ITA n° 7
Incidents in Air Transport
Operations in Winter Conditions
N° 7
October 2007
The presence of snow on a runway during takeoff and landing, the need for de-icing
aeroplane before departure, are conditions that are infrequently encountered on French
airports. To maintain a level of safety equivalent to that obtained outside of these conditions,
all those involved must be willing to act as if these exceptional circumstances were part
of the routine. Crew actions are obviously crucial, as is the quality of ground assistance.
The following examples highlight certain characteristics of these operations.
Lateral excursion on slippery runway
This was the first aeroplane
to land after the reopening of
the runway.
(1)
(2)
The landing weight was
16.5 t.
Bureau d’Enquêtes et d’Analyses
pour la sécurité de l’aviation civile
Zone Sud
Bâtiment 153
200 rue de Paris
Aéroport du Bourget
93352 Le Bourget Cedex
FRANCE
Tél. : +33 1 49 92 72 00
Fax : +33 1 49 92 72 03
incidents@bea.aero
History of Flight
An Embraer 145 took off from Lyon for
Basel Mulhouse at night after a delay
due to cleaning snow from the aeroplane.
Twenty minutes after takeoff, the crew
was informed of a one-hour closure of
the destination aerodrome due to snow
clearance operations. When the airport was
reopened, the crew checked the landing
distance available (LDA). With transmitted
friction coefficients of 0.16, 0.14 and 0.14 (1),
the onboard documentation provided landing
performance consistent with the weight of
the aeroplane (2) . The stabilized approach
was performed with flaps 45 ° configuration
at a speed of 130 kt and touchdown was
normal. During deceleration, the plane
swerved slightly to the left. The Captain,
PF, corrected by first using the brakes and
then thrust reversers asymmetrically. The
aeroplane lurched to the right, which the
PF could not control by pushing left. The
aeroplane left the runway and rolled along
the grass for a distance of 250 metres. It
returned to the runway through an input on
the nosewheel steering control. The plane
reached its parking position autonomously
without suffering damage. The excursion
caused no damage on the ground.
Additional Information
Destination weather Conditions observed
two hours before departure: 5,000 metres
visibility, rain, temperature 0 ° C. Conditions
at the time of departure: wind 300 ° / 10 kt,
visibility 1,500 metres, mist, rain, temperature
0 ° C and dew point -1 ° C. The weather
dossier made available to the crew did not
contain a SNOWTAM. Two SNOWTAM were
issued after the departure of the aeroplane.
The first reported a depth of 5 mm of wet
snow and snow clearance in progress. The
second, issued at the time of the reopening
of the runway, announced wet snow and ice
to a depth of 5 mm, the braking coefficient
and snowfall causing wet snow to freeze on
the cold runway.
Analysis of the excursion
Analysis of the flight parameters showed that
there were no gusts of crosswind, that the
thrust reversers extended simultaneously
and that reverse thrust was not immediately
applied. The excursion seemed mainly due
to the surface being made very slippery
by the presence of wet snow. The faster
acceleration of the right engine at the
time of application of reverse thrust could
have triggered the initial deviation of the
aeroplane. Locking the steering to the left at
the time of the lurch to the right contributed
to the nose-wheels deviating. The crew tried
to counter the skid using asymmetric reverse
thrust. This technique, which is not described
in the operating manual, did not prevent the
excursion.
Evaluations of performance on slippery
runways
An aeroplane’s tyres’ adherence to the
runway is essential for the rotation of the
wheels on landing, braking and steering
control. Adhesion can be quantified or
assessed by one of three methods:
• a description of the runway surface (type
and depth of possible contaminant), based
on observations by aviation personnel on
the ground;
• the friction coefficient of the runway
(runway-μ) measured by a system mounted
on a ground vehicle. This measurement
determines the maximum braking slip and
corresponds to the slip point of the tyre;
• braking efficiency, evaluated by the pilot at
the time of landing and described as good,
fair or poor.
Only the last
evaluation takes
into
account
certain aeroplane
p a r a m e t e r s .
However,
this information is
not available the first
plane landing.
