Synopsis
On 12 December 2009, an Airbus A340-642, registration G-VYOU, operated a commercial passenger flight from London Heathrow Airport. During pre-flight preparations, the flight crew inadvertently used the anticipated landing weight of 236.0 tonnes instead of the actual takeoff weight of 322.5 tonnes when requesting takeoff performance data from a central computer via the Aircraft Communications Addressing and Reporting System (ACARS). The resulting takeoff data provided speeds significantly lower than required: a rotation speed (VR) of 143 knots and takeoff safety speed (V2) of 151 knots, versus the correct values of 157 and 167 knots. Additionally, the crew set a FLEX temperature of 74°C, a greater thrust reduction than the correct 63°C. The error went undetected during pre-flight checks, and the aircraft departed using these incorrect settings.
History of the Flight
During the takeoff roll, the pilot flying noted slightly lower acceleration than usual but did not consider it abnormal. The rotation was described as "slightly sluggish and nose heavy." After rotation, the aircraft settled at a speed below the lowest selectable speed (VLS), prompting the pilot to reduce pitch attitude to accelerate. The initial climb rate was between 500 and 600 feet per minute. Flaps were retracted on schedule, and the aircraft continued its climb without selecting full takeoff thrust. Later in the climb, the crew reviewed the takeoff data and realized the mistake. The flight proceeded to its destination without further incident. No injuries to the 16 crew or 282 passengers were reported, and the aircraft sustained no damage.
Standard Operating Procedures
The operator’s standard operating procedures (SOPs) required crews to calculate an estimated takeoff weight based on the final zero fuel weight (ZFW) for an initial takeoff performance request. The procedure included multiple crosschecks, such as writing the actual takeoff weight on the printout alongside the estimated value. In this case, a late change to the ZFW caused the crew to deviate from the normal sequence; they omitted the initial estimate and waited for the actual loadsheet, then inadvertently entered the landing weight in the takeoff weight field. The operator noted that the landing weight (236 tonnes) would have been acceptable as a takeoff weight on the Airbus A340-300, which the crew also flew, possibly explaining why the error was not immediately obvious.
Operator’s Assessment
The operator attributed the incident to time pressure and the disruption caused by the late ZFW change, which led to loadsheet and performance procedures being conducted out of sequence. The crosschecks built into the SOPs were ineffective because the erroneous value was not detected. The operator also highlighted that the Green Dot speed crosscheck, used by some operators to compare separately entered data, was not part of their procedures.
Post-Incident Actions
Following the incident, the airline reiterated correct procedures for entering data into the Multi-function Control and Display Unit (MCDU) and emphasized the importance of independent crosschecks. The format of the takeoff data calculation (TODC) printout was altered to include a warning if a weight below maximum landing weight was entered in the takeoff weight field. The airline initiated a review of TODC and loadsheet procedures and considered implementing a Green Dot gross error check, pending feedback from Airbus. Previous similar incidents, including an AAIB investigation into a Boeing 767 and a BEA report on erroneous takeoff parameters, were referenced. Safety recommendations from an earlier incident involving an Airbus A330 (G-OJMC) were reiterated, calling for takeoff performance monitoring systems.