Description

On 7 December 2003, a Boeing 737-800 being operated by SAS on a passenger charter flight from Salzburg, Austria to Stockholm Arlanda with an intermediate stop at Goteborg made a high speed rejected take off during the departure from Goteborg because of an un-commanded premature rotation. There were no injuries to any occupants and no damage to the aircraft which taxied back to the gate.

Investigation

An investigation into the Incident was carried out by the Accident Investigation Board Sweden. It was found that the airline was operating a series charter flight from Salzburg to Stockholm with an intermediate stop at Göteborg to allow 59 of the passengers to leave (but none to join). After this, 121 remained. Whilst on the ground at Goteborg, the cabin crew noted that most of the remaining passengers were sitting towards the back of the cabin. This was pointed out to the commander, who decided not to take any action until he had seen the loadsheet. When this arrived, it showed that the passengers were evenly distributed in the cabin and that the mass and balance limitations in force were met. The First Officer had been designated PF. After the take off roll commenced, as the aircraft was approaching 80 knots, PF noted that aircraft nose was lifting spontaneously without him moving the control column. He advised the aircraft commander who took over the control and rejected the takeoff.

It was easily discovered once back at the gate that the passenger distribution shown on the load and trim sheet was not where the passengers were actually sitting. As a result, the aircraft centre of gravity was significantly aft of the allowable limit at 38 % MAC, compared to the 25% MAC shown on the load and trim sheet and which had been the determinant of the stabiliser trim setting for take off.

The Investigation examined the application of the standard SAS system for load and trim sheet production in respect of the incident flight and found that it was fundamentally flawed as well as vulnerable to errors of sequence that could - and did - easily arise. It also noted the aircraft commander, having received a helpful but not-required communication from the cabin crew about a passenger loading distribution which was clearly abnormal, had forgotten about this by the time the loadsheet and its stated balance of passenger distribution arrived and he accepted it as presented. It was also noted that the SAS Quality Assurance system had completely failed to identify structural shortcomings in the SAS system for load and trim sheet preparation.

The formal statement of cause produced by the Investigation was that it was caused by “shortcomings in the routines and computer systems used in the production of loadsheets.”

Safety Recommendations

As a result of the Investigation, three Safety Recommendations were made to the Swedish Civil Aviation Authority:

• to seek in international air safety work to ensure that the supervisory authorities concerned place higher demands on the quality assurance, including verification and validation, with reference also to human factors, of operational aids systems that can affect flight safety (RL 2005:20e R1)

• to require information and acknowledgement anytime a calculated or default value is used instead of a verified value for computer systems used by pilots for planning purpose and affecting flight safety (RL 2005:20e R2)

• for all passenger traffic with heavy aircraft, to introduce a requirement for physical checks of passenger seating throughout the cabin versus loadsheet data where computerised systems are used in the production of loadsheets (RL 2005:20e R3)

The Final Report of the Investigation was published on 29 September 2005 and may be see in full at SKYbrary bookshelf: Report RL 2005:20e

Further Reading

• Aircraft Load and Trim
• Passenger Cabin Loading
• Rejected Take Off
• Cross-checking Process