Pakistani investigators believe consumption of alcohol prior to flight affected the judgement of a Shaheen Air Boeing 737's captain, prior to the jet's suffering loss of both main landing-gear after touchdown at Lahore.
The aircraft slid off runway 36L and came to rest nearly 200ft left of the centreline and just over 8,300ft from the threshold.
Pakistani investigation authority SIB states that the aircraft had conducted an unstable approach to the runway, with high speed having already followed an "incorrect" flightpath.
The aircraft had deviated from the correct track and the assigned altitude during the flight.
SIB says the crew's situational awareness had deteriorated and that the captain was suffering loss of concentration, "probably due to effects of alcohol".
The captain was found to have a blood-alcohol level of 83mg/dl. Impairment of the central nervous system, says the inquiry, begins at around 50mg/dl. No trace was found in the first officer.
As the aircraft touched down at Lahore, the probable presence of excess play in the shimmy-damper linkages in the left-hand main gear resulted in vibration and fracture as the wheels touched down, causing the gear to collapse.
Analysis suggested that a slow rate of contact for the left-hand gear "reduced the [effectiveness]" of the shimmy-damping mechanism.
The right-hand main gear – which, in contrast, had sustained a hard touchdown – then collapsed as a result of mechanical overload as the aircraft slid off the runway.
SIB says the aircraft had been serviced properly before the 3 November 2015 accident, and its maintenance history did not indicate any defect relating to left-hand main gear shimmy.
But it adds that the operator's maintenance schedule for shimmy-damper and linkage inspections was "not adequate", especially given that a Boeing service bulletin had outlined a need for enhanced checks.
Investigators put the airspeed at 166kt – and ground speed at 174kt – at the time of touchdown, higher than the reference speed of 134kt.
None of the 121 occupants was injured in the accident despite substantial damage to the aircraft.
Source: Cirium Dashboard