On 22 July 2011 an Airbus A340-300 being operated by Air France on a scheduled passenger flight from Caracas to Paris CDG at FL350 in night Instrument Meteorological Conditions (IMC) encountered moderate turbulence which led to an overspeed annunciation which was followed by the aircraft abruptly pitching up and a gain of over 3000 feet in less than a minute before it was returned to the previous cruise level. There were no injuries to any of the 284 occcupants. It appears that the relief First Officer was not present in the flight deck during the event.
An Investigation was carried out by the French Bureau d'Enquêtes et d'Analyses (BEA). Flight Data Recorder (FDR) data was available but Cockpit Voice Recorder (CVR) data had been overwritten preventing any evaluation of the Crew Resource Management aspects of the event including the “lack of monitoring of the basic parameters and the flight path” which the Investigation eventually found had played a major part in the event. Both operating crew were experienced on type.
It was established that the aircraft commander had been PF and that the cruise speed prior to the event had been M0.83. FDR data showed that the turbulence encounter began suddenly and lasted approximately one minute. During this time, the indicated airspeed increased quickly to M0.87, just above the Aircraft Flight Manual (AFM) MMO of M0.866 triggering the ‘OVERSPEED’ warning. The First Officer had responded by pressing the side stick takeover button, which disconnected the AP, and making a significant pitch up input without the awareness of the PF in respect of either action. The aircraft climbed rapidly with a pitch attitude of up to 12º at up to 5700fpm to a maximum of just over FL380, by which time speed had reduced to M0.66. The PF was unaware of what was happening and stated to the Investigation that he “noted with surprise that altitude was 38,000 feet and asked the PNF if they were cleared for FL350”. Only as the aircraft was descending through 36,520 feet some 30 seconds after the maximum altitude had occurred did the PF realise that the AP was not engaged. Once the cleared level had been regained, the AP and A/T were reengaged and the flight completed to destination without further event.
The vertical profile of the excursion flown. Reproduced from the Official Report.
The Investigation considered the use of the onboard weather radar and noted that there was no direct advice on tilt settings in either Air France FCOM or the Airbus FCTM but noted that such appears in an Airbus-authored generic Briefing Note on this subject Airbus FOBN:Adverse Weather Operations - Optimum Use of the Weather Radar. It was found that “the adjustment of the weather radar (had not been) the most suitable for detecting the convective zone crossed.
The activation of angle of attack protection (“Alpha Prot”) for over half of the 2 minute excursion was noted, as was the fact that this protection had been activated only because Normal Law had remained until the aircraft commander had pitched down for at least a second when the angle of attack was less than the maximum this protection mode permits - ‘Alpha MAX’. The inverse relationship between the Alpha Prot threshold applies and the prevailing Mach Number was also noted.
It was determined that:
- If the AP had not been manually disengaged, it would have remained engaged; there would not have been a significant trajectory deviation, with a gain in altitude of about 200 feet.
- Without the high angle of attack protection, the aeroplane would have kept its ascending trajectory until the triggering of the stall warning”.
- The AP disconnect warning had been rendered inaudible to both pilots by the concurrent sounding of higher category alerts, a situation which although in accordance with the 1995 type certification of the A340 would no longer meet current certification requirements.
The ‘startle effect’ of unexpected occurrences and the effect this can have on some pilots was considered. It was considered that “The PNF, probably surprised by the “OVERSPEED” warning as well as by the unanticipated turbulence, experienced a “startle” effect.”
In that context, it was observed that:
“Sometimes (such a sudden) effect sparks primal instinctive reaction, instant and inadequate motor responses. These basic reflexes may prove to be incorrect and difficult to correct under time pressure and may affect the pilot’s decision-making ability. The surprise effect typically occurs when there is a difference between the mental representation that the pilot has of the aeroplane’s behaviour and its real behaviour (instrument failures, trajectory upset) or when an unexpected event occurs. Its intensity depends on the severity, frequency and predictability of the event, as well as the previous experience of the crew. In some cases the surprise effect may lead to:
- Disturbance of memorisation mechanisms
- Reduction or loss of situational awareness
- Forgetting procedures
- Absence of reaction or an over-long reaction time”
The formal Conclusions of the Investigation were that:
“This serious incident was due to inadequate monitoring of the flight parameters, which led to the failure to notice AP disengagement and the level bust, following a reflex action on the controls”.
Four Contributory Factors were also identified:
- The AP disengagement aural warning was not broadcast, because of (the simultaneous) “OVERSPEED” warning with higher priority.
- The turbulence encountered at the start of climb made parameter reading difficult.
- Checking AP engagement, as required in the operator’s “Severe Turbulence” procedure, was not carried out.
- Inappropriate use of the weather radar meant it was not possible to avoid entering a zone of turbulence.
Five Safety Recommendations were made as a result of the Investigation:
- that EASA introduce the surprise effect in training scenarios in order to train pilots to react to these phenomena and work under stress.
- that EASA evaluate the possibility of requiring that the autopilot disengagement aural warning for all aeroplanes of a maximum mass on take-off of more than 5.7 t be triggered in compliance with paragraphs AMC 25.1322 and AMC 25.1329(j) of the CS-25.
[Recommendation FRAN- 2012-022]
- that the DGAC ensure that operators provide training and practice to their crews enabling them to improve their use of weather radar.
- that the DGAC request that operators check, for example in the context of flight analysis or LOSA, that the use of weather radar is in accordance with procedures or best practices.
- that EASA and ICAO require that the minimum recording duration of CVR’s be increased to allow the recording in full of long-haul flights.
The Final Report of the Investigation was published in May 2012 with an English language translation being made available on 12 June 2012.