Flight Details
Partnair Flight 394, operating as PAR 394, was a charter flight scheduled to depart from Oslo to Hamburg on September 8, 1989. The aircraft, registration LN-PAA, was originally scheduled for departure at 1500 hours. However, delays occurred due to a credit suspension by the Civil Aviation Administration, Norway (CAA/N) and the catering company. The financial issue was resolved, and the crew received permission to depart.
Technical Issues
During the period from September 6 to 8, 1989, LN-PAA experienced intermittent technical problems with the left AC power system. The AC generator was replaced, but the malfunction persisted. For the flight to Hamburg, the crew decided to use the APU generator as the electrical power source for the left AC system.
Sequence of Events
The aircraft took off at 1559:50 hours. It proceeded normally to the planned cruise level of flight level (FL) 220. At 1604 hours, PAR 394 was cleared direct to the AAL VOR/DME (Aalborg). As the aircraft climbed through FL 180 at 1616 hours, Oslo ACC informed the crew of strong westerly winds at altitude and suggested a 100-degree heading change to the right. At 1622 hours, PAR 394 was informed that radar service from Oslo ACC was terminating and that the flight would enter Danish-controlled airspace in two minutes, after which they were requested to contact Copenhagen ACC.
According to the Flight Data Recorder (FDR), LN-PAA reached its cruising level at 1623 hours. Half a minute later, the crew established contact with Copenhagen ACC, reporting that they were maintaining FL220. Copenhagen ACC confirmed radar contact. This was the last radio communication with PAR 394. The next control point was AAL VOR/DME.
The flight appeared to proceed normally until the air traffic controller at Copenhagen ACC observed unexpected right turn on radar, followed by the disappearance of the radar signal. At 1640 hours, the controller attempted to contact PAR 394 but received no reply. Multiple attempts followed. At 1642 hours, air traffic services in both Denmark and Norway initiated a search. At 1659 hours, rescue authorities in Norway and Denmark were informed. The aircraft was not found, and it was confirmed that a serious accident had occurred. None of the 55 persons on board survived.
Probable Cause
According to the official investigation, the accident was caused by loss of control due to the destruction of primary control surfaces in the tail section, which, in turn, was caused by aeroelastic oscillations initiated by abnormal clearances in the vertical stabiliser attachments to the fuselage structure. The condition of the attachments was a result of excessive wear in pins and sleeves used in this structural joint. The pins and sleeves were of an inferior quality and did not satisfy specified values for hardness and tensile strength. They had also been installed and inspected using sub-standard maintenance procedures. Undamped oscillations in the elevator contributed to the structural failure of the empennage.