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Old 30th Jan 2014, 09:01
  #1257 (permalink)  
NigelOnDraft
 
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If you read the report thoroughly, you will find that it was indeed caused by differential power, due to a fault in the sensing system for the engine power which was not picked up during maintenance because the full test was not carried out. When the thrust levers were moved back past the gate, the fault produced a negative torque in one engine which caused the aircraft to bank sharply 40 degrees to the left. The PF then attempted to correct this by pushing the levers forward and then overcorrected to the right. You are correct in that the aircraft was far too low at the point and so the roll to the right caused the right wingtip to impact with the ground. However, the actual cause was the differential in power between the two engines.

Sunnyjohn, you must have read a different accident report. The differential power issue had been with that aircraft for some time, and certainly had been experienced and handled by the crew in the two preceding go-arounds. By all means it may have been a factor that contributed to the eventual cause, as was the wierd "combined" effort of flying the aircraft (PF on the yoke, and PNF on the power levers) and the mis-hadling that led to negative torque being commanded to the left engine, but the main cause of the crash was busting the approach minimums.
My reading of the report, albeit recollection, as is Sunnyjohn says.

The torque "difference" was not a significant factor in normal ops, and an indication based issue. The trouble was, with the (partial) beta selection, the reduction in torque PLUS the error led to a "negative" torque being "sensed", in turn leading that prop (only) to feather. This led to a much more significant asymmetric issue than the original issue, and led to the roll (as warned about by the manual). This led to an immediate left roll, almost certainly countered by the PF (P2) with right aileron. When the PNF (P1) applied full power, the asymmetry was removed, but the right aileron not = right roll as at impact.
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