2
Freinage avion et coefficient de freinage
Résumé des méthodes

Freinage avion
calculé
Freinage
rapporté
Données du
constructeur
0. 4
Coefficient de
freinage de
l’avion
(calculé)
µ
avion
Sèche
0. 3
0. 2
0. 1
Bon
Moyen
Médiocre
0. 0

Description
de la piste
1. 0
Meilleur freinage
Sèche
Coefficient 0. 8
Mouillée
Neige sèche
de friction
de la piste 0. 6
Neige
compacte
(mesuré)
Neige mouillée
Slush
Glace
Glace mouillée
Source Boeing

Mesure du coefficient
de freinage
µ
piste
OACI
Bon
0. 4
Moyen
0. 2
Médiocre
0. 0
Plus mauvais
freinage
Measuring the friction
coefficient is carried
out when necessary
on each third of the
runway. In this case, it
is expressed digitally
or as a quantity. The
following table shows
the corresponding
ICAO coefficient as
defined for defining a
SNOWTAM:
Coefficient
(3)
The depth can be difficult to
measure, especially when water
is present.
(4)
WED : Water Equivalent Depth.
(5)
Only two types of
contaminants are available,
«Packed snow» and «Wet
ice» with two columns for
the latter type depending
on whether the friction
coefficient is greater (*) or
lower (**) 0.25.
incidents in Air Transport
Terme utilisé
0,40 et plus
Bon
Good
Entre 0,39 et 0,36
Moyen/Bon
Medium Good
Entre 0,35 et 0,30
Moyen
Medium
Entre 0,29 et 0,26
Moyen/
médiocre
Medium Poor
0,25 et en dessous
Médiocre
Poor
0,09 et en dessous
Douteux
Unreliable
In addition, manufacturers have different
methods for characterizing the braking of
their aeroplane. For Boeing, the calculation
of landing performance uses a braking
coefficient (plane-μ which can not be
directly compared to the runway-μ) based
on description of braking efficiency (good /
average / poor). The difference between the
runway-μ and plane-μ reflects the limits of
the efficiency of the braking system. Airbus
bases its calculations on the type and depth
of the contaminant (3) . For Embraer, the
presentation of performance is described
below.
Documentation available on board
The flight manual contains tables that
offer two ways to calculate limitations on a
contaminated runway. The first is based on
an equivalent water depth (4) and provides
limitations based on aeroplane landing
To obtain WED, multiply
theContaminant Depth
by the Contaminant
Specific Gravity.
weight and the runway distance available
The second determines the runway distance
required depending on the weight of the
aeroplane and the contamination of the
runway (5).
Lessons Learned
Difficulties on a contaminated runway are
not limited to braking capacity in relation to
the runway distance available. This event
shows others related to lateral control.
The use of asymmetric thrust reversers, a
non-specified procedure, without a doubt
contributed to the excursion.
Manufacturer’s data only deal with landing
performance. In this respect, crews are
faced with the difficulty of interpreting the
parameters describing the contamination
and their correlation with data provided by
the manufacturer. The different methods
used to describe the condition of a runway
use different scales. As it is not always
possible to establish an exact correlation
between the parameter that describes the
runway (or friction coefficient of condition of
the runway) and the braking capabilities of
the aeroplane and as there is no correlation
rule accepted as a standard in the industry,
it is up to operators to provide their aircrew
with a method to easily determine landing
conditions based on information transmitted
on the condition of the runway. Following this
incident, the airline, for example, amended
its operations manual to add the following
instruction:
« It is forbidden to take off and/or land with
a measured friction coefficient lower
or equal to 0.25 »
Takeoff after incomplete tailplane de-icing
History of Flight
An ATR 42 was making its first flight of the
day on a morning in March. Temperature was
close to 0 ° C and the dewpoint temperature
was - 1 ° C. Half an hour before the scheduled
departure time, moderate snow fell for
about ten minutes(6) and the crew decided
to de-ice the aeroplane. Passengers were
boarded. The operation was performed by
a support company ramp agent in about
fifteenminutes(7) while the crew in the cockpit,
kept the control column hard forward in
accordance with the de-icing procedure. The
equipment used was a cherry picker with a
tank filled with a heated mixture of fluid type
II and water. The truck was positioned at the
side of the plane between the trailing edge
of the wing and the tail.
