An investigation into the Air India Boeing 787-8 crash showed that the fuel-controlled cutoff switch was activated as soon as the aircraft rose, but the status of the switch movement was not explained.
Preliminary findings from the Indian Aircraft Accident Investigation Bureau state that both “transition” to each other to a “cutoff” position, “transition” within a second, and simply stated, without indicating whether they accidentally or intentionally, by the crew, or if any other object or force interfered.
Investigators point to the aircraft reaching 180kt about three seconds after lift-off, and the switch transition occurs “quickly afterwards.” That is, the aircraft experienced a 3-4-second powered flight as it attempted to leave Ahmedabad's runway 23 on June 12th.
The fuel cut-off toggle switch progresses for takeoff and early climbing and is located behind the thrust lever prior to the engine fire extinguisher discharge handle.
Neither pilot will reach behind the thrust lever during regular takeoffs, immediately after lift-off. The crew usually confirms a positive climb, and about 10 seconds after turning, raise the landing lever onto the instrument panel ahead.
The 787 has a stabilizer cutout switch and an alternative pitch trim switch to the left of the fuel cutoff switch. The nose-up trim is directed by pushing the switch down. However, pitch trim is usually controlled by a switch on the pilot's control column.
Investigators noted that when the aircraft arrived in Ahmedabad, defects in the stabilizer's position transducer had been recorded. The investigation involved troubleshooting the failures and the aircraft was released for service to London Gatwick. It has not been shown whether this is related or not.
Preliminary findings say that aircraft deployed began to lose height even before they cleaned the airport's boundary walls.
Investigators have not confirmed how long the fuel switch is in the cutoff position by the time the crew notices. The investigation responded that without a direct transcription of the exchange, one pilot only called for why the other pilots had turned off, while the other pilots replied that he had not turned off.
However, after the switch moved to “cutoff”, the left engine returned to its “run” position for less than 10 seconds, then moved 4 seconds after the right engine. This started automatic regeneration, but was successful, but the process was unable to restore enough driving force to arrest the 787 descent.
Inspection of the wreckage shows the aircraft's flap handle at the usual 5° takeoff setting and the landing gear lever is still down. Although both thrust levers were approaching the idle position, flight recorder data shows that both continued to advance in the takeoff thrust setting until the impact. Both fuel control switches were in the “run” position.
The reason for the initial movement of the fuel switch has not been identified, but the investigation mentions a safety recommendation from the US FAA, which states that it may fit eight Boeing models, including three variations of the 787, but the locking system could be released based on reports from 737 operators.
“To move a switch from one position to another with the lock function involved, the pilot must lift the switch while moving the switch position,” says the December 2018 Special Airworthiness Breaking News.
“If the lock function is released, the switch can be moved between two positions without lifting it during the transition, exposing the switch to the possibility of careless action.”
It points out that such an error could cause the switch to move to the “cutoff” position, and there is a risk of engine shutdown during flight. Although not mandatory, we recommend ground inspection of the locking mechanism to “ensure engagement” by checking whether the switch can be moved between the two positions without lifting.
“If you can move without lifting the switch, the lock function will be released and the switch will need to be replaced at a faster opportunity,” the breaking news adds.
Both pilots were experienced with the 787. The captain had nearly 8,600 hours on the type, and the assistant officer on the flight had over 1,100 hours.
Investigators confirmed that out of the 242 residents, one passenger survived the accident.
