column chart is used.
Figure 4-21 shows the calculation for the airplane in
Figure 4-20.
Item
Weight
(lb)
Tare
(lb)
Net Wt.
(lb)
Nose
225
–2.5
222.5
–30
–6,675
Left Main
650
–5
645
+70
45,150
Right Main
640
–5
635
+70
44,450
1,515
–12.5
1,502.5
Subtotal
Fuel Total
Arm
(inches)
Moment
(in-lb)
82,925
–177
+95
–16,815
Fuel Unuse
+6
+98
588
Oil
Full
+50.1
66,698
Total
1,331.5
Figure 4-21. Center of gravity calculation for airplane being weighed.
4-19
Based on the calculation shown in the chart, the center
of gravity is at +50.1", which means it is 50.1" aft of
the datum. This places the center of gravity forward
of the main landing gear, which must be the case for
a tricycle gear airplane. This number is the result of
dividing the total moment of 66,698 in-lb by the total
weight of 1,331.5 lb.
Loading an Aircraft for Flight
The ultimate test of whether or not there is a problem
with an airplane’s weight and balance is when it is
loaded and ready to fly. The only real importance of
an airplane’s empty weight and empty weight center
of gravity is how it affects the loaded weight and balance of the airplane, since an airplane doesn’t fly when
it is empty. The pilot in command is responsible for
the weight and balance of the loaded airplane, and he
or she makes the final decision on whether or not the
airplane is safe to fly.
Example Loading of an Airplane
As an example of an airplane being loaded for flight,
the Piper Seneca twin will be used. The Type Certificate Data Sheet for this airplane was shown earlier in
this chapter, and its center of gravity range and CG
envelope were also shown.
The information from the Type Certificate Data Sheet
that pertains to this example loading is as follows:
CG Range
(Gear Extended) S/N 34-7250215 through
34-7450220:
(+87.9") to (+94.6") at 4,200 lb
(+82.0") to (+94.6") at 3,400 lb
(+80.7") to (+94.6") at 2,780 lb
Straight line variation between
points given.
−32 in‑lb moment change due to
gear retracting landing gear
Empty Weight
CG Range
None
Maximum Weight
S/N 34-7250215 through
34-7450220:
4,200 lb — Takeoff
4,000 lb — Landing
No. of Seats
7 (2 at +85.5", 3 at +118.1",
2 at +155.7")
Maximum Baggage
200 lb (100 lb at +22.5,
100 lb at +178.7)
Fuel Capacity
98 gal (2 wing tanks) at (+93.6")
(93 gal usable). See NOTE 1 for
data on system fuel.
For the example loading of the airplane, the following
information applies:
• Airplane Serial Number:
34-7250816
• Airplane Empty Weight:
2,650 lb
• Airplane Empty Weight CG: +86.8"
For today’s flight, the following useful load items will
be included:
• 1 pilot at 180 lb at an arm of +85.5"
• 1 passenger at 160 lb at an arm of +118.1"
• 1 passenger at 210 lb at an arm of +118.1"
• 1 passenger at 190 lb at an arm of +118.1"
• 1 passenger at 205 lb at an arm of +155.7"
• 50 lb of baggage at +22.5"
• 100 lb of baggage at +178.7"
• 80 gal of fuel at +93.6"
To calculate the loaded weight and CG of this airplane,
a four column chart will be used, as shown in Figure
4-22.
Based on the information in the Type Certificate Data
Sheet, the maximum takeoff weight of this airplane
is 4,200 lb, and the aft-most CG limit is +94.6". The
loaded airplane in the chart above is 25 lb too heavy,
and the CG is 1.82" too far aft. To make the airplane
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
2,650
+86.80
230,020.0
Pilot
180
+85.50
15,390.0
Passenger
160
+118.10
18,896.0
Passenger
210
+118.10
24,801.0
Passenger
190
+118.10
22,439.0
Passenger
205
155.70
31,918.5
Baggage
50
+178.70
1,125.0
Baggage
100
+93.60
17,870.0
Fuel
480
11.87
44,928.0
4,255
+96.42
407,387.5
Item
Empty Weight
Total
Figure 4-22. Center of gravity calculation for Piper Seneca.
4-20
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
2,650
+86.8
230,020.0
Pilot
180
+85.5
15,390.0
Passenger
210
+85.5
17,955.0
Passenger
160
+118.1
24,801.0
Passenger
190
+118.1
22,439.0
Passenger
205
+118.1
24,210.5
Baggage
100
+22.5
2,250.0
Baggage
25
+178.7
4,467.5
480
93.6
44,928.0
4,200
+92.0
386,461.0
Item
Empty Weight
Fuel
Total
Figure 4-23. Center of gravity calculation for
Piper Seneca with weights shifted.
safe to fly, the load needs to be reduced by 25 lb and
some of the load needs to be shifted forward. For
example, the baggage can be reduced by 25 lb, and
a full 100 lb of it can be placed in the more forward
compartment. One passenger can be moved to the
forward seat next to the pilot, and the aft-most passenger can then be moved forward. If these changes
are made, the four column calculation will be as shown
in Figure 4-23.
