2004 Mäntsälä Colibri MB 2 accident (OH-U373)

Accident overview and investigation mandate On Tuesday, 24 August 2004, a privately built and privately owned single-seat ultralight aircraft, a Colibri MB 2, crashed near Mäntsälä, Finland. The aircraft was destroyed in the impact, and the pilot was killed. The Accident Investigation Board Finland established investigation commission B 3/2004 L, with investigator Jouko Koskimies as chair and investigator Tapani Vänttinen as member. The investigation was conducted under the purpose of accident prevention, not to assign fault or liability. ## Flight operations and weather The pilot arrived at Mäntsälä private airfield in the afternoon for a practice flight. Because the aircraft was considered difficult to control on the ground, the pilot first intended to perform take-off runs. The weather was good, with a slightly gusty wind from 270°–300° at 6–10 knots. The aircraft’s maximum allowable side-wind component was 20 km/h, about 11 knots. The pilot made four or five take-off runs on runway 22, experiencing difficulty controlling the aircraft’s heading. Between runs, the pilot stopped the aircraft with the engine running and opened the cabin hood to speak with people present. ## Final take-off and crash The final take-off occurred at about 16:25. The pilot circled on the east side of the airfield for 10–15 minutes, then flew over the field on a north-westerly heading toward Mäntsälä. The aircraft crashed at 16:43 on a rapeseed field near Metsäkulmantie 123, about three kilometres south-east of Mäntsälä centre. The accident site coordinates were 60°36.881′ N, 025°22.121′ E (WGS 84), at an elevation of about 75 metres above sea level. ## Wreckage and technical findings The aircraft struck the ground at a vertical angle of 40°–50° and banked to the right, with a crash trace heading of 044°. Propeller marks indicated that the engine had been running until impact. All outer parts of the aircraft were recovered, indicating that the aircraft had not broken apart in the air. The cabin hood frame was found separate from the cabin frame, where the hood lock lever was attached. The lock lever was open, the hinges were unbroken, and the hood-opening limiter rope was broken. The spring belonging to the lock lever was missing. The acrylic hood was shattered, with some pieces still attached to the frame. Numerous hood fragments were found along the crash trail, and some were located about 700 metres east-south-east of the accident site. These findings led to the conclusion that the hood had opened and broken in the air. The dispersion of the aircraft and the crash traces indicated a high collision speed. The aircraft was not in a spin, was not overweight, and its centre of gravity was within limits. ## Probable cause The probable cause was the accidental opening of the cabin hood lock lever during flight. The side-hinged hood opened immediately and struck the right wing, partially breaking. Based on the location of the hood fragments, the hood had opened just before the crash dive. The aerodynamic drag of the large open hood swung the nose to the right, causing the aircraft to roll rapidly to the right and enter a steep dive. The sequence occurred so quickly, and at such low altitude, that the pilot was unable to recover the aircraft. The investigation commission issued no safety recommendations.