The ground operations coordinator, in contact
with the ramp agent by walkie-talkie, relayed
the end of the operation to the crew from
the line station. The copilot noticed that
the leading edges of the wings were still
contaminated. He told the coordinator who
came himself to carry out the additional deicing, but only on the wings. After the end of
de-icing and before starting up, the crew did
not perform the specific procedure to test the
deflection of the flight controls.
At the holding point, during the usual flight
control tests the copilot, PF, found that the
elevator control was quite hard to manoeuvre.
He pointed this out to the Captain, who
did not feel the phenomenon. It was then
concluded that residues from de-icing were
the cause and that they would disappear with
the relative wind during the takeoff run.
Soon after the rotation, the aeroplane pitched
up significantly. The crew had to pitch down
in order to compensate in order to control
it. The maximum deflection of the trim was
reached and the crew still had to push the
elevator control. After several attempts, they
stabilized the aeroplane at FL 70 at 180 kt
and diverted to the alternate airport. The
aeroplane’s behaviour improved slightly. It
landed without any further problems.
Additional Information
Aerodynamic explanation of the phenomenon
The hinge moment of the elevator can be
affected by the presence of residual ice or
other contaminants on the tail. The boundary
layer at the rear of the profile is modified.
This can cause the elevator to pitch up.
To restore balance the aeroplane must be
pitched down. If contamination is significant,
the nose-down stop can be reached without
the hinge moment of the elevator being
cancelled and additional inputs to pitch down
the aeroplane must be made to reduce the
aeroplane’s attitude.
3
(6)
This was the only rainfall
before aeroplane departure.
(7)
This was the first time
that the agent had done
this.
De-icing procedures
An operator must define procedures to be
followed for de-icing or anti-icing on the
ground, and for checks on the condition of
the aeroplane after these operations. For this
purpose, instructions must be included in the
Operations Manual.
The procedures below are from separate
parts of the operator’s manual.
- avril 2005
n°n°
7 -3October
2007
In the General section are:
(8)
This phenomenon cannot
explain the sensation of effort
on the elevator control during
testing of this surface.
Responsibilities
The decision to perform de-icing and/
or anti-icing is the responsibility of the
Captain. (…) the assistance provider icing
and / or icing (Airline ramp assistants,
assistance company, CCI, others ...) is
responsible for:
- The correct execution of the treatment
and the result obtained,
- Training support staff
[...]
Visual and touch inspection checks on both
wings must be performed by the mechanic
or by the Captain in the absence of a
mechanic, in particular after application of
a treatment and before engine start-up [...]
Checks
Checks on the de-icing / ant-icing product
used is the responsibility of the person
undertaking the work (self-check) [...]
At the end of operations, a visual inspection
and touch check is performed by the
mechanic or by the Captain. This check
determines whether the treatment was
effective and if all critical aeroplane areas
are free of ice or snow before push-back
or taxiing [...]
After de-icing / anti-icing the crew ensures
the correct movement of all control
surfaces and repeats this check before the
aeroplane enters the runway [...]
4
In the “Usage” part of the Operations Manual,
there are other instructions concerning deicing:
(9)
These operations are
unusual, a simplified guide
may be useful to crews.
To ensure the best icing / anti-icing
possible for the horizontal stabilizer,
during any application of fluid, the control
column should be held firmly forward at
the stop [...]
After de-icing / anti-icing procedure, levels
of effort on the elevator that are greater
than normal may be encountered. These
levels of effort can be more than
twice those normally encountered. This
should not be interpreted as a blocking
of the elevator leading to an unnecessary
decision to abort takeoff after V1. Although
not systematic, this phenomenon must be
expected and called out again during the
pre-takeoff briefing each time a de-icing
/ anti-icing procedure has been applied.
This increase in efforts on the elevator is
strictly limited to the rotation phase (8) and
disappears after takeoff.
Assistance providers
Each provider is responsible for staff training.
An annual audit is performed by the quality
assurance manager of the airline that uses
this service. In the case under consideration,
the agents that might perform de-icing / antiicing procedures received training, at the end
of which they were overall given authorisation
for initiation, implementation and checking
these operations. The training, which lasted
for a day, was purely theoretical. No practical
training was planned.