With the changes made, the loaded weight is now at the
maximum allowable of 4,200 lb, and the CG has moved
forward 4.41". The airplane is now safe to fly.
Weight and Balance Extreme
Conditions
A weight and balance extreme condition check, sometimes called an adverse condition check, involves
loading the aircraft in as nose heavy or tail heavy a
condition as possible, and seeing if the center of gravity
falls outside the allowable limits. This check is done
with pencil and paper. In other words, the aircraft is
not actually loaded in an adverse way and an attempt
made to fly it.
On what is called a forward extreme condition check,
all useful load items in front of the forward CG limit
are loaded, and all useful load items behind the forward
CG limit are left empty. So if there are two seats and a
baggage compartment located in front of the forward
CG limit, two people weighing 170 lb each will be
put in the seats, and the maximum allowable baggage
will be put in the baggage compartment. Any seat or
baggage compartment located behind the forward CG
limit will be left empty. If the fuel is located behind
the forward CG limit, minimum fuel will be shown in
the tank. Minimum fuel is calculated by dividing the
engine’s METO horsepower by 2.
On an aft extreme condition check, all useful load
items behind the aft CG limit are loaded, and all useful
load items in front of the aft CG limit are left empty.
Even though the pilot’s seat will be located in front of
the aft CG limit, the pilot’s seat cannot be left empty.
If the fuel tank is located forward of the aft CG limit,
minimum fuel will be shown.
Example Forward and Aft Extreme
Condition Checks
Using the stick airplane in Figure 4-24 as an example,
adverse forward and aft checks will be calculated.
Some of the data for the airplane is shown in the figure,
such as seat, baggage, and fuel information. The center
of gravity limits are shown, with arrows pointing in
the direction where maximum and minimum weights
will be loaded. On the forward check, any useful
load item located in front of 89" will be loaded, and
anything behind that location will be left empty. On
the aft check, maximum weight will be added behind
99" and minimum weight in front of that location. For
either of the checks, if fuel is not located in a maximum
weight location, minimum fuel must be accounted for.
Notice that the front seats show a location of 82" to 88",
meaning they are adjustable fore and aft. In a forward
check, the pilot’s seat will be shown at 82", and in the
aft check it will be at 88". Additional specifications for
the airplane shown in Figure 4-24 are as follows:
• Airplane Empty Weight: 1,850 lb
• Empty Weight CG:
+92.45"
• CG Limits:
+89" to +99"
• Maximum Weight:
3,200 lb
• Fuel Capacity:
45 gal at +95"
(44 usable)
40 gal at +102"
(39 usable)
In evaluating the two extreme condition checks, the
following key points should be recognized.
• The total arm is the airplane center of gravity, and
is found by dividing the total moment by the total
weight.
• For the forward check, the only thing loaded
behind the forward limit was minimum fuel.
• For the forward check, the pilot and passenger
seats were shown at the forward position of 82".
4-21
2 at 82"– 88"
2 at 105"
375 HP
2 at 125"
100 lb at 140"
FUEL
FUEL
95"
102"
75 lb
at 60"
Maximum weight
Minimum weight
Forward limit 89"
Minimum weight
Aft limit 99"
Maximum weight
Figure 4-24. Example airplane for extreme condition checks.
• For the forward check, the CG was within limits,
so the airplane could be flown this way.
• For the aft check, the only thing loaded in front
of the aft limit was the pilot, at an arm of 88".
Extreme Condition Forward Check
Item
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
Empty Weight
1,850.0
+92.45
171,032.5
Pilot
170.0
+82.00
13,940.0
Passenger
170.0
+82.00
13,940.0
Baggage
Fuel
Total
75.0
+60.00
4,500.0
187.5
+95.00
17,812.5
2,452.5
+90.20
221,225.0
Extreme Condition Aft Check
Item
Empty Weight
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
1,850
+92.45
171,032.5
Pilot
170
+88.00
14,960.0
2 Passengers
340
+105.00
35,700.0
2 Passengers
340
+125.00
42,500.0
Baggage
100
+140.00
14,000.0
Fuel
234
+102.00
23,868.0
3,034
+99.60
302,060.5
Total
Figure 4-25. Center of gravity extreme condition checks.
4-22
• For the aft check, the fuel tank at 102" was filled,
which more than accounted for the required
minimum fuel.
• For the aft check, the CG was out of limits by 0.6",
so the airplane should not be flown this way.
