Pilots of the Airbus A320 involved in the gear-up touchdown at Karachi subsequently idled the only engine which was delivering power during the ill-fated attempt to execute a go-around.

The Pakistan International Airlines aircraft sustained damage to both CFM International CFM56 powerplants when their nacelles contacted runway 25L.

After the first officer urged the captain to take off again, the thrust levers were advanced to full thrust.

The left-hand engine’s power increased to 94% of N1, but that of the right-hand engine lagged at 16%, probably due to a transient loss of power to its electronic control unit during the runway contact.

As the aircraft climbed through 140ft the landing-gear lever – which had inadvertently been left up during the approach – was momentarily selected ‘down’ before immediately being returned to ‘up’.

Both engines reached 94% N1 at 442ft with the A320 travelling at 182kt and the crew cleaned the aircraft’s configuration.

PIA A320 crash-c-AAIB Pakistan

Source: AAIB Pakistan

Both CFM56 engines were damaged by runway contact during the gear-up touchdown

The thrust levers were briefly retarded to the maximum-continuous setting before being pushed back to full power.

“Both engines responded accordingly,” says the inquiry, although it states that oil quantities in each were falling. At 790ft the thrust levers were reduced to the climb detent and autothrust engaged.

The crew received oil-pressure warnings, initially for the left-hand, and then the right-hand engine, but cancelled the alarms.

At 1,270ft the autothrust switched to speed mode, with a target of 212kt compared with the aircraft’s speed of 243kt, and the thrust of both engines reduced.

Karachi approach control cleared the aircraft to climb to 3,000ft and turn left, to prepare for a second landing attempt.

As the aircraft entered the turn its left-hand engine speed began to decline, indicating that it was suffering an uncommanded in-flight shutdown, and its generator stopped supplying power.

But a few seconds later, the first officer remarked: “Thrust lever number two idle, move number two to idle.”

This thrust lever – which controls the right-hand engine – was reduced to the ‘idle’ setting immediately afterwards, while the lever for the left-hand engine was kept at climb power.

PIA A320 engine debris-c-AAIB Pakistan

Source: AAIB Pakistan

Debris of the right-hand engine, which was idled while still running after the left-hand engine failed

Speeds of both engines declined. At 3,140ft neither generator was producing electrical power, and the ram-air turbine automatically deployed. The flight-data recorder stopped operating and only the cockpit-voice recorder continued.

Analysis of the cockpit-voice information shows that the crew started receiving stall warnings and altitude alerts, prompting a query from Karachi approach control about the aircraft’s declining height.

The recording also reveals that – about 1min after the right-hand thrust lever was idled – the crew discussed the status of the right-hand engine, confirming that it was running.

Spectral analysis shows the engine’s speed subsequently started increasing. As the crew worked through procedures, the captain told the first officer: “You had selected engine number two to ‘idle’, whereas engine number one was gone.”

The inquiry says the right-hand powerplant, “the only running engine”, had remained idle for about 1min “until [the] flight crew eventually realised it” and advanced its thrust lever, adding that this showed a “lack of airmanship and situational awareness”.

Thrust available from the damaged engines after the runway strike could not be simulated or ascertained, states the inquiry.

“It is also not possible to estimate the additional power available if [the right-hand engine] was not retarded to idle,” it adds, preventing investigators from determining whether a safe landing during the go-around could have been achieved.

While the right-hand engine had been delivering power, its speed fluctuated before settling at about 65% of nominal for a short period. But spectral analysis indicates the speed then started to decrease until it was below the point of detection.

The inquiry says a sequence of stall warnings followed, and the first officer told Karachi controllers: “We have lost engines.”

It states that the A320 continued to descend. The landing-gear was extended below 800ft, but the aircraft crashed in a residential area of Karachi about 1,340m short of the runway. Only two of the 99 occupants survived the 22 May 2020 accident.