Two passengers attempted to stop a British Airways Boeing 777-200 from taking off from a Caribbean airport last September, after realising the crew had lined up at the wrong runway intersection, but were too late to prevent the departure.

The pilots of the twin-jet, bound for Antigua, had intended to depart from the southwestern end of runway 07 - the 'A' intersection - at St Kitts' Bradshaw International Airport.

Despite specifically requesting a departure from 'A', the aircraft mistakenly taxied instead for the 'B' intersection, near the runway's midpoint, leaving available take-off distance of just 1,220m (4,000ft). The take-off performance calculations had been based on a distance of 1,915m.

The oversight escaped detection despite several references and queries in the communications between the crew and air traffic control.

In details of the event released today, the UK Air Accidents Investigation Branch reveals that the carrier's station engineer and airport duty manager were on board the 777 and realised the error as the aircraft lined up on the runway.

The engineer quickly moved from his seat to speak to a member of the cabin crew, telling her that he needed to contact the pilots immediately to warn them the aircraft was wrongly positioned.

In the cockpit the captain had specifically commented that the runway looked short. Neither pilot had been to the airport before and the lack of a tractor meant the crew had taxied the jet from the stand themselves. But, in spite of the captain's concerns, neither cross-checked the jet's location on the runway.

Instead the captain told the co-pilot to "stand on the brakes", says the AAIB, and apply a high thrust setting - some 55% of N1 level - before releasing the brakes for the take-off roll.

In the cabin behind, the station engineer realised that the aircraft was powering up for take-off and abandoned his bid to reach the crew. The 777 accelerated but reached the touchdown-zone markers for the reverse-direction runway 25 by the time it passed the crucial V1 decision speed, and lifted off about 300m from the end of the paved surface.

 St Kitts
 Source: AAIB

Taking off from the 'B' intersection reduces the available distance by 1,110m and the AAIB says that British Airways does not authorise 777 departures from this point on runway 07.

The incident, on 26 September last year, occurred in daylight although the sun was low in the west.

While the AAIB attributes the event to simple lack of familiarity with the airport, combined with disorientation from poor signage, it also underlines the psychological factors which contributed to the failure to identify the error.

Bradshaw is a simple airport, and the crew did not conduct a taxi briefing. The AAIB says that the crew would probably have briefed the route at a larger, more complex airport.

It adds that the crew appears to have suffered from "confirmation bias", noticing only the evidence that backed their mistaken assumption of being at the correct intersection.

Crew resource management training should address this tendency in two ways, says the AAIB: by emphasising the need to "seek evidence that disproves assumptions whenever they are called into doubt" and by providing communications skills needed for "confident and clear discussion" of the problem.

Source: Air Transport Intelligence news