sábado, 6 de agosto de 2011

Air France 447 - New Findings - Recommendations - Pilots' Talkings

AIRBUS 330 - Controles de Voo

Principio Básico

As superfícies de controle de voo do A330 são:
 - Eletricamente controladas
 - Hidraulicamente ativadas
O estabilizador e o leme/direção podem ser mecanicamente controlados.
Os sidesticks são usados para pilotar a aeronave com leme e direção.
Os comandos dos pilotos, são interpretados pelos computadores, os quais enviam sinais para mover os controles de voo necessários para realizar o curso de voo desejado.
Apesar do comando dos pilotos, os computadores previnem:
 - manobras excessivas
 - que os limites da segurança de voo sejam excedidos

In a schematic manner, the threshold is stable below a Mach of the order of 0.3, then reduces in a quasi-linear manner to a Mach of the order 0.75, after which it falls more rapidly when the Mach increases up to Mach 0.82.

Onboard weather radar

The Air France Airbus A330’s are fitted with Collins WXR 700X-623 type weather radar with a flat antenna (P/N : 622-5132-623). The opening angle of the radar beam is 3.6° in elevation and 3.7° in azimuth.
Adjustments to the tilt and the gain are made manually.
Each airplane is equipped with two systems, only one antenna and only one control box.
Only one system is active at a time.
The radar image is presented on the ND overlaid with navigation and TCAS information. It is presented when the radar is operating, when the ND is not in PLAN2 mode and when the TERR3 mode is not selected. Range adjustment is done manually
Note: Adjusting the luminosity of the terrain and weather information is done independently of that of other information on each ND.
No malfunctions of the weather radar were reported on the other ATL of F-GZCP in the last 6 months prior to the accident.
Instructions for use of weather radar

In cruise mode above 20,000 feet, a slight downwards adjustment of tilt, depending on the scale selected, is recommended so that the ground echoes only appear on the ND at the edge of the furthest distance circles. This method enables the simple and practical application of the height/tilt rule of equivalence providing the optimum tilt adjustment.
When pilots monitor the weather situation, gain can remain in CAL position. In the confirmed
presence of storms and during their avoidance, a manual adjustment can be used for comparison with the CAL image.
A scale of 160 NM enables the change in the weather situation to be assessed and anticipate route changes. A scale of 80 NM is used for avoidance. Short scales must be periodically discontinued in order to observe distant weather conditions and to avoid an impasse amid the disturbances.
The shape of the echoes may alert the crew to the possible presence of hail. Zones of turbulence may be presented above a detected zone of precipitation.
Red or magenta zones as well as fringe-shape echoes must in this way be by-passed from windward by regularly adjusting the tilt and the range. The avoidance decision must be taken before the echoes are at 40 NM.
The operator recommends avoiding flying less than 5,000 ft above or below a storm cell. It provides a formula for pilots to estimate the separation height between the top of a detected cell and the airplane. This formula uses the distance and the tilt points from which the zone echo disappears. Above 23,000 ft, it is recommended to fly more than 20 NM from these zones11.

Time (UTC)
Captain & PNF
1st Officer (PF)
Cleared to Start Up


Take Off  (TOW = 232.8) TakeOff Weight
Max. TOW = 233 Ton. Including Fuel = 70.4 Ton

Crew Informed ATLANTICO controller the aircraft passed INTOL Fix point and they estimated SALPU at 01:48 then ORARO at 02:00 UTC.

Controller asked them to maintain Flight Level 350 and the estimated time at TASIL Fix point.
01:35:53 to

Controller asked again three times for the estimated at TASIL Fix with no answer.
He woke the second copilot and said:
“…he’s going to take my place”
01:59:32 to
He attended the briefing between the two copilots
“the little bit of turbulence that you just saw we should find the same ahead we`re in the cloud layer unfortunately we can’t climb much for the moment because the temperature is falling more slowly than forecast”
“the logon with DAKAR failed”

The airplane approached the ORARO point maintaining Flight Level 350, MAC 0.82, Pitch Altitude 2.5°, Weight & Balance 205 Ton and 29%. Autopilot 2 and Auto-Thrust engaged.

Called cabin crew: “in two minutes we should enter an area where it’ll move about a bit more than at the moment, you should watch out”
He added: “I’ll call you back as soon as we’re out of it”
“you can maybe go a little to the left …”
The airplane changed the heading 12 degrees to the left. Turbulence level increased slightly and the speed was reduced to MACH 0.80.
The AUTOPILOT and   AUTO-THURST disengaged

Pilot Flying said: “I have the controls”

The airplane began to roll to the RIGHT and the Pilot Flying made a nose-up and LEFT input. The STALL WARNING sounded 2 times in a row.
The recorded parameters show a sharp FALL from about 275 Knots to 60 Knots in the speed displayed on the LEFT PFD, and then a few moments later in the speed displayed on the Integrated Standby Instrument System [ISIS].
There is no record on the Flight Data Recorder about speed displayed on the RIGHT side.