Lessons Learned
Some uncertainties remain about procedures
used for de-icing. The ramp agent conducted
the operation for the first time without having
received training. That was why it was not
easy for him to see that the operation had
not been correctly completed. Since that
time, the assistance company has set up
practical training for its agents. The visual
and touch check after de-icing planned by
the operator was not performed. On the one
hand, the mechanic was not present. On
the other hand, if this check should have
been performed by a pilot, he must put on a
harness to climb into the cherry picker and
this is impractical during departure. It was
found that the procedures to ensure checks
are not appropriate in all situations that may
be encountered at a stopover. In addition,
the procedures for de-icing / anti-icing on the
ground are in two different manuals (9), which
may explain why a part of the procedure was
not applied, specifically the checks on the
controls after the de-icing.
Accumulation of melted snow on landing gear on takeoff
Histoy of Flight
Un Fokker 70 décolle de Lille de nuit, aux
A Fokker 70 took off from Lille at night,
at around 18 h 00, in the snow. A runway
inspection that had been conducted shortly
before had determined that braking was good
and this information was passed to the crew.
Incidents in Air Transport
They found it difficult to control during thrust
application and asked the tower, after takeoff,
when the runway would be treated. During
the approach to the destination airport, while
the aeroplane was at 2,000 feet, the crew
ordered landing gear extension. The LG
MAIN UNSAFE display appeared and the
lights indicating nose and left main LG lock
down did not illuminate. The Captain decided
to abort the approach. The aeroplane was
vectored to holding to allow the problem to
be handled.
The crew made several landing gear extension
commands, normal and emergency, without
success.
The Captain, after informing the controller
decided to make a few high bank-angle
turns to try to lock down the landing gear by
gravity. These attempts were unsuccessful.
Shortly afterwards, the nose gear locked
down locked. The crew applied the «landing
with abnormal landing gear configuration»
procedure and declared an emergency. The
controller requested a delay in order to put
in place the emergency services. Meanwhile,
the Captain asked the cabin crew to prepare
the cabin. The aeroplane was vectored
to final approach and cleared for landing.
Descending through 1,200 ft, the left gear
lockdown light came on and the transition
light turned off. The plane landed and was
towed to the ramp.
Additional Information
Cause of the non-locking gear
The axis of the left main landing gear lock
hydraulic actuator was found broken. This
was due to an overload compression failure.
Immediately after landing, a significant
amount of ice was found around the different
parts up the landing gear.
Broken part of actuator
Failure profile
Communications on the meteorological
situation
We a t h e r i n f o r m a t i o n a t L i l l e L e s q u i n
indicated: between 14 h 40 and 15 h 05, rain
and sleet; between 15 h 05 and 15 h 27,
continuous rain; between 15 h 27 and 16 h
26 intermittent rain; between 16 h 26 and
17 h 36 rain and sleet; between 17 h 36 and
19 h 30, snow. The content of the ATIS was
as follows:
«Information Oscar recorded 17 h 24 active
runway 26, runway wet, wind 250 ° / 7 knots,
visibility 7 km, overcast, FEW 2000 ft BKN
000ft 5, temperature 0 ° C, dew point -1 ° C
«. The following ATIS recorded at takeoff,
stated: «Information Quebec
recorded at 17 h 59 active runway 26,
runway wet, wind 270 ° / 8 kt, visibility 4 km,
moderate snow showers, FEW 300 ft, 5000 ft
BKN, temperature 0 ° C, dew point - 1 ° C. ‘
Operations at Lille
During the previous rotation, after landing
at Lille at 16 h 35, the Fokker 70 crew
reported to the controller, at his request, that
snow was beginning to stick on the runway.
At 16 h 38, the Tower chief contacted the
meteorological service to know whether the
snow would last. The latter believed that the
snow would melt and stopp within one hour.
At 16 h 57, the snowfall was increasing, the
agent’s office called the Tower chief to know
whether a friction coefficient measurement
was required. The aeroplane that had landed
previously reported that braking was good. At
17 h 00, a plane landed. The crew reported
that snow hindered visibility severely on short
final though they were told that the snow was
light. Braking was still good.
At 17 h 08, the agent’s office again asked for
the runway friction coefficient measurement.
The Tower chief, who noticed that the snow
was beginning to settle on parking area,
requested an inspection of the runway. At
17 h 14, an aeroplane ready for departure
declined the proposal made by ATC for a
runway friction coefficient measurement to
be made before takeoff.
