Study of Landing Technique during Visual Approach

24TH INTERNATIONAL CONGRESS OF THE AERONAUTICAL SCIENCES
STUDY OF LANDING TECHNIQUE
DURING VISUAL APPROACH
Hiroshi TAKAHARA*, Takashi KONDO*, Shinji SUZUKI**
*All Nippon Airways Co., LTD., **University of Tokyo
Keywords: Aircraft Operations
Abstract
The purpose of this paper is to focus on the
landing technique during the visual approach,
analyze the risk at landing and make instruction
to avoid the risk especially for unexperienced
pilots.
Airline has adopted several dozen of ab
initio pilots every year and they normally
become captains after flying about ten years as
co-pilot. It is necessary in co-pilot for airline to
make flight operations, maneuver technique and
circumstantial judgment acquire effectively.
This study picks up the various risks at
landing, analyzes the causes behind them using
the flight simulator then makes the technique to
avoid the risks. And we compared the landing
technique of unexperienced pilot with that of
experienced pilot by the analysis using Neural
Network method and found this method is
effective to the quantitative analysis of the part
which the pilot processes sensuously at landing.
1. Introduction
With technological innovation, automatic
landing and rollout is introduced into the civil
aviation and executed in line operations if
circumstance permits. However, all runways do
not enable auto-landing and most of landings
are made with manual operation of the pilot. In
manual landing, pilot controls the aircraft taking
into the aircraft conditions and estimating the
aircraft movement, based on the visual
information, aircraft controllability,
aerodynamic characteristics and his experience,
etc. These landing techniques are acquired
through training and actual operation spending
long period
We analyzed the landing techniques which
veteran pilots acquire through experience, then
evaluated those using B767 flight simulator. As
a result, we divided the landing technique into
three phases as follows and picked up
remarkable items in each phase.
・Stabilized approach from 500ft to 30ft
・Flare technique
・Landing technique in the severe situation
Furthermore, we compared the landing
technique of unexperienced pilot which that of
veteran pilot by the analysis using Neural
Network method.
2 Stabilized Approach from 500ft to 30ft
Smooth landing or not depends on the stability
of the aircraft from 500 ft to 30 ft before touch
down. The pilot decides the target approach
speed based on the aircraft weight, landing flap
and surface wind, then controls the aircraft on
the desired path. The pilot monitors the outside
view and the cockpit instruments, takes the
corrective action if the aircraft sifts from the
desired path. Followings are the key points to
stabilize the aircraft smoothly.
2.1 Pilot Eye Position
The pilot adjusts his seat position to keep his
eye position always same. This is because the
pilot usually recognizes the change of path with
the distance between glare shield and the
runway or the horizon. When eye position is
high, while insight of the runway becomes easy,
the change of path becomes difficult to
1
H.TAKAHARA, T. KONDO, S. SUZUKI
recognize. In addition, when eye position is low,
it becomes the opposite.
Fig. 1 View from Pilot
2.2 Initial Flight Path
The pilot knows the required the pitch angle and
thrust empirically to maintain desired path. In
order to stabilize the path the pilot keeps the
wing level, controls the desired pitch angle, sets
the thrust lever then turns the nose into the wind
direction to overlap the aircraft track with the
runway direction. After that, the pilot corrects
the track on the localizer course or the runway
centerline.
2.3 Setting of Trim
The aircraft stability increases by setting of
accurate trim. The pilot takes the stabilizer trim
at the half of expected trim first to prevent the
over trim, then adjusts the trim after attitude is
stabilized. Because there is time lag in operation
of the stabilizer trim, the pilot controls the trim
anticipating that time lag. In addition, the pilot
adjusts the trim periodically because the
required trim varies according to the change of
speed. As for rudder trim, the pilot checks the
trim stays at zero at the certain phase in descent.
2.4 Awareness of Path Change
When path is fixed, the distance between the
glare shield and the runway do not change
largely until low altitude. If the pilot pays
attention to the outside view other than the
runway, it is likely to recognize the change of
path by the change of relative position
relationship. In addition, the glide slope of ILS
or PAPI information is effective if available.
It is necessary to pay attention that the
displacement from the proper path differs
depending upon the aircraft position even if the
glide slope deviation in cockpit instrument or
PAPI information is same. The 1 dot deviation
of glide slope in instrument means 0.35 degrees
deviation from the proper path, for instance,
when the glide slope deviation in instrument
shows 1 dot below at 500ft descending 3 degree
path, the aircraft flies approximately 50ft below
the proper path, and at 100ft, the aircraft flies
10ft below the path. The displacement of 1 dot
deviation in instrument is approximately equal
to the 1/10 of aircraft altitude. In other words, as
the aircraft is descending and near to the runway,
the significance of 1 dot deviation in instrument
changes, it is necessary to take the corrective
control considering this.
