What happened
On 12 December 2009, an Airbus A340-642, registration G-VYOU, was involved in a serious incident during departure from London Heathrow Airport. Following a late change to the zero fuel weight, the flight crew performed loadsheet and performance procedures out of their usual sequence.
When requesting takeoff performance data via the Takeoff Data Calculation (TODC) system, the crew used the expected landing weight of 236.0 tonnes instead of the actual takeoff weight of 322.5 tonnes. This error resulted in the aircraft being programmed with a rotation speed (VR) of 143 kt and a V2 speed of 151 kt, both of which were significantly lower than the required 157 kt and 167 kt. Additionally, the thrust setting used a 'FLEX' temperature of 74°, which was higher than the correct value of 63°.
During the takeoff roll, the pilot flying noticed sluggish acceleration and a heavy nose during rotation. The aircraft settled at a speed below VLS, prompting the pilot to adjust the pitch to accelerate. The rate of climb was also noted to be low, between 500 and 600 fpm. The crew eventually identified the error in the TODC data during the climb.
The investigation
The AAIB investigation established that the crew's departure from standard operating procedures (SOPs) was driven by time pressure following the late weight change. Because the crew opted to wait for the final loadsheet rather than using an estimated takeoff weight for an initial request, they bypassed the opportunity for a gross error check between the initial request and the final loadsheet.
While the crew did notice the unusually high FLEX temperature, this did not trigger a verification of the TODC values. The investigation also examined the airline's performance calculation systems, noting that the error was not caught by the existing multi-layered crosschecks during the pre-flight phase.
Findings
- The crew used incorrect takeoff speeds and reduced thrust due to entering the landing weight instead of the takeoff weight in the TODC request.
- Time pressure and the late change in weight led the crew to perform loadsheet and performance procedures out of sequence.
- The lack of an initial TODC request using an estimated weight prevented a primary error-detection mechanism from functioning.
- The crew's internal crosschecks were ineffective in identifying the discrepancy in the performance data.