At 17 h 23, the runway friction coefficient
measurement was completed. The braking
coefficient was 0.56. The information
transmitted to the various crews that
requested it was that «braking is good.»
No mention was made of the presence of
melting snow. At 17 h 32, the Tower chief
again contacted the meteorological services
to know how long the snowfall would last.
They told him that it might last several hours
and a thickness of 3 to 6 cm snow soil was
announced.
At 17 h 34, the LOCALIZER broke down.
Snow on the antenna was doubtless the
cause. The ceiling was 300 ft and this made
it impossible for any more planes to land
in these conditions. At 17 h 46, the Fokker
70 asked for pushback. At 18 h 06, the
ramp services contacted the Tower for the
result of the last runway inspection. The
agent that responded did not conduct the
inspection himself but he stated that a film
of a centimetre of «slush» was observed. A
runway treatment was referred to but this was
delayed due to continuing snowfall.
5
Inspections of runways and SNOWTAM
Contrary to the runway inspection at 17 h
23, that at 19 h 40 mentioned the presence
of slush and a braking coefficient of 0.52.
A SNOWTAM was published at 20 h 00
indicating wet snow over the entire runway.
n° 7 - October 2007
Other aeroplanes affected
Another airplane of the same type, having
departed shortly afterwards, met with the
same difficulties when trying to extend the
landing gear. Melting snow accumulated
on the landing gear during the takeoff run
and acceleration had frozen during the
climb and cruise. At the time the gear was
extended, the nose gear lockdown indicator
light remained off. The crew applied the
associated procedure and managed to lock
down the landing gear. On the ground, no
failure was found in the system. It appears
that the incident was due to a landing gear
sensor being blocked by ice.
Organization of runway inspections
In France, the organization of runway
inspections can depend on various agencies
(State or management). The 15 March 2002
decree defines the conditions under which
manual inspections must be performed... »
6
Inspections of the movement area of the
aerodrome consist, among other things, of:
- Collecting information on the overall
condition of the area;
- Undertaking, as necessary, immediate
corrective actions
- Reporting to the authority in charge of air
traffic services, to air traffic control and /
or the management.
[...] Checks in the context of inspections
shall include the presence of snow,
snow drifts, ice, melting ice. When the
aerodrome receives at least one scheduled
commercial airline, at least two daily
inspections are to be performed. Additional
inspections may be required depending
on the circumstances, including special
weather phenomena: snow, ice... »
A report is to be made by radio to air traffic
services and actions and observations of the
inspection team recorded. Training of agents
who are responsible for
inspections is the responsibility of the agency
responsible for administering the aerodrome.
Lessons learned
The report made after an inspection on
a snowy runway can take many forms:
transmission of a runway friction coefficient,
d e s c r i b i n g t h e s t a t e o f t h e r u n w a y,
transmitting a SNOWTAM. In this case, the
agent who measured the friction obtained
a gross value of 0.56, which he converted
to «braking good ». From this result, it
was not considered useful to report the
presence of slush. If the knowledge of the
braking coefficient is in fact an essential
element, specifically for takeoff performance
purposes, the runway inspection should not
limit itself to supplying this parameter. The
manual on inspections makes it clear that all
information concerning the presence of snow
or slush must be provided. The study of this
event by the airport quality assurance team
made effective feedback possible.
The impact of contamination on the ground
on aeroplane systems is
often underestimated compared to
performance. In addition, the radio and
telephone communications used during this
investigation brought to light differences of
opinion on the rapidly changing meteorological
conditions between the various people
involved.
Finally, the manufacturer recommended
slightly delaying retraction of the landing gear
after takeoff from a contaminated runway to
remove any snow or ice, which the crew did
not think of doing, probably because they
were surprised by the condition of the runway
on takeoff.
Overrun on a snowy runway
(10)
The PF said after the
event that the first one
hundred and fifty metres
deceleration was correct,
then the runway became
very slippery and braking
practically impossible
Incidents in Air Transport
History of Flight
A Learjet 35 took off in the early evening
from Vienna (Austria) to Chambery, which
the crew estimated they would reach in two
hours. The Captain was PF. Lyon SaintExupéry was diversion aerodrome.
