The summary below is taken from page IX of the report.
AIRCRAFT ACCIDENT RESULTING IN THE DEATH OF EIGHT SKYDIVERS AT
JÄMIJÄRVI ON 20 APRIL 2014
On Easter Sunday, 20 April 2014 at 15:40 Finnish time (UTC + 3h) an accident occurred at Jämijärvi aerodrome when a Comp Air 8 aircraft, registration OH-XDZ, carrying skydivers crashed into the woods. In addition to the pilot there were ten skydivers on board. The pilot and two skydivers managed to bail out of the aircraft. Eight skydivers died in the collision with the ground.
The OH-XDZ was the first turboprop aircraft in the experimental category in Finland. It was built in Finland from an aircraft kit.
The Tampere Skydiving Club’s (TamLK) skydiving event “Easter Boogie” was in progress at Jämijärvi aerodrome. Finland’s Sport Aviators’ Comp Air 8 aircraft was reserved for the event; with it skydivers were being carried to the altitude of 4 000 m.
The eighth Comp Air flight of the day reached the jump run, which was at 4 230 m over the southern runway of the aerodrome. The skydivers noticed that they had overshot the jump run and requested a new one from the pilot. The pilot increased engine power and simultaneously began turning to the left. During the turn the aircraft began to descend and its airspeed increased, which the pilot did not immediately realise. The pilot pulled on the control stick and the aircraft levelled out or went into a shallow climb. He reduced engine power to idle, in conjunction with which the airflow over the horizontal stabiliser probably decreased suddenly, which generated a rapid nose down movement. As the angle of attack was decreasing a downward force was generated on the wing. The right wing’s wing strut buckled upwards and the right wing folded down against the jump door around the wing root mountings. The aircraft lost its controllability instantaneously and began to rotate around its vertical axis in a flight condition resembling an inverted spin.
In the aircraft a decision to make an emergency jump was made. The wing which had folded against the jump door prevented exiting through the door. The pilot and two skydivers sitting at the front of the airplane bailed out through the pilot’s door. The others did not have enough time to bail out. They died in the collision with the ground. The aircraft was completely destroyed in the collision and the fire.
There were several eyewitnesses to the accident and the emergency call was made immediately. The first third parties reached the accident site within six minutes. Skydivers on the ground immediately started a search to locate the ones that had bailed out of the aircraft. The first rescue unit reached the site 13 minutes after the accident. The number of survivors remained uncertain for a long time. The last victim was found inside the wreckage four hours after the accident.
The investigation revealed that it was likely that the centre of gravity of the aircraft was outside the flight manual’s aft limit on the jump run. The rating requirements for pilots in skydiving operations are incompatible with the demands of the activity.
When the material of the right wing strut was analysed it became clear that there was a fatigue crack on the inner surface of the wing strut. The crack had formed over a long period of time and it was impossible to detect in visual inspections. No other pre-existing technical fault was found in the investigation of the wreckage.
A winglet structure was installed on both wings of the aircraft; the design comprised a wing extension at the plane of the wing and a winglet. The Permit to build-application did not mention these, nor had their effects on the aircraft’s structural strength or flight characteristics been established prior to commencing the construction. According to the results of an analysis commissioned for the investigation the wing modifications increased the aerodynamic loads on the aircraft. The kit manufacturer had presented the load calculations of the original aircraft, but they were not given to the builders.
According to calculations the safety factor for the wing strut’s actual stress resistance, given in the Permit to build, did not materialise at -1.8 g at the maximum weight. The minimum requirement as per Aviation Regulations was met.
Coordination and communication between the authorities that participated in the rescue operation did not succeed on all fronts; however, this had no bearing on the onset or extent of the damage. The need for psychosocial support was great. Later there were shortcomings in the arrangements for psychosocial support.
The cause of the accident was that the stress resistance of the right wing’s wing strut was exceeded as a result of the force which was generated by a negative g-force. The force which resulted in the buckling of the wing strut was the direct result of a negative (nose-down) change in pitching moment, in conjunction with an engine power reduction intended to decrease the high airspeed.
The contributing factors were the following:
- There was a fatigue crack on the wing strut. Because of the damage to the aircraft it was not possible to investigate the mechanism of the fatigue crack formation. It is possible that, in addition to the stress caused to the aircraft by short flights and high takeoff weights, the temperature changes caused by the jet blast as well as vibration contributed to the fatigue cracking.
- The nature of skydiving operations generated many takeoffs and landings in relation to flight hours. A significant part of the operations was flown close to the maximum takeoff weight. These factors increased the structural stress.
- The pilot’s limited flight experience on a powerful turboprop aircraft, his inadequate training as regards aircraft loading and its effects on the centre of gravity and airplane behaviour, the high weight of the aircraft and the aft position of the CG in the beginning of a new jump line and, possibly, the pilot’s incorrect observation of the actual visual horizon contributed to the onset of the occurrence.
During the turn to a new jump run the aircraft began to descend and very rapidly accelerated close to its maximum permissible airspeed. The pilot did not immediately realise this.
- The structural modifications on the wing increased the loads on the aircraft and the wing struts. Their effects had not been established beforehand. The kit manufacturer was aware of the modifications. No changes to the Permit to build were applied for in writing regarding the modifications. Neither the build supervisor nor the aircraft inspectors were aware of the origin or the effects of the modifications.
As a result of the investigation the Safety Investigation Authority, Finland issued five recommendations; three to the Finnish Transport Safety Authority, one to the European Aviation Safety Agency and one to the Ministry of Social Affairs and Health.
The Finnish Transport Safety Authority should:
- Limit the number of occupants in experimental aircraft and their use in skydiving operations based on risk considerations.
- Ensure that the experience and training of persons that supervise and inspect experimental aircraft construction meet the requirements of construction and modification control, and
- In conjunction with the recreational aviation safety project, ensure that the Finnish Aeronautical Association prepares generic guidelines for skydiving operations, around which associations build a training programme and proficiency checks for jump pilots.
The SIAF recommends that the European Aviation Safety Agency prepare specified theoretical knowledge and flight training requirements for pilots-in-command in skydiving operations.
The SIAF repeats the recommendation to the Ministry of Social Affairs and Health which was originally issued by the Investigation Commission of the Kauhajoki School Shooting in 2008. The Ministry should take steps to ensure that the plans, resources, responsibilities, and competent leadership for the provision of psychosocial support in major crises are available regardless of where the accident takes place or where the people involved come from.