“we`ve lost the speeds then”
He added: “alternate law protections”

The airplane’s pitch attitude increased progressively beyond 10 degrees and the plane start climb.

PF made nose-down control inputs and alternately LEFT and  RIGHT  roll inputs.

The vertical speed reached 7000 feet/min, dropped to 700 feet/min and roll varied between 12° RIGHT and 10° LEFT. The speed displayed on the LEFT side increased sharply to 215 Knots (MACH 0.68). The airplane was at 37500 feet and the recorded AOA was around 4°.
PNF tried several times to call the Captain back

The STALL WARNING triggered again.
The TRUST levers were positioned in the TO/GA detent

The Pilot Flying maintained nose-up inputs

AOA [Angle Of Attack] was around 6° continued to increase.
The Trimmable Horizontal Stabilizer [THS] began a movement and passed from 3° to 13° pitch-up in about 1 minute and remained in the latter position until the end of flight.
50 seconds later
The speed displayed on the ISIS increased sharply towards 185 Knots.

The Pilot Flying continued to make nose-up inputs

The airplane’s altitude reached its maximum of about 38000 feet.  AOA and pitch attitude reached 16°.
The Captain re-entered the cockpit

During the following seconds all of the recorded speeds became invalid and the STALL WARNING stopped.

The altitude was then about 35000 feet, the AOA exceeded 40° and the Vertical Speed was about  minus 10000 feet/minute. The airplane’s pitch attitude did not exceed 15° and the engines’ N¹ were close to 100%. The airplane was subjected to roll oscillations that reached 40°.

The Pilot Flying made input on the Side-stick to the LEFT and nose-up stops, wich lasted about 30 seconds.

PF said: “I have no more displays”

PNF said: “we have no valid indications”

The Thrust levers were on IDLE detent, at that moment, and the engines’ N¹ were at 55%.
50 seconds later
PF made pitch inputs.

The AOA decreased, the speeds became VALID again and the STALL WARNING triggered again
PF said: “we’re going to arrive at level one hundred”

15 seconds later
Simultaneous inputs by both pilots on the side-sticks were recorded

PF said: “go ahead you have the controls”

AOA, while it was valid, always remained above 35°
The last recorded values were a Vertical Speed of minus 10912 feet/minute, a Gorund Speed of 170 Knots, Pitch Attitude of 16,2° nose-up, Roll Angle of 5.3° LEFT and a Magnetic Heading of 270°

No EMERGENCY message was issued by the crew

The wreckage was found at a depth of 3980 meters on 03 APR 2011 at about 6.5 Nautical Miles and to the North of the last position transmitted by the aircraft

The following tracks were recorded:

 track 1: radio communications and the signal from the microphones for the pilot seated on the left
 track 2: radio communications and the signal from the microphones for the pilot seated on the right
 track 3: radio communications, the signal from the second copilot’s microphone (rear seat), and the FSK signal
 a track made up from the first 3 tracks mixed together
 CAM track: the signal from the cabin area microphone

Analysis of the 5 audio files downloaded revealed that the event did not occur at the end of the sequence of data recorded on the 5 tracks, and that the tracks lasted for less than a few dozen seconds at the expected values.

Synchronisation of the various channels showed that some of the data was missing.
Moreover, analysis of the binary contents of the EEPROM memory confirmed the inconsistency of the pointers5 used by the manufacturer’s reader to start and end the downloading of the data.

Analysis of the flight recorder data

 Synchronisation of the recorders
The recorders were synchronised using the various alarms triggered during the flight, particularly the stall warning. The number of alarms made it possible to synchronise the recorders with an accuracy of approximately 100 ms.

The CVR recording started at about 0 h 09 UTC on 1 June.

 CVR analysis
The CVR audio recording starts at 00 h 09 min 15. The cockpit door was opened once at 0 h 26 min 19. It was later closed and opened again several times. It stayed opened for some time on several occasions. The door security system (electrical opening command by the pilots) was not heard on the overall recording.
At 0 h 36 min 26, an electrical phenomenon (audio discharge) linked to atmospheric conditions appeared on the CAM track and could be heard until the end of the recording. The following figure shows the distribution of those audio discharges as a function of time:


