What happened
On 7 December 2003, a Boeing 737-800, registration LN-RPL, was performing a charter flight with a stopover at Göteborg/Landvetter Airport in Sweden. The flight was part of a return service from Salzburg, Austria, to Stockholm/Arlanda. After passengers disembarked in Gothenburg, 121 passengers remained on board for the continuing leg.
During the takeoff roll, as the aircraft approached 80 knots—well before reaching V1—the pilot flying noticed the aircraft's nose was lifting spontaneously without any input on the control column. The co-pilot immediately notified the commander, who took control and aborted the takeoff. Upon returning to the terminal, the crew and ground personnel discovered that the passenger distribution in the cabin did not match the data provided in the loadsheet. The passengers were actually concentrated in the rear of the aircraft, whereas the loadsheet indicated an even distribution.
The investigation
The Swedish Accident Investigation Board (SHK) examined the aircraft's mass and balance data, the loadsheet production process, and the computerized PALCO system used by the operator. The investigation focused on why the loadsheet contained inaccurate passenger positioning data and how the aircraft's center of gravity (CG) was affected. Investigators also reviewed the airline's routines for handling non-routine flight segments and the reliability of automated loadsheet systems.
Findings
- The aircraft was operating with a center-of-gravity position at more than 1/4 aft of the certified CG span.
- The loadsheet provided to the pilots incorrectly stated that passengers were evenly distributed, when in fact most were seated in the aft portion of the cabin.
- The PALCO system used a default value for passenger distribution when specific seating information was not received, and the system's notification of this default was not sufficiently clear.
- Shortcomings existed in the routines and computerized systems used for producing loadsheets.
- The spontaneous nose lift occurred at approximately 80 knots, which is significantly lower than the normal rotation speed of approximately 140 knots for this mass.
Safety action
The investigation led to recommendations for the Swedish Civil Aviation Authority to:
- Increase international demands for the quality assurance and human factors validation of operational aid systems.
- Require that computer systems used for flight planning explicitly notify pilots when a calculated or default value is being used instead of a verified value.
- Implement a requirement for physical checks of passenger seating against loadsheet data for all heavy aircraft passenger traffic.