French investigators have detailed a weight data error which resulted in a Boeing 777 freighter commencing an underpowered take-off at Paris Charles de Gaulle last month.

The Air France aircraft weighed 343t at the time of departure but investigation authority BEA states that the crew carried out performance calculations using a weight of only 243t.

These speeds, used by the flight-management system, resulted in insufficient power being applied during the take-off roll.

The 777F has a payload capability of 102t and a maximum take-off weight of just under 350t, showing that the Air France jet was almost fully-laden for the 22 May service to Mexico City.

BEA says that the crew realised, during rotation, that the aircraft was not climbing. The pilots limited the 777F’s pitch and applied full go-around thrust.

Surveillance data indicates that the aircraft departed runway 26R which has a length of 4,215m (13,830ft).

BEA says that the aircraft (F-GUOC) continued to its destination without further incident.

While investigators have yet to reach conclusions over the event – including an analysis of data-check procedures – the 100t weight error is reminiscent of a similar miscalculation involving an Emirates Airbus A340-500 departing from Melbourne in March 2009.

The inquiry determined that the aircraft’s weight of 362.9t had probably been miskeyed as 262.9t during take-off performance calculations on the electronic flightbag.

While rolling for take-off the A340 did not deliver adequate thrust for its actual weight and, having used almost the whole runway, the jet eventually over-rotated and sustained a series of tail-strikes before overrunning. It managed to become airborne and returned to land safely.

Australian Transport Safety Bureau has carried out in-depth research into the problem of data errors.

Its analysis has highlighted potential problems with mixed-fleet flying, which exposes crews to multiple aircraft weight ranges and makes unusual figures more difficult for pilots to detect. It also states that pilots have become less able to perform ‘rule of thumb’ estimates to check whether calculated performance data is reasonable.

Source: Cirium Dashboard