Investigation Summary
The investigation into Flight 394 is a landmark case in aviation safety regarding Unapproved Aircraft Parts (UAP). Investigators found that three of the four bolts securing the vertical fin to the fuselage were counterfeit. These bolts, which should have been high-strength aerospace grade, were made of inferior steel and lacked the required heat treatment, possessing only about 60% of the required strength. Additionally, the aircraft's Auxiliary Power Unit (APU) was running during the flight due to a faulty generator. The vibrations from the APU, combined with the loose tail section caused by the worn counterfeit parts, led to a resonance phenomenon known as flutter. This flutter became so violent that it destroyed the tail structure, leading to a total loss of control.
Final Conclusions
The primary cause was the structural failure of the vertical stabilizer's attachment points due to the use of counterfeit bolts and sleeves. The failure was exacerbated by vibrations from the APU and the aircraft's aging structure. The accident highlighted a massive global trade in 'bogus' aircraft parts, leading to a major crackdown by the FAA and international regulators.
Video Analysis
The Biggest Airline Disaster In Norwegian History | Blown Apart — Mayday: Air Disaster investigates the crash of Partnair Flight 394 and the shocking discovery of counterfeit parts that led to the disaster.
Watch on YouTube ↗If playback is blocked, the owner has disabled embedding — use the link above.
Systems & Failure Modes
Vertical Stabilizer Attachment
The four-bolt system designed to secure the tail fin to the fuselage; three bolts were found to be counterfeit.
Auxiliary Power Unit (APU)
An onboard generator that provided power; its vibrations triggered the resonance in the weakened tail structure.
Rudder Control System
The structural failure led to the rudder jamming and eventually the entire tail assembly tearing away.
Interesting Facts
- 01The aircraft was 36 years old at the time of the accident.
- 02All 50 passengers were employees of the Wilhelmsen Lines shipping company.
- 03The counterfeit bolts had only 60% of the strength of genuine parts.
- 04The APU was being operated in-flight because one of the two main engine generators was inoperative.
- 05This remains the deadliest aviation accident in Danish territory involving a civil aircraft.
Safety Actions & Advisories
UAP Regulation
The FAA and international authorities significantly tightened regulations and oversight regarding the documentation and traceability of aircraft spare parts to eliminate counterfeit components from the supply chain.
Maintenance Audits
Increased scrutiny of charter airline maintenance records and financial health, as Partnair's financial distress contributed to poor maintenance practices.
Known Controversies & Unanswered Questions
Counterfeit fasteners in the tail
The AAIB/N (Norwegian) investigation established that a significant portion of the bolts securing the vertical stabiliser were substandard or counterfeit, contributing to the loss of the tail. The scope of counterfeit-parts penetration into the aviation supply chain, and how it went undetected, remained a subject of formal follow-up by regulators.
Military wake-turbulence hypothesis
Some analysts and family representatives have raised whether a nearby military aircraft (a US Navy P-3 Orion was reportedly in the general area) could have contributed via wake turbulence, and questioned the completeness of radar-data release. The official investigation concluded structural failure alone was sufficient to explain the accident; the alternative scenario is not supported by the final report but continues to be raised.