Meteorological information was collected
by the crew at Vienna, then information
received in flight made it possible to land at
Chambéry. The crew, under radar vectoring,
intercepted ILS 18 and continued the
approach. The controller cleared them for
landing and transmitted «runway wet and
braking action good «. The aeroplane landed
at the reference speed of 127 knots.
The aeroplane touched down at the markings.
It began to decelerate, then skidded (10). The
PF succeeded in keeping to the runway
centreline. The controller saw the plane at
a speed that he estimated to be too high to
allow the aeroplane to exit the runway before
the south taxiway. He then asked the crew to
make a U-turn at the end of the runway and
backtrack to reach the parking area. Braking
became effective again at the turn-around
area, but the aeroplane overran the runway
end by a distance of about fifteen metres.
The crew announced a runway excursion.
The controller, who did not see it, due to the
dark, triggered the alert.
Additional Information
Characteristics of the runway
The aerodrome, located at an altitude of 779
ft, has a runway 18/36 that is 2,020 metres
long. The Runway 18 LDA was 1,790 metres.
The slope of the ILS approach was 4.46
degrees (7.8%).
Meteorology
The crew had a flight dossier that forecast
rain on arrival, with a possibility of snow (11).
During the approach they received the
following parameters: «runway
in use 18, wind is calm, instrumental visibility
is 2 km, snow, mist, FEW 500 ft,
BKN 1300 ft, 1800 ft OVC, temperature +0 ° C / -1 ° C, QNH 997, QFE 969, transition
level 70, runway is wet. « They thus expected
a landing on a wet runway.
An aerodrome warning message (12) issued at
the end of the afternoon reported snowfall:
« LFLB AD WRNG VALID 231700/242300
(HVY) SN (5 cm). Snowfall gradually is
reducing during the day, it will affect
the airport in the late afternoon and will
continue during the night and tomorrow in
the form of snow showers. Although low, the
expected snow depth may hinder aerodrome
activity. »The controller seeing that the grass
area around the runway was beginning to
whiten, the runway remaining black, asked,
twenty minutes before the Learjet’s landing,
for a grip measurement to be made. After the
measurement, it continued to snow.
Aeroplane performance
The performance calculation was made at the
time of flight preparation with software and
did not indicate any limitations. Conditions
being consistent with those were anticipated
during the preparation, the crew did not make
any in-flight calculations. The calculation
made using the flight manual graphs gives,
at a landing weight of 13,900 lbs, a landing
distance of 850 m on a dry runway. This
corresponded to a runway length required
of 1,420 m on a dry runway and 1,630 m on
a wet runway. On a runway contaminated
by ice, under the conditions on the day, the
maximum landing weight was 10,000 lbs. It is
notable, however, that the AFM only provides
performance figures for a «dry» or «frozen»
runway, without any means of calculation for
intermediate conditions.
Braking conditions on a runway.
There are several devices for measuring
braking coefficient on a snowy runway. The
most important aerodromes or those most at
risk are provided with equipment to measure
the coefficient on almost all of the runway.
Equipment that is lighter, for making spot
measurements, of the accelerometer type,
are available at most other aerodromes.
Finally, there is a « subjective » method for
assessing the quality of grip by means of
suddenly braking vehicle. This practice is not
recommended by the authorities.
The AIP France, in the « snow plan » section,
provides the following information:
Tapley type decelerometers are currently
available to perform measurements relating
to braking conditions: these devices
are mounted on commercial vehicles
with a weight of the order 1 000 kg. The
measurements are performed using Tapley
decelerometers only in the « Test » position
and making braking tests at a speed of 40
km / h, with sharp locking of the wheels
until the start of a slide. The braking tests
are carried out at distances ranging from
200 m and 400 m along lateral lines located
about 10 m on either side of of the runway
centre line and other locations considered
more representative of the condition of
a section of a determined runway. The
measurement result is expressed as a
coefficient... »
Measuring Equipment
The equipment used to Chambery was an
electronic decelerometer, manufactured
in Canada, whose operating principle was
identical to the above description. It was in
use at many French aerodromes. It had to
be installed on a vehicle not equipped with
ABS brakes or hydraulic shock absorbers (13).
