Concluding Remarks

Hypotheses

Occam's Razor

Occam's Razor is a principle that states the simplest explanation—the one requiring the fewest assumptions—is generally the correct one. If one compares the accident investigation board's causal hypothesis of "counterfeit parts" with a hypothesis that a shock wave from an F-16 close pass caused the accident, it is the latter that is built on far fewer premises.

The accident investigation board chose to narrow its focus area and limit the analysis to only a small segment of the sequence of events. By regarding large parts of the sequence as "normal," the accident investigation board ignored essential information that weakens the hypothesis that the accident was caused by counterfeit parts. Despite the fact that the accident investigation board skipped over a large portion of the sequence of events, they were unable to put forward a simple causal hypothesis. Approximately 10 pages of the report are devoted to detailed descriptions of how the damage must have occurred.

The main premise of the counterfeit parts hypothesis is that vibrations built up over time, from zero vibration to catastrophic oscillations in the control surfaces. Despite the fact that a pilot will feel even small vibrations in the controls during those parts of the flight that are flown without autopilot, the accident investigation board maintains that it was only around one minute before the accident that the pilots discovered something was wrong. At that stage, it was probably too late to save the aircraft, as the damage had developed too far.

Gradually increasing vibrations in the tail, which propagate through the aircraft's control linkages, would be detectable by the pilots. A loose APU in the tail, "banging" against the fuselage or creating abnormal vibrations, would be audible and palpable to the crew in the cabin—and most likely to the pilots as well.

The hypothesis that the emergency came so suddenly that the crew did not know what was happening seems entirely improbable.

A Simpler Sequence of Events

The sequence of events can to a far greater extent be explained by a simpler hypothesis:

After "top of climb," LN-PAA encounters an F-16 at the same altitude. A small dot on the horizon grows gradually larger, but is virtually impossible to see without radar. The F-16 pilot has probably just passed one of the two oncoming Viper aircraft (Viper 20 and 71), and assumes that the Partnair aircraft approaching is the last of the fighter jets. In reality, both Viper aircraft have already passed. The F-16 pilot initiates a "merge"—a standard manoeuvre in which one passes an oncoming aircraft and begins a turn to get in behind the other aircraft. The AWACS video confirms that the F-16 turns to the left after the pass, which is consistent with the initiation of such a manoeuvre. The F-16 pilot did not complete a full merge with subsequent aerial combat, but continued towards Rygge after the turn.

A merge against a slow-moving propeller aircraft, instead of a fast fighter jet, may cause the F-16 pilot to misjudge the distance and pass much closer behind the Partnair aircraft than intended. When the F-16 turns behind the Partnair aircraft, the supersonic shock wave will strike the Partnair aircraft's tail control surfaces from nearly a 90-degree angle from the side—the angle that provides the greatest possible impact surface area and thus the greatest possible damage potential.

At 500 metres per second, the aircraft pass each other—so fast that the crew of LN-PAA have no chance of seeing the F-16, but they hear the crash of the supersonic shock wave striking the aircraft's fuselage. The aircraft has until now been functioning normally, but now it apparently loses speed and begins to fly uncoordinated. The crew makes several small reductions in speed, probably in connection with troubleshooting the problem. The damage to the rudder gradually worsens. When the crew finally understands that there is structural damage to the aircraft, it is too late. The aircraft rolls and immediately enters a dive. Speed increases rapidly, causing flutter to develop.

Without the crew managing to regain control of the aircraft, the dive continues downward and the flutter situation worsens. Eventually, the control surfaces and tail section disintegrate, and there is no longer any possibility of regaining control. The aircraft bunts and the wings break off. The aircraft continues an uncontrolled descent towards the sea surface. It is still affected by aerodynamic forces, but without any directional stability, it constantly changes direction and no longer behaves like a normal aircraft. In addition to flying unpredictably, it continuously loses altitude and flies downward towards the sea in an area where warships are present that undoubtedly follow the situation on their radars and attempt to understand what the unidentified object is, and whether it constitutes a threat.

For Reflection

In aviation, accidents and serious incidents are investigated to find the cause. When the cause is clear, regulations can be improved. This has produced an evolutionary development of laws and regulations, and the result is that it has steadily become safer to fly. The technical safety systems have become ever more advanced, and several of them have over the years become mandatory to use during flight.

Had the incident occurred today, the Traffic Collision Avoidance System (TCAS) would have ensured that both the Partnair pilots and the F-16 pilot received a warning when the aircraft were about to come too close to each other. Unfortunately, the aircraft were not equipped with TCAS in 1989.

