Indian investigators have disclosed that the crew of a GoAir Airbus A320 shut down the wrong engine after experiencing powerplant vibrations following a birdstrike on take-off.
The aircraft (VT-GOS) had been departing runway 09 at Delhi, bound for Mumbai, on 21 June 2017.
At around 115kt the aircraft suffered a birdstrike on the right-hand CFM International CFM56 powerplant.
While an automated advisory alerted to high vibrations on the right-hand engine, this was not called out by the first officer, says the Indian government’s inquiry into the event.
Although the first officer queried whether the captain wanted to reject the take-off – as the jet was still far below the V1 decision speed of 146kt – the captain opted to proceed and diagnose the situation once airborne.
The inquiry says the captain had received “no input” regarding the engine vibration.
Once airborne the first officer “misinterpreted” the N1 speed reading of the right-hand engine as a vibration of the left-hand engine, the inquiry states.
The first officer called out a beyond-limit vibration of the unaffected left-hand engine and, as a result of the incorrect assessment, the left-hand engine was incorrectly shut down around 30s after rotation.
Thrust of the problematic right-hand engine was increased and the aircraft was left to climb on this engine alone for over 3min.
The first officer, says the inquiry, “repeatedly” advised the captain, incorrectly, that the left-hand engine was experiencing out-of-limit vibration.
Air traffic control directed the aircraft to stop climbing at around 3,300ft and the captain subsequently realised that the vibration was actually affecting the right-hand engine.
The crew, recognising the error, began to restart the left-hand engine but – before it was fully operational – reduced the thrust on the right-hand engine to ‘idle’.
Investigators point out that, at this stage, the aircraft was flying only on idle thrust from an engine which had been suffering technical problems. The initial attempt to restart the left-hand engine resulted in a fault, and the crew increased power on the right-hand engine while rectifying the situation.
Once the first officer confirmed the left-hand engine was available, the thrust on the right-hand engine was again reduced to ‘idle’ and that on the left-hand engine set to ‘climb’.
In the process of starting the engine, says the inquiry, the aircraft “lost a considerable amount of energy” but the crew “did not notice” that the airspeed was bleeding away, to as little as 127kt.
Combined with the crew’s manual handling, because the autopilot kept disengaging, this resulted in the activation of the A320’s stall-protection system. This activation persisted for 28s until the aircraft had descended to 2,600ft.
The crew continued to receive vibration alerts for the right-hand engine, which remained in an out-of-limit state for 6min.
Investigators add that the crew returned to Delhi to land, but initially had to execute a go-around because the aircraft was too high on the approach. The aircraft landed on runway 10 without further incident, on a single engine, on its second attempt.
The inquiry says the captain did not refer to the quick-reference handbook for the vibration situation after departure, and shut down the wrong engine instead of simply reducing the affected engine’s thrust below an advisory threshold.
It adds that the captain “never checked and confirmed” the first officer’s observations, even though the first officer was misidentifying the affected engine.
Even after realising the error the crew failed to follow the correct procedure to restart the left-hand engine, resulting in the fault which delayed the relight.