ITA n° 7
Contents
1. 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 In the Usage part of the Operations Manual there are other instructions concerning de icing 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 and disappears after takeoff Assistance providers Each provider is responsible for staff training An annual audit is performed by the quality assurance manager of the2. N 7 October 2007 0 This was the first aeroplane to land after the reopening of the runway 2 The landing weight was 10 0 1 Bureau d Enqu tes et d Analyses pour la s curit de l aviation civile Zone Sud Batiment 153 200 rue de Paris A roport du Bourget 93352 Le Bourget Cedex FRANCE T l 33 1 49 92 72 00 Fax 33 1 49 92 72 03 incidents bea aero Incidents in Air Transport Operations in Winter Conditions 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 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 the onboard document
3. 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 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 Saint Exupery was diversion aerodr
4. e aux freins Meilleures LL avion capacit s de freinage Conditions de freinage Piste glissante H piste point de glissance du pneu 1 avion capac Moins bonnes D c l ration disponible piste point de glissance du pneu it s de freinage Source Boeing F le Only the last ge pression iaou evaluation takes Piste seche Fractal i n t O accoun t certain aeroplane parameters However this information is not available the first plane landing Antickid I Antisk dy Freinage avion et coefficient de freinage R sum des m thodes Freinage avion calcul Freinage rapport Donn es du constructeur Coefficient den 4 LILET Re E 0 3 Pavion 39 The depth can be difficult to measure especially when water is present 4 WED Water Equivalent Depth 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 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 Source Boeing 2 Description Mesure du coefficient de la piste de freinage 1 0 OACI Meilleur freinage S
5. 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 1 99 7 f ei971202 pdt f ei9 71 202 padf On friction coefficients Boeing presentation at the Flight Safety Foundation seminar in Paris in 2006 entitl
6. che Coefficient 0 8 Mouill e de friction Neige s che 0 6 de la piste Neige mesur compacte Neige mouill e H Slush Glace Glace mouill e piste j 0 en Plus mauvais 0 0 freinage Coefficient Terme utilis Entre 0 39 et 0 36 Moyen Bon Medium Good Entre 0 29 et 0 26 Moyen Medium Poor m diocre 0 09 et en dessous 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 u which can not be directly compared to the runway u based on description of braking efficiency good average poor The difference between the runway u and plane u reflects the limits of the efficiency of the braking system Airbus bases its calculations on the type and depth of the contaminant 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 and provides limitations based on aeroplane landing CONTAMINATED RUNWAY MASSE MAXIMALE A L ATTERRISSAGE kg LONGUEUR DE PISTE DISPONIBLE m WED 4mm 6mm 8mm 10 mm 16 885 17 992 19 085 20 046 21 007 21 968 22 000 22 000 22 000 Specific Gravity rr z 0 125 Loose Dry Snow To obtain WED multiply
7. the day the maximum landing weight was 10 000 Ibs 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
8. airline that uses this service In the case under consideration the agents that might perform de icing anti icing 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 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
9. ation provided landing performance consistent with the weight of the aeroplane 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
10. 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 3 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 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 le
11. d colle 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 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 Incidents in Transport in Air Transport 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 th
12. e 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 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 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 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 I
13. e 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 Failure profile Broken part of actuator Communications on the meteorological situation Weather information at Lille Lesquin indicated between 14 h 40 and 15h 05 rain and sleet between 15 h 05 and 15 h 27 continuous rain between 15 h 27 and 16h 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 OOOft 5 temperature O 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 m7 October2007 7 October 2007 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 beginni
14. ed 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 7 on icing http www bea aero francais rapports rap htm On winter conditions NASA site http aircrafticing grc nasa gov courses html Minist re de l cologie du D veloppement et de l Am nagement durables Bureau d Enqu tes et d Analyses BEA pour la s curit de l aviation civile Directeur de la publication Paul Louis Arslanian Responsable de la r daction Pierre Jouniaux incidents bea fr org Conception r alisation division information et communication Incidents in Air Transport
15. 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 e a description of the runway surface type and depth of possible contaminant based on observations by aviation personnel on the ground e the friction coefficient of the runway runway u 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 e braking efficiency evaluated by the pilot at the time of landing and described as good fair or poor Freinage avion et coefficient de frottement D c l ration associ
16. g 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 ae
17. ng 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 OO 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 brok
18. ome Meteorological information was collected by the crew at Vienna then information received in flight made it possible to land at Chambery 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 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 Incidents in Ai Transport in Air Transport 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 During the approach they received the following pa
19. rameters 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 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 Ibs 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
20. roplane must be made to reduce the aeroplane s attitude 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 This was the only rainfall before aeroplane departure This was the first time that the agent had done this n 7 October 2007 This phenomenon cannot explain the sensation of effort on the elevator control during testing of this surface These operations are unusual a simplified guide may be useful to crews In the General section are 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 CCl others is responsible for The correct execution of the treatment and the result obtained Training support staff zal 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
21. rs 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 ona 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 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 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 Il 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 de icin
22. t 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 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 describing the state of the runway transmitting a SNOWTAM
23. theContaminant Depth by the Contaminant Specific Gravity o 0 2 Dry Snow 0 3 0 4 Wet Snow 05 0 85 Slush EA 1 0 walan Wet Slush Po 7 10 DEPTH OF CONTAMINANT mm 5 W E D mm 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 SLIPPERY RUNWAY LONGUEUR DE PISTE REQUISE m MASSE T OMPACTED f snow WET ICE WETICE 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 operato
24. vel 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 BKNO17 PROB30 TEMPO 1824 4000 SN SCT003 BKNO10 12 The MAA are for airport operators and AIC 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 14 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 7 Odtober2007 7 October 2007 Correspondance entre les coefficients CRFI et OACI 1 0 8 CRFI OACI 0 6 l H a 53 fu pisie 0 37 Moyen 0 17 star 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
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