When the aircraft is near to the runway, the
influence of the difference between the aiming
point and the setting position of glide slope
antenna or PAPI becomes remarkable. Because
of this, the pilot changes the visual cue, i.e.
runway marking, as the aircraft is near to the
runway.
2.5 Corrective Control
The pilot recognizes the deviation from the
proper path and the distance and time to the
runway and considers when and how much the
corrective control is required, then takes the
corrective control. In this corrective control, the
deviation of speed and path, thrust, sink rate at
each altitude are checked, it is possible to take
the next corrective control referring the previous
control and totally the control is smooth. In
addition, if the pilot grasps the appropriate time
required for the speed change after the thrust
controls and the altitude change during
approach descent, it is effective to thrust control.
The pilot finally checks the aircraft
configuration by monitoring the speed and
thrust when crossing the runway threshold. If
the aircraft has the enough energy at this point,
the flare will be stable.
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Study of Landing Technique during Visual Approach
3. Flare Technique
Even if the aircraft is stabilized to 30ft, the
aircraft may land hard or float as the timing of
flare, pitch up amount and its rate. In case of
cross wind condition, the higher flare technique
is required because it is necessary to control of
lateral direction.
Followings are the key points at flare.
3.1 Shift of Aiming Point
The flare that the sink rate at touch down is
zero is ideal but it is not realistic. The pilot
changes the flight path to shallower one slowly
by shifting the aiming point to the inner from
30ft. This is time, it is important to recognize
the change of pitch angle and flight path
utilizing the outside view and the automatic
altitude callout effectively. For instance, if it
excessively concentrates on the aiming point,
the visual information such as the extent of the
runway edges, angle and size of the touch down
zone marking and the horizon etc. is not utilized,
then it is difficult to do the stable flare.
3.2 Nose Down Moment at Flare
As the aircraft gets near to the runway, the
ground effect works in the aircraft. This
increases the lift of the wing and makes the nose
down moment. This moment negates the nose
up moment by pitch up control at flare, although
the pilot pulls the control column, the pitch
attitude does not increase from expectation. In
addition, the influence is not large, but nose
down moment works by reducing the thrust.
The pilot controls the column at flare
considering these effects.
3.3 Time Lag at Pitch Up
When the pilot pulls the column, the nose up
moment works on the aircraft first, then the sink
rate reduces. The time lag between the pitch
control and the change of aircraft attitude shows
in Fig.2.
Fig.2 Time Lag of Pitch Up Control and
Aircraft Attitude Change
3.4 Effect of Weight
When the approach speed changes with the
aircraft weight, sink rate, which means the
approaching rate to the runway, changes
(Table 1).
Wt Flap TAS Wi TCH PCH
nd [ft] [deg] Vert G
[klb]
[kt]
280 25 Vref+5 H 42
2.3
1.2
240 25 Vref+5 H 45
3
1.5
240 25 Vref+5 H 45
0.8
1.4
V/S TDP
ft/m [ft]
250 1485
300 2272
200 2014
A/S
280
280
240
240
400
600
750
500
140
144
128
135
25
25
25
25
Vref+5
Vref+10
Vref+5
T
T
T
T
47
46
42
44
5.2
4
3.2
4.1
1.8
2.1
2.5
1.6
758
893
724
704
Vref+10
TAS: Target Approach Speed, TCH: Threshold Crossing Height,
TDP: Touch down Point, A/S: Air Speed at Threshold
[kt]
148
136
136
Wind: H: 10kt Head Windshear below 100ft
T: 10kt Tail Windshear below 100ft
Table 1 Sink Rate VS Aircraft Weight
And altitude loss until reducing the sink rate
changes by the aircraft weight even with the
same flare operation (Table 2).
Wt
[klb]
240
280
Alt Loss [ft]
Flare to PCH up
10
20
Alt Loss [ft]
Flare to Stop Sink
20
45
Table 2 Altitude Loss during Flare
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H.TAKAHARA, T. KONDO, S. SUZUKI
3.5 Landing in Cross Wind Condition
In cross wind condition, the pilot takes the crab
angle that is the angle between the aircraft axis
and the traveling direction, equal to the cross
wind component and makes approach. There are
three method, the landing with crab angle, the
landing that the aircraft axis coincides with the
runway centerline (Wing Low) and the landing
combined both.
steppes on the rudder of the leeward and turns
the control wheel to direct the aircraft axis to the
runway centerline direction then adjusts the
aircraft track to the runway centerline. After
touch down, the axis is adjusted to the runway
direction slowly until the nose gear grounds.
