E-Paper
A glossary of the terms in AAIB’s report on the crash
The preliminary report on Air India Flight 171 reveals critical engine failures and fuel switch issues during takeoff, leading to a fatal crash.
The Aircraft Accident Investigation Bureau’s preliminary report into Air India Flight 171 is dense with aviation terminology that helps explain how investigators determined both engine fuel cutoff switches “transitioned from RUN to CUTOFF position one after another with a time gap of 01 sec.” Understanding these technical terms is crucial to grasping what happened during those fatal 32 seconds after takeoff.
The key technical terms that matter:
EAFR (Enhanced Airborne Flight Recorder): The report centres on data from the aircraft’s two EAFRs, which combine traditional “black box” functions into single units recording both flight data and cockpit voice communications. The forward EAFR provided the critical timeline showing exactly when fuel switches moved and engines began losing power.
Fuel Control Switches - RUN vs CUTOFF: These spring-loaded switches beneath the throttle handles control fuel flow to each engine. The report’s finding that both moved from “RUN” to “CUTOFF” within one second represents the accident’s central mystery—investigators still don’t know what caused this movement.
RAM Air Turbine (RAT): When both engines failed, this emergency windmill automatically deployed to provide backup electrical and hydraulic power.
V1, Vr, and V2 speeds: Critical take-off velocities that determine aircraft capabilities. V1 (153 knots) is the decision speed beyond which takeoff must continue; Vr (155 knots) is rotation speed for liftoff; V2 (162 knots) is the safe climbing speed. The engines failed just after reaching maximum speed of 180 knots, past all safety margins.
FADEC (Full Authority Digital Engine Control): This is a reference to the computer systems that automatically manage engine operations. When fuel switches returned to “RUN,” FADEC systems initiated automatic reignition sequences on both engines—but insufficient time and altitude prevented successful restart.
Mayday call: The international distress signal transmitted by the crew at 08:09:05 UTC. This standard emergency declaration came just 23 seconds after fuel cut-off and only six seconds before the recording ended, showing how rapidly the situation deteriorated.
UTC Timestamp: All times in the report use Coordinated Universal Time to provide precise chronology. The 29-second span from fuel cutoff (08:08:42) to recording end (08:09:11) represents the entire emergency sequence.
Initial climb phase: This is one of the most critical flight periods when aircraft are low, slow, and vulnerable. It was in this phase that the plane crashed.
Scan to read the full AAIB preliminary report.
[INSERT QR]
