Air France A320 at Marseille on Mar 11th 2013, approach to stall during visual approach
Last Update: July 7, 2015 / 15:31:36 GMT/Zulu time
The French BEA reported in their weekly bulletin that the occurrence was rated a serious incident and an investigation by the BEA has been opened.
On Jul 7th 2015 the French BEA released their final report in French concluding the probable cause of the incident was:
During the turn onto final the aircraft was operating with a low energy reserve given its altitude and configuration, a nose up in order to turn led to a "SPEED, SPEED, SPEED" warning and subsequent activation of Alpha Floor Protection.
The following factors contributed to the incident:
- an inprecise instruction by the air traffic controller was interpreted by the crew as an invitation to conduct a short circuit, not catered for in the operating manuals
- the distribution of roles caused the pilot flying not having the runway in sight
- the failure to identify the risks associated with the FULL configuration at the end of the downwind leg and thus the reduction of stall margins during base and final turn
- reduced vigilance probably due to the routine established in repeated operation into the aerodrome, where the flight crew was based
- the absence of calls by the pilot monitoring who throughout the approach remained confident in the capabilities of the pilot flying to continue the operation
- a procedure that is not a memory item in the quick reference handbook but requires immediate reaction by the pilot flying
The investigation was unable to determine whether a reset of the flight management and guidance system at the time when the pilot flying was reducing speed and that remained undetected for 30 seconds, contributed to the incident.
The BEA reported the first officer (no data provided) was pilot flying, the captain was pilot monitoring. Marseille's runway 31R was closed due to work in progress. While on approach to Marseille's runway 31L the crew did not indicate preference for left and right hand circuit, the controller offered a left hand circuit for a rather short circuit, which was accepted by the crew, flaps 1 were deployed followed by flaps 2. The autopilot and flight director were disengaged, the autothrust remained engaged in speed mode. The aircraft joined downwind at 3450 feet MSL at 190 KIAS. The landing gear was lowered, the aircraft slowed to 160 KIAS and flaps 3 were selected, the aircraft was descending through 2500 feet at 900 feet per minute rate of descent at that point. The crew selected managed speed, which selected a speed of 145 KIAS for configuration 3. While slowing through 156 KIAS the FMGS encountered an internal fault and performed a hard reboot resulting the managed speed selection changed to selected speed setting maintaining current speed resulting the engines accelerating to maintain current speed. The aircraft descends between 1000 and 1600 fpm, 33 seconds after the FMGS reset the crew selects managed speed again which activates Vapp set at 136 KIAS. The engines slow to 30% N1. The aircraft joins the base leg, on the base leg descending through 1250 feet MSL at 900 fpm rate of descent, the pilot flying initiates the turn to final about 2.4nm from the runway threshold, the vertical speed increases briefly to 1900 fpm, the first officer applies a nose up control input lasting for 6 seconds at about 900 feet MSL, which reduces the rate of descent to about 500 fpm at a pitch angle of 6 degrees nose up, as result the speed quickly decays from 143 to 132 KIAS, bank angle 26 degrees to the left. About 1.9nm before the runway threshold, at 775 feet MSL/650 feet AGL the pitch angle reached 12 degrees nose up and the alpha floor protection activated resulting in TOGA LOCK, the engines accelerated, the pilot monitoring called out "Alpha Floor", 7 seconds later, as the aircraft accelerated through 142 KIAS, the thrust levers are moved into the IDLE detent and back into the TOGA detent disengaging the TOGA LOCK mode, the pilot flying adjusts the pitch for a go around and the aircraft, after reaching a minimum of 474 feet AGL, began to climb. The aircraft subsequently positioned for another approach and landed safely.
The BEA reported that the reboot of the FMGS was caused by an internal failure in the lateral guidance which could not identify the position of the aircraft for more than 5 seconds. The reboot caused the managed speed mode to revert to selected speed mode, an error which was corrected in a firmware revision S6 proposed to operated in June 2011, at the time of the occurrence about 48% of the aircraft affected had been upgraded. F-HBNE was still standard revision S4.
The BEA reported that due to terrain constraints approaches to runways 31 require a slope of 4 degrees (also PAPI indication). The majority of flights prefer a right hand visual circuit onto the runways, however, the possibility for a left hand circuit does exist. The possibility of a short left hand circuit, with the final turn over the motorway (about 3nm before threshold), was frequently used when Air France operated Boeing 737s, but is now rarely used.
The pilot flying provided testimony that because of relatively short final he decided to configure FULL configuration at the end of the downwind. The BEA annotated that standard procedure advocated by Air france is to use configuration 3 until being established on final, then apply FULL configuration.
On hearing the "SPEED SPEED SPEED" automated call the pilot flying was surprised by the lack of response from the autothrust system and hesitated for a few seconds without adjusting thrust levers. The speed therefore dropped further resulting in the activation of the Alpha Floor Protection. The QRH requires upon "SPEED SPEED SPEED" to increase the thrust settings until the alarm stops and trim if necessary. This procedure is not a memory item and is rarely seen during pilot training.
This article is published under license from Avherald.com. © of text by Avherald.com.
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