Jetstar A320 at Sydney on Feb 6th 2012, thrust lever asymmetry during takeoff and early rotation
Last Update: January 22, 2013 / 17:44:17 GMT/Zulu time
The Australian Transportation Safety Board released their final report concluding the probable cause of the incident was:
Contributing safety factors
- After the thrust levers were placed in the MCT/FLX detent, the right lever was inadvertently moved forward of the detent, which caused the autothrust system to revert to manual thrust mode.
- The training captain recognised the thrust lever asymmetry situation, however the pilot flying did not, and this resulted in a miscommunication that was not resolved effectively between the crew.
Other safety factor
- The pilot flying misunderstood a command from the training captain and rotated the aircraft at a speed that was approximately 20 kts below the required rotation speed, which had the potential to result in a tailstrike.
The ATSB reported the left hand seat was occupied by a captain under training (ATPL, 14,317 hours total, 120 hours on type) transferring from a Boeing 767 to the Airbus A320, the captain assuming the role of pilot flying for the sector (in the following called captain). The right hand seat was occupied by a training captain (ATPL, 9,343 hours, 4,957 hours on type) assuming the duties of the pilot monitoring and commander of the aircraft (in the following called commander).
The ATSB reported that the Boeing 767 had a "thrust hold" mode which was thought equivalent to the manual thrust mode. Seeing the flex/manual thrust Flight Mode Announciator (FMA) indication the captain thus did not perceive anything abnormal.
The FMA indicated a thrust lever asymmetry with one lever in a detent and the other out of the detent by a "LVR ASYM" FMA indication, this indication however is inhibited below 100 feet AGL.
In a post flight interview the captain stated that he did not understand why the commander had called "thrust not set" as the man thrust indication did make sense to him in the phase of the flight and acceleration. He explained that the indication made sense to him as he viewed it similiar to the thrust hold mode on the 767.
The ATSB wrote: "The PNF (commander), while using standard phraseology, did not effectively communicate his understanding of the thrust lever asymmetry situation to the PF (captain). In part this was due to the training environment that they were operating in, and that this situation was an opportunity for the training captain to assess the PFÂ’s actions in a non-normal event." The ATSB further expanded: "The lack of FMA annunciation for the thrust lever asymmetry in this event, due to the aircraft being below 100 ft, meant the PF did not easily recognise this scenario during the takeoff. He was aware that the lever asymmetry message would show in some conditions, but had not comprehended that there could be an asymmetry condition and no message would be displayed."
After the commander realised the captain did not react to the lever asymmetry he called "Go ... TOGA" in order to signal the takeoff should continue with the levers in the TOGA detent, which would also resolved the asymmetry, however the captain misheard this as "rotate".
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This article is published under license from Avherald.com. © of text by Avherald.com.
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