2018 Ju-Air Junkers Ju 52 crash

Investigation

The accident was investigated jointly by the Swiss Transportation Safety Investigation Board (STSB) and the cantonal police of Grisons on behalf of the federal and cantonal prosecutors' offices.

A spokesperson for the STSB said that the Junkers "fell like a stone to the ground", and that the heatwave in Europe could have been a factor in the crash, as heat reduces an aircraft's climb performance. The police indicated that no distress signal was received from the aircraft prior to the crash. Investigators ruled out a collision with a cable or another aircraft, and said that there was no indication of foul play or the aircraft losing parts before the crash. The aircraft was not fitted with any flight recorders, as they were not required due to the age of the aircraft. Investigators hoped to find some relevant information from passengers' personal photographic and video recordings during the sightseeing flight. The STSB issued its preliminary report on 15 August 2018. An intermediate report was issued on 20 November 2018, citing anterior corrosion marks and cracks, not related to the accident, which effectively grounded the two remaining Ju-52 of Ju-Air (HB-HOP and HB-HOS) until further investigation of these airframe and engine issues.

In August the SonntagsZeitung newspaper published excerpts from a leaked draft of the investigation report, which said: the pilots flew into a high-altitude alpine valley without a safe possibility of turning back; the accident pilots were already known for questionable decisions; and even on check flights, one of the pilots ignored the minimum altitudes. Other causes such as technical failures had been ruled out.

Cause of stall

The investigation confirmed that the aircraft crashed onto the plateau due to stall, which happened due to multiple factors including inappropriate decisions that had been made by the crew and were aggravated by the hot and high condition. Environmental factors played a big role in the crash as the crew's intention to take the scenic route, which involved flying near the Piz Segnas, caused changes on the external condition that threatened the safety of the flight. The decision to fly through the risky route, however, was already shaped by the lack of safety culture and routine violations by the crew and the company itself.

The crew wanted the passengers to get a clearer view of the terrain. To do that, the crew had to lower their altitude and by doing so the necessary distance between the aircraft and the ground for a recovery became limited, hence it became a safety risk. The pilots also decreased their airspeed, flying merely at 100 kn. The clear sky condition and high elevation of the area also altered the aircraft's performance due to the lowered air density. While the aircraft neared terrain, the flight encountered turbulence, a common phenomenon in mountains. Included in the turbulence were updrafts and downdrafts which would significantly affect the aircraft's angle of attack.

During the turbulence, the aircraft was struck by a downdraft which pushed the nose down, causing the aircraft to lose its altitude. The crew then tried to stop the descent by making a nose up input. The pitch eventually stayed above flight level, however, the downdraft suddenly dissipated seconds later. The pilots had been trying to arrest their descent by making a nose up input and the sudden updraft caused the aircraft to pitch up, affecting the airspeed by decreasing it to a level dangerously close to the aircraft's stall speed. As the aircraft was turning to the left when it was struck by the updraft, added by the low speed and the design of the aircraft, the left wing stalled and caused the aircraft to bank heavily towards the left.

Recognizing the situation, the crew tried to recover the aircraft by intuitively turning towards the left. The move might seem counterintuitive, but investigators noted that with the design of Ju-Air Junkers, this was the correct procedure. However, the limited distance between the aircraft and the ground rendered the recovery near impossible. The crew couldn't conduct the proper procedure and the stall eventually went out of control. By that point recovery was impossible.

Conclusion

On 28 January 2021, a final report was released by the STSB which stated that "the pilots' high-risk flying was a direct cause of the accident", and that "the flight crew piloted the aircraft, at low altitude, with no possibility of an alternative flight path and at an airspeed that was dangerously low for the circumstances. The high-risk manner of flying through these not unusual turbulences caused the pilot to lose control of the aircraft. The aircraft was also being operated with its centre of gravity in excess of its rear limit". The STSB found that the aircraft was not in an airworthy condition when it took off on the accident flight, in that the engines had not been properly maintained and were not producing rated power. The report indicated that the company had a poor safety culture that tolerated risky behaviour and rule breaking.