Rules do not help if they are not followed by everyone in the aviation industry. Safety is based on many layers of protection. It is only when there are concurrent breaches in all the safety layers that things go wrong. Since several layers of safety can be breached simultaneously by a single action, it is important that all parties are extremely careful not to break any of the rules.

The Investigation Process

The accident investigation board's investigation process must be transparent, and its conclusion verifiable. To be able to verify the conclusion, one must have access to all documentation. Improved aviation safety is in practice only achieved if regulations are changed so that corresponding accidents are prevented.

Both the accident investigation board and the Armed Forces were involved in the investigation of the Partnair accident. In the documentary «Partnair – The Forgotten Tragedy,» it emerges that the accident investigation board and the Armed Forces are reluctant to grant access to the case documents or be of assistance in verifying the accident report's conclusion. The argument is that the accident has already been investigated and that the accident report "stands on its own legs." (Wisting, 2023)

It is easy to be impressed by the report's length and the extensive technical analyses. There are nevertheless several obvious and fundamental weaknesses that could have been avoided had the accident investigation board employed scientific methods correctly. If one does not content oneself with skimming the report, but also scrutinises the accompanying data, fundamental errors become apparent. When the conclusion is built on a series of premises and hypotheses, it all collapses like a house of cards when the basic premises are false.

If one were to use a chair as an analogy, it can hardly be said to stand steady on its own legs. The conclusion that the accident was not caused by any external influence, but by silent, imperceptible vibrations that did not affect the aircraft's instruments, yet tore apart the aircraft's tail structure before the pilots had time to follow the reflex to reduce engine power—seems extremely improbable. With this conclusion, the accident report is at best a wobbling chair that has miraculously remained upright on its single leg.

It is cause for concern when an investigating body, whose purpose is to help improve aviation safety, uncritically relies on information and assistance from a party that was involved in the lead-up to the accident.

Responsibility

Although it is possible to make a probable case for what may have been the triggering factor of the accident, it is important to understand that there was a long series of coinciding circumstances that resulted in the fatal sequence of events. Directing the spotlight towards a single individual or actor alone is not constructive. No one deliberately did anything to expose others to danger—neither the pilot, the airline, the air traffic service, nor the Civil Aviation Authority. Sometimes coincidences cause something to go extremely wrong. Such was the case with the Partnair accident.

It may feel best to single out a scapegoat for the accident, but when many factors have had an impact, it is wrong to point to only one thing. If one is to point to anything at all, it must be the investigation process, which even after an entire generation is still not particularly transparent.

Aviation is safer now than in 1989, both as a result of the Partnair accident and many other aircraft accidents. The development of the civilian regulatory framework is open for all to see, but the Armed Forces are far less transparent. Hopefully, the Armed Forces also change their internal rules and procedures in the aftermath of an accident or serious incident.

What If

Had there not been a focus on engine problems prior to the trip to Hamburg, or had the departure not been delayed, or had Viper 20 and Viper 71 not flown the same route a few minutes ahead of the Partnair aircraft—then LN-PAA would most likely have landed safely in Hamburg on Friday afternoon, 8 September.

Even with damage to the rudder, things could have turned out well had the crew of LN-PAA quickly understood that there was structural damage to the aircraft. They would then have immediately pulled the throttle back to idle, reduced the speed, initiated a descent, and set course for the nearest airport. They would then have transmitted a mayday call on the radio and entered the emergency code 7700 on the transponder.

This would have immediately given them the air traffic service's full attention, and on all radar screens it would have lit up that LN-PAA was in an emergency. The air traffic service would have cleared away other traffic in the air and stopped all movements at the airport in anticipation of an emergency landing. The crew of LN-PAA would have continuously received the controllers' assistance to navigate to the airport, and would have been given clearance to land on all available runways to give the crew the greatest possible freedom of action.

While the aircraft was still in the air, ambulances from across the district would be directed towards the airport to be in disaster readiness. All available rescue personnel and vehicles would have been in position by the runway, ready to reach the aircraft within seconds of it coming to a stop.

All of these procedures have been developed over several decades, after the causes of fatal aircraft accidents have been identified. Many passengers are completely unaware of how fortunate they are when the procedures prevent a serious accident. Those who were in the air over the Skagerrak on the day of the accident were unfortunately not as fortunate.

Left behind are hundreds of family members, friends, and colleagues. Many are still affected by the accident and have a need for greater openness about what happened.