Equipment Change and Aircraft
Alteration
When the equipment in an aircraft is changed, such as
the installation of a new radar system or ground proximity warning system, or the removal of a radio or seat,
the weight and balance of an aircraft will change. An
alteration performed on an aircraft, such as a cargo door
being installed or a reinforcing plate being attached to
the spar of a wing, will also change the weight and balance of an aircraft. Any time the equipment is changed
or an alteration is performed, the new empty weight and
empty weight center of gravity must be determined.
This can be accomplished by placing the aircraft on
scales and weighing it, or by mathematically calculating the new weight and balance. The mathematical
calculation is acceptable if the exact weight and arm of
all the changes are known.
Example Calculation After an Equipment Change
A small twin-engine airplane has some new equipment
installed, and some of its existing equipment removed.
The details of the equipment changes are as follows:
• The total arm is the airplane’s center of gravity,
and is found by dividing the total moment by the
total weight.
• Airplane Empty
Weight:
2,350 lb
• Airplane Empty
Weight CG:
+24.7"
• Airplane Datum:
Leading edge of the wing
• Radio Installed:
5.8 lb at an arm of –28"
• Global Positioning
System Installed:
7.3 lb at an arm of –26"
• Emergency Locater
Transmitter Installed: 2.8 lb at an arm of +105"
• Strobe Light
Removed:
1.4 lb at an arm of +75"
• Automatic Direction
Finder (ADF)
removed:
3 lb at an arm of –28"
• Seat Removed:
34 lb at an arm of +60"
To calculate the new empty weight and empty weight
center of gravity, a four column chart is used. The
calculation would be as shown in Figure 4-26.
In evaluating the weight and balance calculation shown
in Figure 4-26, the following key points should be
recognized.
• The weight of the equipment needs to be identified
with a plus or minus to signify whether it is being
installed or removed.
• The sign of the moment (plus or minus) is
determined by the signs of the weight and arm.
• The strobe and the ADF are both being removed
(negative weight), but only the strobe has a
negative moment. This is because the arm for
the ADF is also negative, and two negatives
multiplied together produce a positive result.
• The result of the equipment change is that the
airplane’s weight was reduced by 22.5 lb and the
center of gravity has moved forward 0.67".
The Use of Ballast
Ballast is used in an aircraft to attain the desired CG
balance, when the center of gravity is not within limits
or is not at the location desired by the operator. It is
usually located as far aft or as far forward as possible
to bring the CG within limits, while using a minimum
amount of weight. Ballast that is installed to compensate for the removal or installation of equipment items
and that is to remain in the aircraft for long periods is
called permanent ballast. It is generally lead bars or
plates bolted to the aircraft structure. It may be painted
red and placarded: PERMANENT BALLAST — DO
NOT REMOVE. The installation of permanent ballast
results in an increase in the aircraft empty weight, and
it reduces the useful load.
Temporary ballast, or removable ballast, is used to
meet certain loading conditions that may vary from
time to time. It generally takes the form of lead shot
bags, sand bags, or other weight items that are not permanently installed. Temporary ballast should be placarded: BALLAST, XX LB. REMOVAL REQUIRES
WEIGHT AND BALANCE CHECK. The baggage
compartment is usually the most convenient location
for temporary ballast.
Whenever permanent or temporary ballast is installed,
it must be placed in an approved location and secured
in an appropriate manner. If permanent ballast is being
bolted to the structure of the aircraft, the location must
be one that was previously approved and designed for
the installation, or it must be approved by the FAA
as a major alteration before the aircraft is returned to
service. When temporary ballast is placed in a baggage
compartment, it must be secured in a way that prevents
it from becoming a projectile if the aircraft encounters
turbulence or an unusual flight attitude.
Item
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
Empty Weight
2,350.0
+24.70
58,045.0
Radio Install
+5.8
−28.00
−162.4
GPS Install
+7.3
−26.00
−189.8
ELT Install
+2.8
+105.00
294.0
Strobe Remove
−1.4
+75.00
−105.0
ADF Remove
−3.0
−28.00
84.0
Seat Remove
−34.0
+60.00
−2,040.0
To calculate how much ballast is needed to bring the
center of gravity within limits, the following formula
is used.
2,327.5
24.03
55,925.8
Ballast Needed =
Total
Figure 4-26. Center of gravity calculation
after equipment change.
Loaded weight of aircraft (distance CG is out of limits)
Arm from ballast location to affected limit
4-23
Item
Empty Weight
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
1,850
+92.45
171,032.5
Pilot
170
+88.00
14,960.0
2 Passengers
340
+105.00
35,700.0
2 Passengers
340
+125.00
42,500.0
Baggage
100
+140.00
14,000.0
Fuel
234
+102.00
23,868.0
3,034
+99.60
302,060.5
Total
Figure 4-27. Extreme condition check.
