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- 20/09/2010, 01:49 #1
Informe: Accidente Air New Zealand 2008 en pruebas, costa francesa.The French BEA have released their final report in French and in English concluding the probable cause was:
Loss of control of the aeroplane by the crew following the improvised demonstration of the functioning of the angle of attack protections, while the blockage of the angle of attack sensors made it impossible for these protections to trigger.
The crew was not aware of the blockage of the angle of attack sensors. They did not take into account the speeds mentioned in the programme of checks available to them and consequently did not stop the demonstration before the stall.
- The decision to carry out the demonstration at a low height.
- The crew’s management, during the thrust increase, of the strong increase in the longitudinal pitch, the crew not having identified the pitch-up stop position of the horizontal stabiliser nor acted on the trim wheel to correct it, nor reduced engine thrust.
- The crew having to manage the conduct of the flight, follow the programme of in-flight checks, adapted during the flight, and the preparation of the following stage, which greatly increased the work load and led the crew to improvise according to the constraints encountered.
- The decision to use a flight programme developed for crews trained for test flights, which led the crew to undertake checks without knowing their aim.
- The absence of a regulatory framework in relation to non-revenue flights in the areas of air traffic management, of operations and of operational aspects.
- The absence of consistency in the rinsing task in the aeroplane cleaning procedure, and in particular the absence of protection of the AOA sensors, during rinsing with water of the aeroplane three days before the flight. This led to the blockage of the AOA sensors through freezing of the water that was able to penetrate inside the sensor bodies.
Probably contributing factors:
- Inadequate coordination between an atypical team composed of three airline pilots in the cockpit.
- The fatigue that may have reduced the crew’s awareness of the various items of information relating to the state of the systems.
The BEA listed following findings:
- The accident occurred in the context of the transfer of the aeroplane, from XL Airways Germany to Air New Zealand, at the end of a leasing contract.
- The leasing contract provided for a flight at the time of the handover of D-AXLA to XL Airways Germany and a flight at the time of its re-delivery to Air New Zealand, according to the Airbus flight check procedures.
- No flight check procedure is defined in the Airbus A320 Maintenance Manual or in the other documents available to operators.
- The regulatory texts relating to non-revenue flights do not mention the flights that can be performed at the time of the transfer of an aeroplane at the beginning or end of the lease.
- The XL Airways Germany operations manual does not mention the specific flights taking place in the context of the transfer of an aeroplane at the beginning or end of the lease.
- The programme of checks specified by the contractual leasing agreement was developed by Air New Zealand based on the manual used by Airbus for customer acceptance flights, which are performed by test crews.
- The crew had licences and qualifications to undertake the flight but did not have the technical skills, the experience, and the methods of a test crew to use this flight programme, even if it was not a test flight.
- The Airbus Customer Acceptance Manual specifies performing the low speed check in landing configuration at FL 140.
- The programme of checks developed for the leasing of D-AXLA did not reproduce in an identical manner the altitude range at which the low speed check should take place.
- The maintenance work was performed or checked in accordance with the approved maintenance programme and by part 66 qualified personnel.
- Painting and external finish operations are not included in the classes and categories of part 145 approvals.
- The stripping and cleaning procedures for the aeroplane, which include rinsing, specify protection of the angle of attack sensors.
- In order to eliminate the dust on the fuselage, a rinse with fresh water was performed on Monday 24 November 2008, without following the rinsing task procedure in the aeroplane cleaning procedure, and notably without any protection for the angle of attack sensors.
- During the rinsing, the angle of attack sensors were not protected. Water penetrated inside angle of attack sensors 1 and 2 and remained there until the accident flight, three days later.
- The AIP France specifies that flights of a specific nature must be subject to a specific request. Without an advance agreement, the flight can be subject to modifications in real time or possibly be refused if the circumstances require it.
- The Captain asked the Perpignan ATC service, on the morning of the accident, if the planned flight required specific airspace. The Perpignan controller indicated that it was not necessary as the crew of XL Airways Germany flight GXL032T had been able to follow a flight plan identical to that of the D-AXLA flight without any problems that morning.
