What happened
On March 4, 2010, a China Airlines B747-400F, registration B-18723, was preparing for a departure from Anchorage International Airport, bound for Taoyuan International Airport. During the pre-flight preparation, the crew utilized the ACARS Runway Analysis System (RAS) to determine takeoff performance. However, during the data entry process, the takeoff weight from the computer flight plan was mistakenly used as the takeoff weight for the runway analysis, rather than the actual calculated weight.
As the crew entered performance data into the Flight Management System (FMS), the takeoff speeds (V1, VR, and V2) displayed as dashes ("---"). The crew, unable to identify the cause of the display error, decided to proceed using the takeoff speeds provided by the ACARS RAS. During the takeoff roll, the aircraft rotated at a speed lower than required for its actual weight. This resulted in an excessive pitch angle and angle of attack, causing the rear fuselage to contact the runway.
Following the rotation, the crew experienced a stick shaker warning. The pilot responded by manually increasing thrust to maximum, which helped the aircraft stabilize and continue the climb. After landing at the destination, maintenance inspections revealed significant damage to the lower fuselage skin.
The investigation
The Taiwan Transportation Safety Board (TTSB) investigated the discrepancy between the takeoff weight used in the RAS and the actual weight recorded in the load sheet and computer flight plan. The investigation examined the FMS display errors, the crew's use of the Runway Analysis Manual (RAM), and the decision-making process regarding the potential tail strike. The investigation also reviewed the crew's fatigue levels and the adequacy of the airline's procedures for verifying ACARS-derived performance data.