Figure 4-24 on page 4-22 and Figure 4-27 show an aft
extreme condition check being performed on an airplane. In this previously shown example, the airplane’s
center of gravity was out of limits by 0.6". If there
were a need or a desire to fly the airplane loaded this
way, one way to make it possible would be the installation of temporary ballast in the front of the airplane.
The logical choice for placement of this ballast is the
forward baggage compartment.
The center of gravity for this airplane is 0.6" too far
aft. If the forward baggage compartment is used as a
temporary ballast location, the ballast calculation will
be as follows:
Ballast Needed =
Loaded weight of aircraft (distance CG is out of limits)
Arm from ballast location to affected limit
=
3,034 lb (0.6")
39"
= 46.68 lb
When ballast is calculated, the answer should always
be rounded up to the next higher whole pound, or in
this case, 47 lb of ballast would be used. To ensure the
ballast calculation is correct, the weight of the ballast
should be plugged back into the four column calculation and a new center of gravity calculated.
The aft limit for the airplane was 99", and the new CG
is at 98.96", which puts it within acceptable limits. The
new CG did not fall exactly at 99" because the amount
of needed ballast was rounded up to the next higher
whole pound. If the ballast could have been placed
farther forward, such as being bolted to the engine
firewall, less ballast would have been needed. That
is why ballast is always placed as far away from the
affected limit as possible.
In evaluating the ballast calculation shown above, the
following key points should be recognized.
• The loaded weight of the aircraft, as identified in
the formula, is what the airplane weighed when
the CG was out of limits.
• The distance the CG is out of limits is the difference
between the CG location and the CG limit, in this
case 99.6" minus 99".
• The affected limit identified in the formula is
the CG limit which has been exceeded. If the
CG is too far aft, it is the aft limit that has been
exceeded.
• The aft limit for this example airplane is 99",
and the ballast is being placed in the baggage
compartment at an arm of 60". The difference
between the two is 39", the quantity divided by
in the formula.
Viewed as a first class lever problem, Figure 4-29
shows what this ballast calculation would look like. A
ballast weight of 46.68 lb on the left side of the lever
multiplied by the arm of 39" (99 minus 60) would
equal the aircraft weight of 3,034 lb multiplied by the
distance the CG is out of limits, which is 0.6" (99.6
minus 99).
Ballast weight of
46.68 lb at an
arm of 60"
Distance from Aft limit to Ballast = 39"
Item
Loaded Weight
Ballast
Total
Weight
(lb)
Arm
(inches)
Moment
(in-lb)
3,034
+99.60
302,060.5
47
+60.00
2,820.0
3,081
+98.96
304,880.5
Aircraft weight of
3,034 lb at a
CG of of 99.6"
0.6"
Distance out
of limits
In order to balance at the aft limit of 99", the moment to the left of
the fulcrum must equal the moment to the right of the fulcrum. The
moment to the right is the weight of the airplane multiplied by 0.6".
The moment to the left is the ballast weight multiplied by 39".
Figure 4-29. Ballast calculation as a first class lever.
Figure 4-28. Ballast calculation.
4-24
and model aircraft at the time of original certification.
The graphs become a permanent part of the aircraft
records, and are typically found in the Airplane Flight
Manual or Pilot’s Operating Handbook (AFM/POH).
These graphs, used in conjunction with the empty
weight and empty weight CG data found in the weight
and balance report, allow the pilot to plot the CG for
the loaded aircraft.
Loading Graphs and CG Envelopes
The weight and balance computation system, commonly called the loading graph and CG envelope system, is an excellent and rapid method for determining
the CG location for various loading arrangements.
This method can be applied to any make and model
of aircraft, but is more often seen with small general
aviation aircraft.
The loading graph illustrated in Figure 4-30 is used to
determine the index number (moment value) of any
item or weight that may be involved in loading the
aircraft. To use this graph, find the point on the verti-
Aircraft manufacturers using this method of weight
and balance computation prepare graphs similar to
those shown in Figures 4-30 and 4-31 for each make
360
320
ge
r
er
ng
Fro
nt
Pa
ss
en
240
200
Fu
120
Re
el
Pil
o
t&
160
ar
sse
Pa
e
gag
Bag
80
40
0
Oil
−2
0
2
4
6
8
10
12
14
16
18
20
22
24
26
28
Moment Index (Moment /1,000)
Figure 4-30. Aircraft loading graph.
2,400
2,300
Normal Category
2,200
2,100
2,000
ate
go
r
y
1,900
yC
1,800
1,700
Ut
ilit
Load Aircraft Weight (lb)
Load Weight (lb)
280
1,600
1,500
50
55
60
65
70
75
80
85
90
95
100 105 110 115
Loaded Aircraft Moment/1,000 (in-lb)
Figure 4-31. CG envelope.
4-25
cal scale that represents the known weight. Project a
horizontal line to the point where it intersects the proper
diagonal weight line (i.e., pilot, copilot, baggage).
