What happened
On December 10, 2006, a Corsair Boeing 747-400, registration F-HLOV, was preparing for a long-haul flight to the West Indies from Paris-Orly airport. During the pre-flight preparations, the crew was managing several technical items, including a fuel scavenge pump tolerance and an ongoing hydraulic system repair.
While calculating takeoff parameters using a Boeing Laptop Tool (BLT), the commander inadvertently turned off the device, erasing the previously entered data. During the subsequent re-entry of information, the commander mistakenly entered the Zero Fuel Weight (ZFW) instead of the Takeoff Weight (TOW). This error resulted in a calculated takeoff weight of 242.3 t instead of the actual 341.3 t. Although the commander noted an unusual thrust value, the discrepancy in takeoff speeds was not identified by the crew.
The aircraft performed a rolling takeoff. Due to the incorrect weight calculation, the aircraft's acceleration was abnormally low. During the rotation phase at approximately 132 kt, the pilot flying noticed the aircraft felt heavy and increased the pitch to 13 degrees. During this maneuver, a ground vehicle observed smoke on the runway and alerted air traffic control.
Following the takeoff, the crew suspected a calculation error and decided to increase all retraction speeds by 20 kt. While climbing through FL180, the crew was notified of debris and a streak on the runway. Fearing a tail strike, the crew performed the abnormal checklist and returned to Orly. A subsequent inspection by a chase plane revealed scrapes on the lower fuselage near the APU compartment.
The investigation
The investigation focused on the sequence of data entry into the BLT and the FMS. It was established that the crew used the BLT to calculate performance based on environmental conditions and existing maintenance tolerances. The investigation examined the interaction between the crew members during the data entry process and the failure to detect the significant discrepancy between the entered ZFW and the actual TOW.