Foreword

Aviation is a vital part of society, and thanks to a sustained focus on safety and thorough investigation of accidents and incidents, the likelihood of perishing in an aircraft accident today is extremely low. This presupposes, however, that investigations are independent and that they identify the actual cause.

When the Partnair accident occurred on September 8, 1989, new legislation governing accident investigations had recently been enacted. Previously, a dedicated investigation commission—in which the police were also represented—was established following each aircraft accident, and the work was primarily carried out by individuals affiliated with the Armed Forces. Under the new legislation, a permanent accident investigation board was established, in which the police were no longer represented. Arnstein Øverkil, who had previously served as the police's permanent representative on investigation commissions, instead led the police's own criminal investigation of the Partnair accident in his capacity as Chief of Police in Asker and Bærum. The police and the accident investigation board serve different purposes in their investigations: where the police look for potential criminal offences, the accident investigation board's task is to determine the cause of the accident in order to improve regulations and prevent future accidents.

Background and Motivation

I hold a Cand. Scient degree in computer science and have worked for over 30 years in the development of IT systems. This background has given me experience with systematic analysis of complex interrelationships. In 2010, I obtained a private pilot licence (PPL), which has provided me with a fundamental understanding of aviation and flight operations.

I began my investigative work after watching the documentary series Partnair – Den glemte tragedien (Partnair – The Forgotten Tragedy), which aired on Viaplay in the autumn of 2023. I lost my own father in the Partnair accident when I was 13 years old, and the documentary series provided me with certain new information that awakened a strong desire to understand what actually happened.

Based on what I have found through this work, I am convinced that the official accident report has arrived at an incorrect cause determination. Rather than merely questioning the accident report, I wish to demonstrate why the conclusion cannot be correct—and thereby highlight how important it is that this accident is reinvestigated.

Purpose and Scope

My goal has been to document my analyses and conclusions in order to communicate these to journalists, next of kin, and others who wish to gain a better understanding of the case. This document is not to be regarded as an alternative accident report. It is a working document, and I do not claim that it is free of errors. Its purpose is twofold: to identify the weaknesses in the official accident report and to show which of its hypotheses are built on false premises. In addition, I put forward alternative hypotheses and show which observations and findings support them.

Sources and Documentation

My work is primarily based on documentation released by the police and the accident investigation board. I quote from these documents in the report but am not at liberty to publish them in their entirety. It is worth noting that several of the reports from the investigation work have been subject to classification, which has made it considerably more difficult to scrutinise the accident investigation board's conclusions—and which is a contributing reason why these weaknesses have not been uncovered earlier.

Methodological Approach

My approach has been to analyse as much as possible of the documentation from the original investigation. By reviewing the basis for the investigation reports, I have sought to verify the accident investigation board's conclusions. The board built its cause determination on a series of premises. By challenging these premises, one can assess whether the conclusion stands on solid ground, whether it wavers—or whether it collapses entirely.

The work has followed a systematic approach: formulating hypotheses, and then using data, observations, and findings to either strengthen or reject them. Through this process, I have arrived at hypotheses that can substantiate the sequence of events in this case.

An important principle in this work is Occam's razor: the simplest explanation compatible with all known facts is, as a rule, the correct one. If a hypothesis requires a long series of assumptions to hold, it is less likely to be correct than a hypothesis with few assumptions. This principle has been very useful in a case where it is possible to put forward many complex hypotheses. Rather than being carried away by complexity, it is important to focus on the simple explanations—precisely because these are most likely to be correct.

«Occam's razor (Latin: lex parsimoniæ, 'the law of parsimony') is a problem-solving principle in the philosophy of science. The principle holds that among two possible hypotheses (or explanations), all other things being equal, the simplest is most likely the correct one. The principle states that one should not operate with more assumptions than are needed to explain what is observed.» (Ockhams barberkniv, Wikipedia)

Findings

Personally, I prefer simple explanations over complex hypotheses with many dependencies and assumptions. Several of the hypotheses presented in this report coincide with hypotheses that have been put forward numerous times over the years. Through my analysis, however, I have also made new findings that I have not seen discussed previously. Several of these findings strengthen hypotheses about a sequence of events that is far simpler than what the accident investigation board assumed. In addition, there are some new findings that lead me to put forward hypotheses that some will perceive as controversial. These hypotheses are supported by concrete findings, not vague assumptions.

My work has led me to realise that the accident was caused by a long series of coincidences, and that it is also a series of coincidences that has contributed to the cause not being found long ago.

I cannot claim that I am one hundred per cent certain that I have found the full and complete truth. But I present what I believe is important for understanding the case, and my wish is that this work will be of help to others who wish to continue working on it.

Finally, I wish to emphasise: just because something seems unthinkable and improbable does not mean it is impossible. It is logical reasoning and hypotheses strengthened by concrete findings that underpin what I present.

Acknowledgements

Special thanks to Alexander Wisting. Without the work he has carried out over many years on the TV documentary Partnair – Den glemte tragedien (Partnair – The Forgotten Tragedy), published in 2023, I would never have begun looking into this case. We have collaborated closely since the documentary was released, and I have continuously shared my analyses with him as this document has taken shape. I greatly appreciate that Alexander has never given up on this case. In order to achieve the goal of having this case reinvestigated, it is essential that the information reaches as many people as possible—and that is difficult to accomplish without the media.

I also wish to thank Jorunn Steinmo, who contacted me in the spring of 2025 and helped obtain additional documentation. Without this assistance, it would have been difficult to understand what happened to the Partnair aircraft after it departed controlled flight and flew uncontrollably towards the sea.

Great thanks are also extended to Hans Arnegard for much valuable and invaluable help. There is scarcely anything about the Convair 580 that he cannot answer or find the answer to in all the binders he has from his time as a pilot, mechanic, and instructor for both pilots and mechanics on this aircraft type.

I wish to thank Oslo Police District, which has assisted in locating, digitising, and providing access to documentation related to the case. Without this help, it would have been far more difficult to scrutinise the accident investigation work carried out in the aftermath of the accident.

Finally, I wish to extend the greatest thanks to my family. This case has, since the autumn of 2023, consumed an enormous amount of my time, and I have at times been very absent. It has been so important to me to get to the bottom of why my father perished, and why the truth about this case has not come to light, that I have at times buried myself completely in the work. Thank you for your patience and support.

Hosle, June 2026

Lars Preben Sørsdahl