Where the horizontal line intersects the diagonal, project a vertical line downward to determine the loaded
moment (index number) for the weight being added.
for the aircraft in the Normal Category and one for the
aircraft in the Utility Category.
The loading graph and CG envelope shown in Figures
4-30 and 4-31 are for an airplane with the following
specifications and weight and balance data.
• Number of Seats:
After the moment for each item of weight has been
determined, all weights are added and all moments are
added. The total weight and moment is then plotted
on the CG envelope. [Figure 4-31] The total weight
is plotted on the vertical scale of the graph, with a
horizontal line projected out from that point. The total
moment is plotted on the horizontal scale of the graph,
with a vertical line projected up from that point. Where
the horizontal and vertical plot lines intersect on the
graph is the center of gravity for the loaded aircraft.
If the point where the plot lines intersect falls inside
the CG envelope, the aircraft CG is within limits. In
Figure 4-31, there are actually two CG envelopes, one
Item
Weight (lb)
Moment (in-lb)
1,400
53,900
Pilot
180
6,000
Front Passengers
140
4,500
Rear Passengers
210
15,000
Baggage
100
9,200
Fuel
228
10,800
Total
2,258
99,400
Aircraft Empty Wt.
4
• Fuel Capacity (Usable): 38 gal of Av Gas
• Oil Capacity:
8 qt (included in
empty weight)
• Baggage:
120 lb
• Empty Weight:
1,400 lb
• Empty Weight CG:
38.5"
• Empty Weight Moment: 53,900 in-lb
An example of loading the airplane for flight and calculating the total loaded weight and the total loaded
moment is shown in Figures 4-32 and 4-33. The use of
the loading graph to determine the moment for each of
the useful load items is shown in Figure 4-33. The color
used for each useful load item in Figure 4-32 matches
the color used for the plot on the loading graph.
The total loaded weight of the airplane is 2,258 pounds
and the total loaded moment is 99,400 in-lb. These two
numbers can now be plotted on the CG envelope to see
if the airplane is within CG limits. Figure 4-34 shows
the CG envelope, with the loaded weight and moment
of the airplane plotted. The CG location shown falls
&F
ron
tP
ass
en
g
er
Figure 4-32. Aircraft load chart.
360
320
240
200
ge
en
Pil
ot
Load Weight (lb)
280
Re
a
ass
rP
r
l
e
Fu
160
e
gag
Bag
120
80
40
0
Oil
−2
0
2
4
6
8
10
12
14
16
18
20
Moment Index (Moment/1,000)
Figure 4-33. Example plots on a loading graph.
4-26
22
24
26
28
2,400
Normal Category
2,200
CG Location
2,100
Forward Limit
ry
2,000
yC
ate
go
1,900
1,800
Ut
ilit
Load Aircraft Weight (lb)
2,300
1,700
Aft Limit
1,600
1,500
50
55
60
65
70
75
80
85
90
95
100 105 110 115
Loaded Aircraft Moment/1,000 (in-lb)
Figure 4-34. CG envelope example plot.
within the normal category envelope, so the airplane is
within CG limits for this category.
It is interesting to note that the lines that form the CG
envelope are actually graphic plots of the forward
and aft CG limits. In Figure 4-34, the red line is a
graphic plot of the forward limit, and the blue and green
lines are graphic plots of the aft limit for the two different
categories.
Helicopter Weight and Balance
General Concepts
All of the terminology and concepts that apply to
airplane weight and balance also apply generally to
helicopter weight and balance. There are some specific
differences, however, which need to be identified.
Most helicopters have a much more restricted CG range
than do airplanes. In some cases, this range is less than
3". The exact location and length of the CG range is
specified for each helicopter, and usually extends a
short distance fore and aft of the main rotor mast or
centered between the main rotors of a dual rotor system.
Whereas airplanes have a center of gravity range only
along the longitudinal axis, helicopters have both longitudinal and lateral center of gravity ranges. Because
the wings extend outward from the center of gravity,
airplanes tend to have a great deal of lateral stability.
A helicopter, on the other hand, acts like a pendulum,
with the weight of the helicopter hanging from the
main rotor shaft.
Ideally, the helicopter should have such perfect balance
that the fuselage remains horizontal while in a hover.
If the helicopter is too nose heavy or tail heavy while
it is hovering, the cyclic pitch control will be used to
keep the fuselage horizontal. If the CG location is too
extreme, it may not be possible to keep the fuselage
horizontal or maintain control of the helicopter.
Helicopter Weighing
When a helicopter is being weighed, the location of
both longitudinal and lateral weighing points must be
known to determine its empty weight and empty weight
CG. This is because helicopters have longitudinal and
lateral CG limits. As with the airplane, the longitudinal arms are measured from the datum, with locations
behind the datum being positive arms and locations in
front of the datum being negative arms. Laterally, the
arms are measured from the butt line, which is a line
from the nose to the tail running through the middle
of the helicopter. When facing forward, arms to the
right of the butt line are positive; to the left they are
negative.
