C3/2003L Damage on landing of Agusta Bell 412 helicopter in Pirttisaari on 31 March 2003

On Monday 31 March 2003 at 13.25 Finnish time there was a helicopter incident at Pirttisaari, about 25 km south-west of Helsinki. A Finnish Frontier Guard Agusta Bell 412 helicopter OH-HVE was damaged on a training flight during landing when its main rotor blades hit a lamp post. There were five crew members on board, but no one was injured. The helicopter was severely damaged. The Accident Investigation Board Finland decided to investigate the incident and appointed Jouko Koskimies investigator-in-charge and Kalevi Nordman a member investigator.

The flight was a half-hour training flight as a part of the Frontier Guard flight mechanic training program. The purpose of the flight was to train the mechanic to give manoeuvring instructions to the pilot when landing on the terrain. Take-off from Malmi airport was at 12.55. The flight consisted of five approaches, of which the last was made onto the floating concrete jetty of the Pirttisaari Coast Guard station. The surface wind was 340° and 8-10 knots. The crew had not landed this jetty. The place met the requirements for a landing area. Restricting obstacles were bollards and approximately 4,2 m high lamp post in the middle of the jetty. The pilot-in-command flew the helicopter. Student mechanic was standing backwards on the right skid and gave the manoeuvring instructions. Instructor mechanic on the middle backseat supervised him. The original intention was to land to the east end of the jetty but since there was a loose rope bundle, the place was changed to the west end of the jetty. While approaching the jetty the helicopter was instructed to the left side of the lamp post at a height of about half a meter. Then the left landing skid came over the bollards. Student mechanic estimated the distance of 1-2 m between the main rotor and the lamp post. He asked to move the helicopter a bit to the right away from the bollards. Moving to the left was restricted by a walking bridge. Simultaneously the pilot let the helicopter to glide forwards bringing the cabin and landing skid over the ice. The manoeuvre was agreed with the instructor mechanic. Student mechanic asked the pilot to move the helicopter backwards and warned not to move rightwards anymore because the lamp post was close. The instructor mechanic observed primarily the location of the helicopter on the jetty. The helicopter was hovering over the jetty at a height of about half a meter. When the student mechanic assumed that the helicopter was in correct position, he gave instructions for landing. When pilot let the helicopter to descend, the main rotor blades hit the lamp post. Pilot landed the helicopter immediately on the jetty because of strong vibrations. When he noticed that the helicopter settled down and the shaking diminished, he stopped the engines and main rotor and evacuated the helicopter.

The flight was carried out according to the current instructions and requirements. The weather was good and did not affect to the incident. The student mechanic paid attention to the bollards on the jetty, but did not pay enough attention to the distance to the lamp post. When the distance was estimated it was around 1-2 metres. Nevertheless, the movement of the helicopter caused the main rotor blades to be over the lamp post. This was not noticed and two rotor blades hit the lamp post and were broken apart. The support case of the main transmission box broke almost loose and both rotor drive shafts broke apart.

The cause of the incident was a mistake in estimating the distance to the lamp post. Contributing factors were lack of knowledge of the crew about the dimensions of the jetty and its obstacles, the decision to change the landing place, the unusual manoeuvring of the helicopter due to the training purposes and the fact that the instructor and student mechanic focused to manoeuvre the helicopter to the correct landing place and did not check the distance to the lamp post.

The safety recommendations were that that the Frontier Guard should amend the landing area requirements of its Flight Operations Manual by adding the required minimum distances between the rotor blades and obstacles. The mechanic flight training program and the type-specific operating procedures should be amended by instructions and standard call-outs for terrain landings. The possibilities to add more training flights to the flight training program should be studied. It is also recommended that the Frontier Guard would study the need of the crew resource management training.

The final draft of the report was sent for comments to the Flight Safety Authority and the Air Patrol Squadron of the Finnish Frontier Guard. Comments has been taken into account in the report.

C3/2003L Report (pdf, 1.09 Mt)