- The crew consisted of two XL Airways Germany pilots. An Air New Zealand pilot, present in the cockpit, participated in an active manner in following the programme of checks.
- The CRNA southwest controller refused the request for manoeuvres by the Captain given that the flight plan that was filed did not include them.
- The crew adapted the programme of checks in an improvised manner, according to the constraints of the flight plan and the air traffic control service.
- Angle of attack sensors 1 and 2 blocked during cruise due to frozen water present inside the casing of these sensors. The system surveillance did not warn the crew of this blockage, which was more or less simultaneous and at identical local angle of attack values.
- The application of a jet of water onto an aeroplane without following the recommended procedure can allow penetration of a small quantity of water into the inside of an AOA sensor which is enough, when solidified, to block the sensor.
- The AOA sensors are not designed to be subjected to jets of fluids such as those encountered during de-icing, washing and cleaning operations.
- The CHECK GW message displayed on the MCDU, the consequence of the gap between the weights calculated by the FAC, on the one hand, based on the angle of attack, and on the other hand by the FMS, based on the takeoff weight and the consumption of fuel, was not detected by the crew.
- The crew decided, without preparation, and in particular without a call-out of the theoretical minimum speeds indicated in the OFC, to undertake the check of the low speed protections at an altitude of about 4,000 ft.
- The almost simultaneous blockage of the angle of attack sensors 1 and 2 at identical local angle of attack values rendered the angle of attack protections inoperative in normal law.
- The limit speeds corresponding to angle of attack protections displayed on the strip (Vaprot and Vamax) were underestimated and were directly proportional to the computed airspeed, due to the blockage of the angle of attack sensors.
- The crew waited for the triggering of these protections while allowing the speed to fall to that of a stall.
- The auto-trim system gradually moved the horizontal stabilizer to a full nose-up position during the deceleration. The horizontal stabilizer remained in this position until the end of the flight.
- The triggering of the first stall warning in normal law, at an angle of attack close to the theoretical angle of attack triggering the warning in landing configuration, indicates that angle of attack sensor 3 was working at that moment.
- When the stall warning triggered, the Captain reacted in accordance with the approach to stall technique.
- The flight control law passed to direct due to the loss of the normal law operating conditions. The auto-trim system was thus no longer available.
- The changes of law that followed did not allow the auto-trim system to move from the nose-up position.
- No crew member reacted to the USE MAN PITCH TRIM message.
- The Captain did not react with any input on the trim wheel at any time or to reduce engine thrust in any prolonged manner.
- Due to the position of the stabilizer at full pitch-up and the pitch-up moment generated by the engines at maximum thrust, the crew lost control of the aeroplane during the increase in thrust.
- The aeroplane was completely destroyed on impact with the surface of the sea.
The BEA analysed, that as part of the contract between XL Airways and Air New Zealand a "test flight" was to be conducted to verify the specified performance of the aircraft. The test flight was to be conducted in accordance with "Airbus check flight procedures". The Airbus Manuals do not contain such procedures. Air New Zealand therefore submitted a programme to XL Airways that was developed on the basis of demonstration flights Airbus conducts in the framework of new aircraft delivery to their customers.
There was confusion with the captain of the flight who initially referred to the flight as "flight test" or "check/acceptance flight" but later changed to "ferry/training flight". In this preparatory phase of the flight the performance did not come within a well defined framework, meaning the crew had to adapt and improvise in order to complete their task.
The flight was conducted XL Airways procedures, communication between the two XL Airways pilots occupying the left and right hand seat was conducted in German. Additional briefing necessary to keep the Air New Zealand pilot seated on the observer's seat updated was conducted in English, increasing the work load of the crew. At the same time, as the English communciation was between the captain and ANZ pilot, this tended to isolate the XL first officer who got him less involved in the performance of the checks.
At the end of the check flight the ANZ captain read the "low speed check in landing configuration" from the programme but did not mention altitude or speed to conduct the test at. The captain initially considered the IMC conditions while descending through FL80 made the test impossible and conducted the approach briefing, but interrupted the approach briefing about 2 minutes later. The low speed test was started as the aircraft descended through 4000 feet.