Before a helicopter is weighed, it must be leveled longitudinally and laterally. This can be done with a spirit
level, but more often than not it is done with a plumb
bob. For example, the Bell JetRanger has a location
inside the aft cabin where a plumb can be attached, and
allowed to hang down to the cabin floor. On the cabin
floor is a plate bearing cross hairs, with the cross hairs
corresponding to the horizontal and lateral axis of the
helicopter. When the point of the plumb bob falls in the
middle of the cross hairs, the helicopter is level along
both axes. If the tip of the plumb bob falls forward of
this point, the nose of the helicopter is too low; if it falls
to the left of this point, the left side of the helicopter is
4-27
Forward Ballast Station
+13"
Leveling
plate
with cross
hairs
Plumb
Bob
Datum
Forward Jack Point
+55.16"
+25" and −25" Laterally
Leveling Plate
+117.7"
Aft Jack Point
+204.92"
e
Sid
ht
g
i
R
se
No
l
Tai
t
Lef
Sid
e
Aft Ballast Station
+377"
Figure 4-35. Bell JetRanger.
too low. In other words, the tip of the plumb bob will
always move toward the low point.
A Bell JetRanger helicopter is shown in Figure 4-35,
with the leveling plate depicted on the bottom right of
the figure. The helicopter has three jack pads, two at
the front and one in the back. To weigh this helicopter,
three jacks would be placed on floor scales, and the
helicopter would be raised off the hangar floor. To
level the helicopter, the jacks would be adjusted until
the plumb bob point falls exactly in the middle of the
cross hairs.
As an example of weighing a helicopter, consider
the Bell JetRanger in Figure 4-35, and the following
specifications and weighing data.
• Datum:
55.16" forward of the
front jack point centerline
• Leveling
Means:
Plumb line from ceiling left
rear cabin to index plate on
floor
• Longitudinal
CG Limits:
+106" to +111.4" at 3,200 lb
+106" to +112.1" at 3,000 lb
+106" to +112.4" at 2,900 lb
+106" to +113.4" at 2,600 lb
+106" to +114.2" at 2,350 lb
+106" to +114.2" at 2,100 lb
Straight line variation between points given
4-28
• Lateral CG
Limits:
2.3" left to 3.0" right at
longitudinal CG +106.0"
3.0" left to 4.0" right at
longitudinal CG +108" to
+114.2"
Straight line variation between points given
• Fuel and Oil:
Empty weight includes
unusable fuel and unusable oil
• Left Front
Scale Reading: 650 lb
• Left Front
Jack Point:
Longitudinal arm of +55.16"
Lateral arm of –25"
• Right Front
Scale Reading: 625 lb
• Right Front
Jack Point:
Longitudinal arm of +55.16"
Lateral arm of +25"
• Aft Scale
Reading: 710 lb
• Aft Jack
Point: Longitudinal arm of +204.92"
Lateral arm of 0.0"
• Notes:
The helicopter was weighed
with unusable fuel and oil.
Electronic scales were used,
which were zeroed with the
jacks in place, so no tare weight
needs to be accounted for.
Longitudinal CG Calculation
Item
Scale (lb)
Tare Wt. (lb)
Left Front
650
0
650
+55.16
35,854.0
Right Front
625
0
625
+55.16
34,475.0
Aft
710
0
710
+204.92
145,493.2
1,985
+108.73
215,822.2
Arm (inches)
Moment (in-lb)
Total
Nt. Wt. (lb)
1,985
Arm (inches)
Moment (in-lb)
Lateral CG Calculation
Item
Scale (lb)
Tare Wt. (lb)
Nt. Wt. (lb)
Left Front
650
0
650
−25
−16,250
Right Front
625
0
625
+25
+15,625
Aft
710
0
710
0
0
1,985
+.31
−625
Total
1,985
Figure 4-36. Center of gravity calculation for Bell JetRanger.
Using six column charts for the calculations, the empty
weight and the longitudinal and lateral center of gravity
for the helicopter would be as shown in Figure 4-36.
Based on the calculations in Figure 4-36, it has been
determined that the empty weight of the helicopter is
1,985 lb, the longitudinal CG is at +108.73", and the
lateral CG is at –0.31".
Weight and Balance —
Weight-Shift Control Aircraft and
Powered Parachutes
The terminology, theory, and concepts of weight and
balance that applies to airplanes also applies to weightshift aircraft and powered parachutes. Weight is still
weight, and the balance point is still the balance point.
There are, however, a few differences that need to be
discussed. Before reading about the specifics of weight
and balance on weight-shift control and powered parachute aircraft, be sure to read about their aerodynamic
characteristics in Chapter 3, Physics.
