Seconds after takeoff, AI 171's fuel control switches cut off: AAIB in initial report on plane crash

New Delhi | The engine fuel control switches of the Air India's ill-fated Boeing 787-8 plane were cut off seconds after of lift off, with one of the pilots asking the other why did he cut off and the latter responding saying he did not do so, according to AAIB.

In its 15-page preliminary report on the crash which happened in around 30 seconds of the plane lifting off, the Aircraft Accident Investigation Bureau (AAIB) on Saturday said the fuel control switches were switched on later but the deceleration in one of the engines could not be stopped.

On June 12, Air India's Boeing 787-8 aircraft operating flight AI 171 en-route to London Gatwick crashed into a medical hostel complex soon after take-off from Ahmedabad, killing 260 people, including 241 persons who were onboard the plane.

Releasing the report a month after the fatal crash, the AAIB said the aircraft air/ground sensors transitioned to air mode, consistent with liftoff at 08:08:39 UTC (13:38:09 IST).

"The aircraft achieved the maximum recorded airspeed of 180 Knots IAS at about 08:08:42 UTC and immediately thereafter, the Engine 1 and Engine 2 fuel cutoff switches transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec," the report said citing the plane's Enhanced Airborne Flight Recorders (EAFR).

As per the report, the engine N1 and N2 began to decrease from their take-off values as the fuel supply to the engines was cut off.

"In the cockpit voice recording, one of the pilots is heard asking the other why did he cutoff. The other pilot responded that he did not do so," it said.

AAIB said the CCTV footage obtained from the airport showed Ram Air Turbine (RAT) getting deployed during the initial climb immediately after lift off.

"No significant bird activity is observed in the vicinity of the flight path. The aircraft started to lose altitude before crossing the airport perimeter wall," it said.

As per the EAFR, the engine 1 fuel cutoff switch transitioned from CUTOFF to RUN at about 08:08:52 UTC. Thereafter at 08:08:56 UTC, the engine 2 fuel cutoff switch also transitions from CUTOFF to RUN.

"When fuel control switches are moved from CUTOFF to RUN while the aircraft is inflight, each engines full authority dual engine control (FADEC) automatically manages a relight and thrust recovery sequence of ignition and fuel introduction," the report said.

"The EGT (Exhaust Gas Temperature) was observed to be rising for both engines indicating relight. engine 1's core deceleration stopped, reversed and started to progress to recovery. Engine 2 was able to relight but could not arrest core speed deceleration and re-introduced fuel repeatedly to increase core speed acceleration and recovery," the report said.

The EAFR recording stopped at 08:09:11 UTC (Coordinated Universal Time).

At about 08:09:05 UTC, one of the pilots transmitted 'MAYDAY MAYDAY MAYDAY' and when the Air Traffic Controller (ATCO) enquired about the call sign, there was no response but the ATCO observed the aircraft crashing outside the airport boundary and activated the emergency response.

"At 08:14:44 UTC, Crash Fire Tender left the airport premises for Rescue and firefighting. They were joined by Fire and Rescue services of local administration," the AAIB said.

On December 17, 2018, the Federal Aviation Administration (FAA) had issued a Special Airworthiness Information Bulletin (SAIB) regarding the potential disengagement of the fuel control switch locking feature.

The SAIB was issued based on reports from operators of 737 airplanes that the fuel control switches were installed with the locking feature disengaged.

AAIB noted that the concern was not considered an unsafe condition that would warrant airworthiness directive by the FAA.

"The fuel control switch design, including the locking feature, is similar on various Boeing airplane models including part number 4TL837-3D which is fitted in B787-8 aircraft VT-ANB.

"As per the information from Air India, the suggested inspections were not carried out as the SAIB was advisory and not mandatory," the report said.

According to AAIB, the scrutiny of maintenance records revealed that the throttle control module was replaced on VT-ANB in 2019 and 2023.

"However, the reason for the replacement was not linked to the fuel control switch. There has been no defect reported pertaining to the fuel control switch since 2023 on VT-ANB," it said.