British Airways has highlighted to crews the importance of avoiding distraction while conducting take-off calculations, after a low-thrust incident involving an Airbus A321’s departure from Glasgow.

The aircraft, bound for London Heathrow on 24 November last year, was being prepared for a full-length take-off from runway 05.

As part of the performance calculation the crew opted for low-thrust take-off, typically used to reduce noise and engine wear, by using a flex temperature of 49°C.

Entering a flex temperature that is higher than the actual outside temperature results in the engine control system adapting thrust to a lower – but still sufficient – setting for the supposedly hotter conditions.

But the UK Air Accidents Investigation Branch says the crew inadvertently entered a flex temperature of 79°C – unwittingly reducing the thrust level to be commanded during take-off.

The captain testified to the inquiry that he was unsure if he had said the wrong number when reading the flex temperature data or whether the first officer mistakenly pushed the wrong key.

Investigators state that, either way, the error was not detected – possibly because the crew was distracted by a cabin-crew call or the unusual acceleration altitude which was part of the departure calculation.

“The subsequent checks do not require the flight crew to refer back to the source data,” says the inquiry, adding that the selected flex temperature, while unusual for an A321, was not so for A319s which the crew had also flown.

Although air traffic control asked the crew, during taxi, whether they could depart from an intersection, the A321 (G-EUXJ) eventually began the take-off roll on the full-length runway.

As it accelerated the crew realised the twinjet was delivering insufficient thrust, and go-around power was selected at 137kt. The aircraft lifted off and crossed the upwind end of the runway at 276ft.

None of the 216 occupants was injured. British Airways has issued a safety notice to crews highlighting the incident and stressing the need to avoid distraction during calculations, the inquiry states. It is also reviewing data-entry and checking procedures to ensure they have sufficient error traps.