The resulting speed reduction was according to schedule at about 1 knot per second. The BEA analysed that the passive waiting for the trigger of the speed/stall protection suggested both the ANZ and XL captains began the test as a demonstration of stall protection rather than as a check of stall protection.
When the stall warning sounded, the XL captain placed the thrust levers into the TO/GA detent and pitched the aircraft down, however, that pitch down was insufficient for the automatic trim to vary the position of the horizontal stabilizer which had reached its nose up mechanical stop. The captain countered a left roll caused by the onset of stall, the resulting roll movements combined with the high angle of attack generated asymmetry which caused increasing speed differences measured by the Air Data Unit (ADR) 1 and ADR 2, which eventually caused the system to reject all three ADRs and caused the flight control to change to direct law. Under the combined effect of pitch up due to the engine acceleration, the pitch up due to increasing air speed and the horizontal stabilizer still at the mechanical nose up stop, even full side stick down input was insufficient to prevent the nose from pitching up. The XL pilots did not understand what was happening, the lack of reaction to the nose down inputs did not draw the attention of the crew to the stabilizer trim. The crew did not notice that the automatic stabilizer trim was no longer working. No attempt was made to adjust the trim manually or to reduce engine thrust.
This led to the airplane stall a second time this time irrecoverably.
The flight data recorders recorded almost identical but static values for the angle of attack sensors #1 and #2. This can not be likely explained unless both sensors became physically and almost simultaneously blocked. The sensors had no history of malfunction. The simultaneous blockage also rules out a mechanical failure. There was no evidence that the sensors were defective prior to impact in the water. The BEA further analysed that due to low humidity and the absence of failure of the sensor heating environment blockages can be ruled out, too, leaving only internal blockage possible.
Underneath the mounting plates of the angle of attack sensors there was still yellow paint suggesting, the angle of attach sensors had not been removed during re-painting of the aircraft. The area was masked making it impossible for the chemical stripper to penetrate inside the sensors.
The thickness of the paint on the fuselage rendered the chemical stripping insufficient and required the airplane to be sanded. Following the sanding the masking materials were removed from the airplane.
5 days later the aircraft was rinsed with fresh water to remove the dust collected from the sanding. The application of fresh water saved an amount of time in comparism to using clean dry cloth as recommended by painting procedures and shows the personnel doing the rinsing were not familiar with all the precautions necessary.
The angle of attack sensors were not protected during the rinsing and some water penetrated inside at least two of the three angle of attack sensors. The water remained inside the sensors for three days. The ambient temperatures encountered during the climb of the aircraft caused the water to freeze and block the sensors.
The seals of the angle of attack sensors showed no traces of damage prior to impact with water. Tests showed that specific washing conditions allowed a small amount of water to penetrate inside the sensor's upper bearing, which was enough to block the bearing and the sensor when frozen.
Noticia en el foro, 2008
- 20/09/2010, 03:06 #2
- 20/09/2010, 07:12 #3
- 05 sep, 08
- 20/09/2010, 08:33 #4
- 20/09/2010, 08:59 #5
La verdad es que hay veces que no entiendo como se cometen fallos así...
- 20/09/2010, 10:55 #6
Por esas fechas estaba yo en NZ, fue toda una tragedia nacional.
- 20/09/2010, 11:18 #7"God created AIRCRAFT MECHANICS so pilots can have heroes too"
“A wise man makes his own decisions; an ignorant man follows public opinion”
- 20/09/2010, 11:31 #8
Menuda cagada macho!!!
Alguien puede colgar por aquí un listado de los accidentes/incidentes de Air New Zealand?TRAFFIC!
Aérodromo de Requena
Club Aéreo Valencia
- 20/09/2010, 12:04 #9
- 20/09/2010, 12:19 #10
Creo que el informe final salió hace un año, aunque no lo puedo asegurar. Lo mismo era uno preliminar.
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