AI-171’s flight to tragedy: A minute-by-minute account of events that led to Ahmedabad plane crash

New Delhi: The preliminary report of the Aircraft Accident Investigation Bureau on the June 12 Ahmedabad air crash has said that the fuel supply to both the engines of the Air India's Boeing 787-8 'Dreamliner' stopped just 3 seconds after the lift-off as fuel cut-off switches transitioned from RUN to CUTOFF position, one after the other, within a gap of one second.

Here is a minute-by-minute account of the events that unfolded in the ill-fated flight based on the 15-page report released early on Saturday.

Minute-by-minute

11:17 AM: VT-ANB, which will fly to Gatwick, lands in Ahmedabad from Delhi; Lodges Pilot Defect Report 'STAB POS XDCR' (relates to Stabiliser Position Transducer, a sensor that communicates the horizontal stabiliser’s trim position to the aircraft’s flight control systems)

11:55 AM: Crew for Gatwick flight arrives at airport

12:10 PM: Troubleshooting carried out, aircraft released for flight

12:35 PM: Crew arrives at boarding gate

1:13 PM: Pilots request pushback and start-up; ATC approves pushback

1:18 PM: Aircraft departs bay

1:17 PM: ATC approved start-up

1:19 PM: To ATC query, pilots conform requirement of full length of Runway-23

1:25 PM: ATC grants taxi clearance on pilots’ request

1:32 PM: Aircraft transferred from Ground to Tower Control

1:33 PM: Aircraft instructed to line up on the Runway 23

1:37 PM: Aircraft cleared for Take-Off from Runway 23, Wind 240°/06 Kts

1:38 PM: Aircraft achieves maximum recorded airspeed of 180 Knots; Fuel cutoff switches of Engine 1 and Engine 2 transitioned from Run to Cutoff one after another with a time gap of one second

1:39 PM: 'Mayday' call from one of the Pilots; ATC enquires about call sign but no response; ATC observes aircraft crashing outside airport boundary, activates emergency response

1:44 PM: Crash fire tender leaves airport premises

Aircraft

• Year of Manufacture: 2013

• Total Aircraft Hours: 41,868

• Applicable airworthiness directives and alert service bulletins complied

On Board

• 54,200 kg fuel on board

• 2,13,401 kg take-off weight (Maximum allowed: 2,18,183 kg)

• No 'Dangerous Goods' on aircraft

From Cockpit Voice Recording

One of the pilots asks the other why he cut off (fuel cutoff switch). The other pilot says he did not do so

From CCTV footage

Ram Air Turbine (RAT) getting deployed during the initial climb immediately after lift-off. No significant bird activity observed in the vicinity of the flight path. Aircraft started to lose altitude before crossing the airport perimeter wall

Black Boxes

• Recovered on June 13 and 16

• Brought to Delhi on June 24

• Data downloaded after sourcing ‘Golden Chassis’ (Identical EAFR unit) and download cables from National Transportation Safety Board of the US

• 49 hours of flight data and 6 flights, including the event flight, recovered; Audio is two hours in length and captures the crash

• Initial analysis of the audio and flight data over

• Black box on the tail section of aircraft substantially damaged and could not be downloaded through conventional means; opened to inspect the memory card, damage is extensive

Fuel Control Switch

• FAA issued Special Airworthiness Information Bulletin (SAIB) in Dec 2018

• Regarding potential disengagement of the fuel control switch locking feature

• Airworthiness concern was not considered an unsafe condition that would warrant airworthiness directive by the FAA

• Air India says suggested inspections not carried out as the SAIB was advisory and not mandatory

• Scrutiny of maintenance records showed throttle control module was replaced in 2019 and 2023

• Reason for replacement not linked to the fuel control switch

• No defect reported pertaining to the fuel control switch since 2023

Investigation at this Juncture

• Wreckage site activities, including drone photography/videography completed; wreckage moved to a secure area

• Both engines retrieved and quarantined at a hangar in the airport

• Fuel samples taken from the bowsers and tanks used to refuel the aircraft tested; found satisfactory

• Very limited amount of fuel samples could be retrieved from the APU filter and Refuel/Jettison valve of left wing; Testing to be done at a suitable facility

• Cockpit data downloaded from the black box being analysed

• Statement of witnesses and the surviving passenger obtained

• Complete analysis of postmortem reports being undertaken to corroborate aeromedical findings with engineering appreciation

• Additional details being gathered based on the initial leads

• No recommended actions on Boeing or General Electricals, the manufacturer of engine

• Investigators to review and examine additional evidence, records and information