Weight-shift control aircraft and powered parachutes
do not fall under the same Code of Federal Regulations
that govern certified airplanes and helicopters and,
therefore, do not have Type Certificate Data Sheets or
the same type of FAA mandated weight and balance
reports. Weight and balance information and guidelines
are left to the individual owners and the companies
with which they work in acquiring this type of aircraft.
Overall, the industry that is supplying these aircraft is
regulating itself well, and the safety record is good for
those aircraft being operated by experienced pilots.
The FAA has recently (2005) accepted a new classification of aircraft, known as Light Sport Aircraft (LSA).
A new set of standards is being developed which will
have an impact on the weight-shift control and powered
parachute aircraft and how their weight and balance
is handled.
Weight-Shift Control Aircraft
Weight-shift control aircraft, commonly known by
the name “trikes,” have very few options for loading
because they have very few places to put useful load
items. Some trikes have only one seat and a fuel tank,
so the only variables for a flight are amount of fuel and
weight of the pilot. Some trikes have two seats and a
small storage bin, in addition to the fuel tank.
The most significant factor affecting the weight and
balance of a trike is the weight of the pilot; if the aircraft has two seats, the weight of the passenger must
be considered. The trike acts somewhat like a single
main rotor helicopter because the weight of the aircraft
is hanging like a pendulum under the wing. Figure
4-37 shows a two-place trike, in which the mast and
the nose strut come together slightly below the wing
attach point. When the trike is in flight, the weight of
the aircraft is hanging from the wing attach point. The
weight of the engine and fuel is behind this point, the
passenger is almost directly below this point, and the
pilot is forward of this point. The balance of the aircraft
is determined by how all these weights compare.
The wing attach point, with respect to the wing keel, is
an adjustable location. The attach point can be loosened
4-29
Figure 4-38. Wing attach point for a weight-shift aircraft.
Figure 4-37. Weight and balance for a weight-shift aircraft.
and moved slightly forward or slightly aft, depending
on the weight of the occupants. For example, if the
aircraft is flown by a heavy person, the attach point can
be moved a little farther aft, bringing the wing forward,
to compensate for the change in center of gravity.
Figure 4-38 shows a close-up of the wing attach point,
and the small amount of forward and aft movement
that is available.
Powered Parachutes
Powered parachutes have many of the same characteristics as weight-shift control aircraft when it comes to
weight and balance. They have the same limited loading, with only one or two seats and a fuel tank. They
also act like a pendulum, with the weight of the aircraft
hanging beneath the inflated wing (parachute).
Figure 4-39. Powered parachute structure
with wing attach points.
a large airplane. The jacks and scales will be larger, and
it may take more personnel to handle the equipment,
but the concepts and processes are the same.
Weight and Balance for Large
Airplanes
Built-In Electronic Weighing
One difference that may be found with large airplanes
is the incorporation of electronic load cells in the
aircraft’s landing gear. With this type of system, the
airplane is capable of weighing itself as it sits on the
tarmac. The load cells are built into the axles of the
landing gear, or the landing gear strut, and they work
in the same manner as load cells used with jacks. This
system is currently in use on the Boeing 747-400, Boeing 777, Boeing 787, McDonnell Douglas MD-11, and
the wide body Airbus airplanes like the A-330, A-340,
and A-380.
Weight and balance for large airplanes is almost identical to what it is for small airplanes, on a much larger
scale. If a technician can weigh a small airplane and
calculate its empty weight and empty weight center of
gravity, that same technician should be able to do it for
The Boeing 777, utilizes two independent systems that
provide information to the airplane’s flight management computer. If the two systems agree on the weight
and center of gravity of the airplane, the data being
provided are considered accurate and the airplane can
The point at which the inflated wing attaches to the
structure of the aircraft is adjustable to compensate for
pilots and passengers of varying weights. With a very
heavy pilot, the wing attach point would be moved
forward to prevent the aircraft from being too nose
heavy. Figure 4-39 illustrates the structure of a powered
parachute with the adjustable wing attach points.
4-30
be dispatched based on that information. The flight
crew has access to the information on the flight deck
by accessing the flight management computer and
bringing up the weight and balance page.
decreases toward the tip. In relation to the aerodynamics of the wing, the average length of the chord on
these tapered swept-back wings is known as the mean
aerodynamic chord (MAC).
Mean Aerodynamic Chord
On small airplanes and on all helicopters, the center of
gravity location is identified as being a specific number
of inches from the datum. The center of gravity range
is identified the same way. On larger airplanes, from
private business jets to large jumbo jets, the center of
gravity and its range are typically identified in relation to
the width of the wing.
