Introduction

On Friday, September 8, 1989, at 16:39 local time, a Convair CV-580 with registration LN-PAA crashed in the Skagerrak, just north of Hirtshals. The aircraft was en route from Oslo Fornebu to Hamburg with 50 passengers and 5 crew members on board. There were no survivors.

It was a charter flight for Wilhelmsen, operated by Partnair, and the flight had the route number Partnair 394. After approximately three years of investigation, the Accident Investigation Board for Civil Aviation concluded that the accident was caused by flutter in the tail control surfaces, induced by counterfeit parts in the aircraft's rudder. Flutter is a self-reinforcing vibration that occurs when aerodynamic forces and structural oscillations amplify each other. According to the accident investigation board, the vibrations built up gradually, without the crew being able to detect them, until the tail control surfaces ultimately disintegrated.

This conclusion has stood for 36 years, despite numerous objections to the accident investigation board's conclusion having been raised over the years.

Background to This Report

Approximately nine minutes before the Partnair aircraft disappeared from radar, a Norwegian F-16 fighter jet passed at supersonic speed directly towards the Partnair aircraft at the same altitude. The accident investigation board considered this close pass and concluded that it occurred too long before the accident to have had any connection.

This report shows that the accident investigation board's timeline is incorrect. The Flight Data Recorder shows that deviations in the Partnair aircraft's speed and heading began as early as 6 minutes before the aircraft hit the water—coinciding with the time of the F-16 pass. The accident investigation board interpreted these deviations as normal and limited its analysis to the final minute of the flight.

In addition, a review of the radar data shows that these have been altered after recording. The datasets from Mågerø and Skagen contain physically impossible situations, have been delivered in multiple versions with mutual discrepancies, and bear clear traces of manual manipulation. The radar data cannot be used as evidence for where the aircraft were in relation to each other.

Furthermore, several significant findings from the technical investigation were not addressed in the accident report. RARDE in England found, among other things, a hole in a shelf plate inside the aircraft, caused by a fragment travelling at 650 m/s—a velocity that cannot be achieved without an explosion. Trace amounts of the explosive RDX were found on two separate aircraft parts, molten iron that had solidified in the air, and traces of brief heating on interior parts. These findings were withheld from the public.

Purpose

The purpose of this report is to verify the accident investigation board's conclusion by analysing available documentation, including the Flight Data Recorder, radar data, and technical reports that have not been publicly available.

The report is not written to assign blame, but to highlight weaknesses in the investigation and to show that an alternative explanation—that a supersonic shock wave from the F-16 close pass damaged the Partnair aircraft's tail control surfaces—is a far simpler and more probable cause than the one the accident investigation board relied upon.

Structure of the Report

The report is structured so that each chapter illuminates one aspect of the accident:

Background provides an overview of the flight, the aircraft type, and the circumstances surrounding the accident.

Airspeed shows that the accident investigation board misread the Flight Data Recorder by approximately 15 knots in speed, which has affected their analysis of the sequence of events.

Navigation addresses the pilots' navigation plan and the course deviations prior to the accident.

Flight Data Recorder shows that the deviations in the aircraft's parameters began at the time of the F-16 pass—six minutes before the aircraft departed controlled flight—and that these deviations are consistent with a systematic troubleshooting process on the part of the crew.

Shock Waves describes the physical mechanism behind supersonic shock waves and how these can inflict structural damage on an aircraft.

APU shows that the loose APU unit in the tail, which the accident investigation board emphasised as a contributing factor, most likely came loose as a consequence of the accident—not as a cause.

The Close Pass addresses the two opposing F-16 fighter jets and explains the motivation for the Norwegian crew to carry out a close pass.

The Merge explains why the F-16 pilot's merge manoeuvre against a slow-moving propeller aircraft may have resulted in a significantly closer pass than intended, and how the shock wave geometry strikes the rudder's trim tab from the side.

Emergency describes a potential sequence of events from the moment something went wrong until the aircraft hit the water, based on the Flight Data Recorder and established flight operations knowledge.

Radar Echoes of Wreckage analyses Swedish radar observations of objects that separated from the aircraft, and shows that the accident investigation board's hypothesis about honeycomb cannot be correct.

Radar Data and Radar Analysis review the radar datasets from Mågerø, Skagen, and AWACS. The analysis reveals physically impossible situations, speed differences that cannot be explained by radar precision, time discrepancies that apply only to the F-16 data, and that the datasets have been delivered in multiple versions with manually introduced corrections.

Evidence That Was Not Examined presents findings from the RARDE reports and other technical investigations that have not been publicly available, including high-velocity fragments, RDX traces, sooted parts, and molten metal, as well as an analysis of the propellers indicating that the left propeller separated from the engine before the aircraft hit the water.

Concluding Remarks compares the two hypotheses and reflects on the investigation process and the need for transparency.