B2/2010L Ultralight aircraft accident at Jämijärvi on 30 June 2010

An aircraft accident took place in the vicinity of Jämijärvi airfield on Wednesday 30 June 2010 at 13.05. An EV-97 Eurostar ultralight aircraft on a cross-country flight crashed to the ground soon after take-off and was totally destroyed. Both the pilot of the aircraft and the passenger were killed.

The purpose of the flight was to pick up a passenger from Jämijärvi airfield and after that fly to Tampere-Pirkkala aerodrome. Soon after take-off the canopy of the aircraft opened and among others, documents and the pilot’s and aircraft’s briefcases fell from the aircraft. After the canopy opened the aircraft flew at about 120 metres altitude loosing airspeed. After a short phase of level flight the altitude diminished quickly to about 50 metres. Before hitting the ground the altitude increased a little, at the same time the airspeed diminished and the aircraft heading changed strongly to the left. The aircraft hit the ground less than a minute after the take-off in a nearly horizontal position a little over a kilometre to the west of the airfield.

The opening of the canopy was likely due to a strong and gusty wind and the locking mechanism of the canopy. The aerodynamic forces created by gusts cause momentary changes in the aircraft’s structures, under these kind of circumstances, according to the manufacturer, the original locking mechanism is not sufficient. The manufacturer has tried to improve the reliability of the locking system by publishing a bulletin giving instructions to change the new parts to the locking system which prevent opening of the locking during momentary structural changes. Parts had been changed into the canopy locking mechanism of the aircraft, but one part considerably contributing to the reliability of locking had not been changed. The factor most contributing to this was that the instructions in the published bulletin for assembling the delivered alteration parts were inadequate. Another reason for not changing the part was the aircraft owners’ understanding that the changed parts increased the reliability of the locking the way they expected.

The reason of the accident was loss of aircraft control after the canopy opened during flight. An open canopy causes with its airflow disturbances a strong vibration to the horizontal stabilizer and elevator as well as stick and a considerable nose down effect to flight characteristics. Also the fact that the pilot probably tried to close the canopy contributed to the loss of control of the aircraft as monitoring the flight parameters was neglected.

The aircraft canopy likely opened due to momentary changes to canopy structure caused by aerodynamic forces of the strong gusty wind. To prevent this kind of unintentional opening of the canopy the manufacturer has improved the canopy locking mechanism by new alteration parts. All new parts had not been assembled into the accident aircraft.

The investigation commission gave two safety recommendations to the manufacturer Evektor-Aerotechnik a.s. It was recommended that the manufacturer publishes in the EV-97 aircraft pilot’s operating handbook procedures for the event that the canopy opens during flight. Secondly, it was recommended to the manufacturer that it publishes an instruction bulletin to correspond with the alteration work.

B2/2010L Report (pdf, 0.61 Mt)