On these larger airplanes, the CG is identified as being
at a location that is a specific percent of the mean aerodynamic chord (% MAC). For example, imagine that
the MAC on a particular airplane is 100", and the CG
falls 20" behind the leading edge of the MAC. That
means it falls one-fifth of the way back, or at 20% of
the MAC.
The width of the wing on an airplane is known as the
chord. If the leading edge and trailing edge of a wing
are parallel to each other, the chord of the wing is the
same along the wing’s length. Business jets and commercial transport airplanes have wings that are tapered
and that are swept back, so the width of their wings is
different along their entire length. The width is greatest
where the wing meets the fuselage and progressively
Figure 4-40 shows a large twin-engine commercial
transport airplane. The datum is forward of the nose of
the airplane, and all the arms shown in the figure are
being measured from that point. The center of gravity
for the airplane is shown as an arm measured in inches.
In the lower left corner of the figure, a cross section
of the wing is shown, with the same center of gravity
information being presented.
Center of gravity
945"
Datum
MAC 180"
Leading edge
of MAC 900"
LEMAC 900"
45"
Trailing edge of MAC
1,080"
CG at 945"
Chord line
MAC = 180"
Figure 4-40. Center of gravity location on a large commercial transport.
4-31
To convert the center of gravity location from inches
to a percent of MAC, for the airplane shown in Figure
4-40, the steps are as follows:
1. Identify the center of gravity location, in inches
from the datum.
2. Identify the leading edge of the MAC (LEMAC),
in inches from the datum.
3. Subtract LEMAC from the CG location.
4. Divide the difference by the length of the MAC.
5. Convert the result in decimals to a percentage by
multiplying by 100.
As a formula, the solution to solve for the percent of
MAC would be:
CG − LEMAC
Percent of MAC =
× 100
MAC
The result using the numbers shown in Figure 4-40
would be:
Percent of MAC =
CG − LEMAC
× 100
MAC
=
945 − 900
× 100
180
= 25%
If the center of gravity is known in percent of MAC,
and there is a need to know the CG location in inches
from the datum, the conversion would be done as
follows:
1. Convert the percent of MAC to a decimal by
dividing by 100.
2. Multiply the decimal by the length of the MAC.
3. Add this number to LEMAC.
As a formula, the solution to convert a percent of MAC
to an inch value would be:
CG in inches = MAC % ÷ 100 × MAC + LEMAC
4-32
For the airplane in Figure 4-40, if the CG was at 32.5%
of the MAC, the solution would be:
CG in inches = MAC % ÷ 100 × MAC + LEMAC
= 32.5 ÷ 100 × 180 + 900
= 958.5
Weight and Balance Records
When a technician gets involved with the weight and
balance of an aircraft, it almost always involves a calculation of the aircraft’s empty weight and empty weight
center of gravity. Only on rare occasions will the technician be involved in calculating extreme conditions,
how much ballast is needed, or the loaded weight and
balance of the aircraft. Calculating the empty weight
and empty weight CG might involve putting the aircraft
on scales and weighing it, or a pencil and paper exercise
after installing a new piece of equipment.
The FAA requires that a current and accurate empty
weight and empty weight center of gravity be known
for an aircraft. This information must be included in
the weight and balance report, which is a part of the
aircraft permanent records. The weight and balance
report must be in the aircraft when it is being flown.
There is no required format for this report, but Figure
4-41 is a good example of recording the data obtained
from weighing an aircraft. As it is currently laid out,
the form would accommodate either a tricycle gear or
tail dragger airplane. Depending on the gear type, either
the nose or the tail row would be used. If an airplane
is being weighed using jacks and load cells, or if a
helicopter is being weighed, the item names must be
changed to reflect the weight locations.
If an equipment change is being done on an aircraft, and
the new weight and balance is calculated mathematically instead of weighing the aircraft, the same type
of form shown in Figure 4-41 can be used. The only
change would be the use of a four column solution,
instead of six columns, and there would be no tare
weight or involvement with fuel and oil.
Aircraft Weight and Balance Report
Results of Aircraft Weighing
Make Serial # Model
N#
Datum Location
Leveling Means
Scale Arms:
Nose
Tail
Left Main
Right Main
Scale Weights: Nose
Tail
Left Main
Right Main
Tare Weights: Nose
Tail
Left Main
Right Main
Weight and Balance Calculation
Item
Scale (lb)
Tare Wt. (lb)
Net Wt. (lb)
Arm (inches)
Moment (in-lb)
Nose
Tail
Left Main
Right Main
Subtotal
Fuel
Oil
Misc.
Total
Aircraft Current Empty Weight:
Aircraft Current Empty Weight CG:
Aircraft Maximum Weight:
Aircraft Useful Load:
Computed By:
(print name)
(signature)
Certificate #:
(A&P, Repair Station, etc.)
Date:
Figure 4-41. Aircraft weight and balance report.
4-33
4-34
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