This method is effective because it is easy to
control the aircraft when the aircraft energy is
lost suddenly encountered wind shear. The
sufficient training is required in order to control
the aileron and rudder appropriately.
3.6 Effect of Runway Slope
The runway normally has up or down slope.
When the flare is made with only visual
information, there are cases that the pilot
misunderstands the pitch up amount from
relative relationship with the runway surface. It
is necessary to pay attention to the runway that
large slope exists.
3.7 Analysis of Landing Technique using
Neural Network Method
Crab Landing
Wing Low Landing
Fig. 3 Landing Method
When with wing low landing the wind is even,
if the appropriate rudder with corresponding
bank is taken, the aircraft stabilizes in the state,
but when the gale and gust exist, it is difficult to
control the aircraft in stable state because the
required rudder and bank quantity changes.
As for crab landing, big yawing moment occurs
at touch down and it is not desirable from
viewpoint of comfort in case that runway
surface is dry.
For example of B767, WCA of the 10.5 degrees
with crab landing and bank angle of 5 degrees
with wing low landing is required under the
condition, airspeed of 140kt and cross wind of
25kt.
In our B767 operation, the wing low landing is
taken below approximately 15kt cross wind and
above that the method of combining wing low
and crab landing is taken. For instance, the pilot
It is difficult to analyze the process that pilot
control the aircraft after recognizing the
environmental conditions, therefore, instructor
pilot make an advise with sensuous expression
in new pilot training. We compared the landing
technique of unexperienced pilot with that of
experienced pilot by the analysis using Neural
Network method. Then, we could obtain the
result that the experienced pilot increase the
sensitivity for the change of pitch after flare, but
unexperienced pilot decrease the sensitivity
after flare. This analysis agrees with the pilot
comments after this test and it shows this tool is
effective to grasp the pilot operation objectively.
The detail result of this analysis using Neural
Network Method refers to the other paper [1]
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Study of Landing Technique during Visual Approach
4. Landing Technique Corresponding to
Environmental Factors
This section is the study when the operational
circumstance is severe such as sudden change of
the wind, low visibility and contaminated
runway etc. In those circumstances, there are
many cases that missed approach is the best way
rather than landing for the safety.
4.1 Avoidance of Tail Contact
The unexpected decrease of head wind or
increase of tail wind brings the decrease of
aircraft energy. If it tries to stop the sink rate in
this state with only the pitch up, the aircraft
touches down with high pitch angle. In addition,
when the speed brake is up remaining the
control force to control column after touch
down, the pitch attitude increased
approximately 2 degrees at maximum in 1.5
seconds. At this situation, the risk of tail contact
is high. It is important to control the pitch
attitude taking into account the wind change and
recognizing the allowable pitch attitude at
touchdown. In addition, the appropriate callout
for pitch attitude is effective.
4.2 Landing on Slippery Runway
In case that the road surface is slippery under
the cross wind, the directional control is
difficult at rollout because the frictional force of
the gear is small. Although the allowable cross
wind is changed according to the runway
condition, the directional control after the touch
down is difficult when the aircraft track differs
from the runway centerline just before touch
down. As a result of analysis using simulator on
slippery runway with cross wind, when the
aircraft track has faced to the leeward at touch
down, keeping the runway centerline is rather
difficult and some cases reached to the off
runway.
When the environment and the external factors
are worse, the stabilized approach especially
becomes important. The pilot recognizes the
situation that he is placed, analyses the
circumstance expected from the situation from
his knowledge and experience and takes the best
action. That is required to the pilot.
5. Conclusion
We investigated the landing technique during
visual approach and studied the avoidance of its
risk. Attendant upon the technological
innovation, it is presumed that in the distant
future, automation takes the place of pilot duties,
but it seems to be the key point how it keeps
taking in the part where the pilot controls based
on the estimate from the past experience to the
system.
Under the present circumstances, most of flight
lands with manual operation, this circumstance
is expected to continue for some time. The
landing techniques of the pilots slightly differ
depending upon the pilot individuals. The
contents that are reported here are portion of the
verification result, but those are expected to be
effective to the young pilot as a guideline to do
the stabilized approach and landing. Our group
made CD-ROM that summarized this study, has
used as the training tool.
References
[1] Suzuki, S., Sanematsu, Takahara, H.,
“Analysis of Human Pilot Maneuver Using Neural
Network Modeling”, 24th ICAS2004
5
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