Partnair Flight 394 - Flight

Flight

The Convair 580 aircraft was en route from Oslo Airport, Fornebu, Norway to Hamburg Airport, West Germany. The passengers were employees of the shipping company Wilhelmsen Lines who were flying to Hamburg for the launching ceremony of a new ship. Half of the employees of the company's head office were on board. Leif Terje Løddesøl, an executive of Wilhelmsen, said that the atmosphere in the company was "very very good" prior to the accident flight. He said that some of the employees "maybe" had been to prior naming ceremonies, which he described as "quite exciting." A regular employee on the flight, one of the top-performing employees in the company, had been asked to give the speech during the launching ceremony. Løddesøl said that it was not often that a "normal person" in the company was chosen to read the speech in the naming ceremony.

The flight crew consisted of Captain Knut Tveiten and First Officer Finn Petter Berg. Before the flight the crew found that one of the two main power generators did not work, and the mechanic who inspected the aircraft was unable to fix it. In the Norwegian jurisdiction an aircraft is only allowed to take off if it has two operable sources of power. Also the aircraft's Minimum Equipment List required two operating generators. The first officer decided that he would run the auxiliary power unit (APU) throughout the flight so that the flight would have two sources of power and therefore be allowed to leave. The pilots did not know that one of the three APU mounts was broken, and the resulting vibration would be a factor in the accident flight. The airport refused to let the flight go until the catering bill was paid. Before the aircraft took off, the first officer left the cockpit to pay the catering company.

As the Partnair aircraft passed over the water, a Norwegian-piloted F-16 jet passed by it. The fighter pilot was startled by the sudden appearance of the aircraft and contacted Oslo air traffic control. He believed that the radar data were false and that the aircraft was closer to his jet than his on-board computer had indicated.

As the aircraft neared the Danish coastline, 22,000 feet (6,706 m) over the North Sea, the tail section of the aircraft started to rattle. The broken APU mount vibrated due to counterfeit bolts in the tail of the aircraft, which were weaker than the authentic parts. The investigators concluded that the vibrations reached the same frequency and went into synchronization, a phenomenon known as resonance, causing a coupled harmonics force similar to the one that caused the Tacoma Narrows Bridge collapse in 1940; the force of each vibration wave would add to that of another vibration, increasing in amplitude until the structure failed.

With a rising level of vibration, a failure in the plane's tail section must have become evident to the crew. In the investigation, it was found that the crew triggered the fire extinguisher for the APU. The rudder oscillated to its maximum limits and jammed to the left, and the aircraft was forced into an abrupt left turn that caused the aircraft to roll over. The crew recovered for a brief moment. The rudder jammed to the left again and the shroud doors, which provide mechanics access to weights in the aircraft's tail that control the movement of the rudder, broke off. The aircraft went into a second roll, and the tail section of the aircraft disintegrated. The rest of the aircraft disintegrated on the way down to the sea.