Paramètres de décollages : risque d'erreur

Regulators worry about take-off performance miscalculation
By David Learmount

The UK Air Accidents Investigation Branch has called for regulators to develop safeguards to prevent take-off performance miscalculations. The AAIB argues that they happen too often and the potential consequences are serious.

It recommends to the European Aviation Safety Agency that it should provide specifications for a take-off performance monitoring system (TOPMS) and require it to be fitted to airliners.

The AAIB's recommendations were sparked by its investigation of a serious incident on 28 October 2008 involving a Thomas Cook Airlines Airbus A330-200 (G-OJMC) that took off from Sangster International airport, Montego Bay, Jamaica for the UK. The commander had quickly selected take-off/go-around power when the aircraft failed to unstick at the calculated rotate speed.

The board says it could not determine the actual error that caused the take-off performance miscalculation, but the effect was as if a much lower weight than the actual take-off mass was entered, because the calculated decision and rotate speeds were too low.

The crew were also carrying out a "flex" take-off, using a de-rated thrust level that was calculated, along with the take-off speeds, on a computer at Thomas Cook's base flight dispatch unit, using figures passed by the crew.

Runway 07 at Sangster was long enough, with an accelerate/stop distance of 2,724m (8,930ft) for a safe take-off to be made, the AAIB says. Its report also cited several other examples of take-off performance miscalculation, including the October 2004 fatal MK Airlines Boeing 747 freighter crash at Halifax, Nova Scotia and several others that involved tailstrikes during take-off.

In addition, the AAIB says it found 26 "relevant events" in its own mandatory occurrence report database.

The AAIB has made two recommendations to EASA: the first is that it should "develop a specification for an aircraft take-off performance monitoring system that provides a timely alert to flightcrews when achieved take-off performance is inadequate for given aircraft configurations and airfield conditions". The second is that it should mandate the fitting of such a device in transport category aircraft.