After having compensated the device on the
vehicle, the driver had to drive at a speed
less than 40 km / h and stop suddenly to
block the wheels. The equipment records the
actual deceleration value which is converted
automatically to a friction coefficient. This
coefficient is called CRFI (Canadian Runway
Friction Index) which is different from friction
the ICAO friction coefficient. Its meaning is
given below.
The correspondence between the value
of the friction coefficient and the quality of
braking is not provided in the equipment
operating instructions, that users refer to.
The firefighters deploy this equipment (14)
at Chambery. Measurements are recorded
or printed out and sent to ATC services.
Braking conditions are transmitted to the
crews as « good » if the coefficient is greater
than 0.40 or directly using the value of the
coefficient. On the day of the event, the
friction coefficient measurement was made at
five points along the runway. At the displaced
runway 18 threshold, one at the markings,
another at the level of the central taxiway, a
fourth at displaced threshold 36 and a last
one a little before the central taxiway coming
back from the threshold of 36.
231524 LFLB 231400Z
36012KT 6000 RA BKN017
PROB30 TEMPO 1824 4000
SN SCT003 BKN010 =
(11)
(12)
The MAA are for
airport operators and
ATC organisations in
order that they can take
necessary steps when
specific phenomena are
expected.
(13)
These indications are not
mentioned in the equipment
user’s manual
The equipment had
only been received by
the users two months
previously. They had
then performed some
tests. This was only the
second runway friction
test performed. Use
of the decelerometer
was undertaken using
the instruction sheet
provided.
(14)
n° 7 - October 2007
7
Correspondance entre les coefficients CRFI et
OACI
1. 0
Bon
CRFI
μ
piste
1. 0
0. 53
0. 37
0. 8
OACI
μ
Moyen
piste
Bon
0. 6
0. 4
Moyen
Médiocre
0. 2
0. 17
Nul
8
0. 0
Médiocre
Douteux
The measurements were made as follows:
at a speed of 60 km / h, the driver braked
suddenly, without going as far as locking
the wheels although he noted the presence
of slush on the runway. Three values were
communicated to the controller: 0.44 at
threshold 18, 0.51 at mid-point and 0.55
at threshold 36. The result being superior
to 0.40, the braking was passed as «good»
on the ICAO scale available to the tower,
though it should be classified as «average»
according to the CRFI scale.
Lessons learned
As in the previous event, getting sufficient
braking information with the measuring
device did not result in reporting the
presence of melted snow on the runway.
In addition, the measurement was made
without blocking the wheels, so its reliability
was also compromised. Agents carrying
out these measures do not always receive
adequate training to ensure the best use of
measuring devices and ensure the validity
of the information transmitted. Finally, it
is noticeable that the crew, even if they
had received correct information about
the braking coefficient, did not have data
onboard for evaluating landing performance
under these conditions.
Not all of those involved, whether aircrew or on the ground, are always aware of the various
risks associated with operations in winter conditions. By understanding these phenomena
and their consequences, everyone can act effectively in these conditions, which, although
rare, can be very hazardous.
Online publications, some of which were used for the publication of this issue, provide
details on these matters. These include:
On aerodrome Snow Plans:
Publication of the DGAC destination aerodrome operators
http://www.stac.aviation-civile.gouv.fr/publications/documents/deneigement.pdf
Report on incident to two Orly MD 83 registered F-GHEI and F- GFZB on 2 December 1997
http://www.bea.aero/docspa/1997/f-ei971202/pdf/f-ei971202.pdf
On friction coefficients:
Boeing presentation at the Flight Safety Foundation seminar in Paris in 2006, entitled
«Airplane Deceleration on Slippery Runways: What You Should Know by Mark H. Smith,
Boeing Commercial Airplanes’
http://www.flightsafety.org/pdf/iass06_toc.pdf (not downloadable)
On de-icing operations:
Incidents in Air Transport No. 1 on icing
http://www.bea.aero/francais/rapports/rap.htm
On winter conditions:
NASA site
http://aircrafticing.grc.nasa.gov/courses.html
Incidents in Air Transport
Ministère de l’écologie, du Développement et de l’Aménagement durables
Bureau d’Enquêtes et d’Analyses (BEA) pour la sécurité de l’aviation civile
Directeur de la publication : Paul-Louis Arslanian
Responsable de la rédaction : Pierre Jouniaux - incidents@bea-fr.org
Conception-réalisation : division information et communication
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