New Findings
 the composition of the crew was in accordance with the operator’s procedures,
 the airplane’s weight and balance were within operational limits,
 at the time of the autopilot disconnection, the Captain was taking a rest,
 the departure of the Captain was done without leaving any clear operational instructions, in particular on the role of each of the copilots,
 the crew had identified some echoes on the weather radar,
 the crew made a heading change of 12° to the left of its route,
 the AP disconnected while the airplane was flying at the upper limit of a slightly turbulent cloud layer,
 the copilots had not received any training, at high altitude, in the “Unreliable IAS” procedure and manual aircraft handling,
 there was an inconsistency between the speeds measured, likely following the blockage of the Pitot probes in an ice crystal environment,
 although having identified and called out the loss of the speed indications, neither of the two copilots called the procedure “Unreliable IAS”,
 the invalidity of the speed displayed on the left PFD lasted for 29 seconds, that of the speed on the ISIS for 54 seconds,
 in less than one minute after the autopilot disconnection, the airplane exited its flight envelope following inputs that were mainly pitch-up,
 the Captain came back into the cockpit about 1 min 30 after the autopilot disconnection,
 throughout the flight, the movements of the elevators and the THS were consistent with the pilot’s inputs,
 up to the exit from the flight envelope, the airplane’s longitudinal movements were consistent with the position of the flight control surfaces,
 there was no explicit task-sharing between the two copilots,
 there is no CRM training for a crew made up of two copilots in a situation with a relief Captain,
 no standard callouts were made on the disparities in pitch attitude and vertical speed,
 the airplane’s angle of attack is not directly displayed to the pilots,
 the approach to stall was characterised by the triggering of the warning then the appearance of buffet,
 neither of the pilots made any reference to the stall warning,
 neither of the pilots formally identified the stall situation,
 the stall warning was triggered continuously for 54 seconds,
 a short time after the triggering of the stall warning, the PF selected TO/GA thrust and made a nose-up input,
 the angle of attack is the parameter that allows the stall warning to triggered; if the angle of attack values become invalid, the warning stops,
 by design, when the measured speed values are lower than 60 kt, the 3 angle of attack values become invalid,
 each time that the stall warning triggered, the angle of attack exceeded the value of its theoretical trigger threshold,
 the engines functioned normally and always responded to the crew’s inputs,
 no announcement was made to the passengers.

Recommendations on Operations

Training for Manual Aircraft Handling

The investigation brought to light weaknesses in the two copilots: the inappropriate inputs by the PF on the flight controls at high altitude were not noted by the PNF through an absence of effective surveillance of the flight path. The stall warning and the buffeting were not identified either. This was probably due to a lack of specific training, although in accordance with regulatory requirements. Manual airplane handling cannot be improvised and requires precision and measured inputs on the flight controls. There are other possible situations leading to autopilot disconnection for which only specific and regular training can provide the skills necessary to ensure the safety of the flight. Examination of their last training records and check rides made it clear that the copilots had not been trained for manual airplane handling of approach to stall and stall recovery at high altitude.
Consequently, the BEA recommends:
 that EASA review the content of check and training programmes and make mandatory, in particular, the setting up of specific and regular exercises dedicated to manual aircraft handling of approach to stall and stall recovery, including at high altitude.

Relief Captain

The investigation showed that an absence of training and practice for a crew consisting of two copilots does not guarantee a level of performance equivalent to a crew consisting of a Captain and a copilot when faced with a degraded situation. The absence of a hierarchy and of effective task-sharing in the cockpit strongly contributed to the low level of synergy. The anxiety generated by the absence of the Captain from the cockpit shows that the two copilots were not capable of resolving this emergency situation. This can be explained both by the absence of any appropriate training and a lack of decision-making practice on the part of the two copilots. Numerous events turned out favourably due to the presence of the Captain whose training and experience made possible a more solid analysis and more serenereactions to the situation.
Recommendations relating to Certification

Angle of Attack Measurement

The crew never formally identified the stall situation. Information on angle of attack is not directly accessible to pilots. The angle of attack in cruise is close to the stall warning trigger angle of attack in a law other than normal law. Under these conditions, manual handling can bring the airplane to high angles of attack such as those encountered during the event. It is essential in order to ensure flight safety to reduce the angle of attack when a stall is imminent. Only a direct readout of the angle of attack could enable crews to rapidly identify the aerodynamic situation of the airplane and take the actions that may be required.

Consequently, the BEA recommends:
 that EASA and the FAA evaluate the relevance of requiring the presence of an angle of attack indicator directly accessible to pilots on board airplanes.

Recommendations relating to Flight Recorders

Analysis of the FDR parameters and audition of the CVR provide information that is essential to an understanding of the event. However, it is difficult to reconstruct the indications that were available to the crew on their instrument panel, especially the instructions given by the Flight Director crossbars when they reappear. It is also impossible to see whether there have been any attempts to re-engage the autopilot. A view of the instrument panel would complete the information provided by the FDR and the CVR and would make it possible to confirm the indications that were available to the crew and the actions that they made. Numerous recommendations have already been made on this subject over the past ten years without any real progress having been made.