L2013-01 Helicopter accident on a heli-sawing flight near the city of Tampere on 10 January 2013

On Thursday 10 January 2013 the helicopter pilot was on a branch trimming flight near power line wires in the city district of Teisko in Tampere. Following a malfunction of the helicopter´s powerplant the pilot made an emergency landing on a field. The pilot suffered a minor injuries but the helicopter sustained a substantial damage. The malfunction was caused when a B-nut downstream of the Pc filter on the compressor delivery air pressure sensing line became completely unscrewed, which resulted in the loosening of the coupling and, consequently, in a loss of pressure in the engine’s power control system. The occurrence was caused by an imprecise daily inspection prior to the flight as well as non-standard practice or error in previous maintenance. Several heli-sawing accidents have occurred in Finland. In these accidents the pilots have not managed to carry out the emergency release of the heli-saw. The heavy sawing unit, assembled in a long tubular frame, poses a specific challenge to the pilot and the helicopter during emergencies.

In order to avoid similar incidents and possible accidents, the Safety Investigation Authority (SIA) recommends that

1. The helicopter manufacturer’s and the engine manufacturer’s daily instruction manuals differ as regards inspecting the paint markings of the compressor delivery air pressure sensing line’s couplings. On the basis of previous occurrences, to improve safety, the engine manufacturer decided to introduce comprehensive instructions.

Safety Investigation Authority, Finland recommends that MD Helicopters Inc review the MD 369D helicopter’s compressor delivery air pressure sensing line section in the daily inspection manual in such a manner that it complies with the engine manufacturer’s manual by including the paint markings on the B-nuts.

2. Under Airworthiness Directive EASA AD 2004–0009 R2 the control air pressure sensing lines of Rolls-Royce (Allison) 250 Series engines are critical parts as regards the safety of flight. During maintenance and reassembly it is important to provide for an independent inspection which is signed off in the maintenance documentation. It is also important to meticulously follow the Airworthiness Directive at the practical
level.

Safety Investigation Authority, Finland recommends that Transportstyrelsen and the Finnish Transport Safety Agency make certain that the maintenance organisations’ regulations require dual release processes following critical maintenance work (EC 2042/2003, Part M, subparts C & D). At the same time it must be checked that Airworthiness Directive EASA AD 2004–0009 R2 is fully implemented at the practical level as well.

3. If light single-engine helicopters flying at the height and airspeed typical to helisawing operations encounter an engine failure or some other serious fault, they will face an emergency landing rather than a controlled autorotation. Several heli-sawing accidents have occurred in Finland.

Safety Investigation Authority, Finland recommends that the Finnish Transport Safety Agency exhaustively assess the practical procedures of operators that carry out heli-sawing flights. In addition, their regulations and the content and extent of training as well as their safety margins must also be established.

4. Due to the specific features of these operations the helicopter’s sawing apparatus should be regarded as a tool, rather than external cargo.

Safety Investigation Authority, Finland recommends that the Finnish Transport Safety Agency would pay more attention during the inspections to the possible EASA approvals of the changes by sawing apparatus installations (for example equipment’s installed to the controls). Potential implications of the sawing apparatus on the maintenance program, operational restrictions, weight and balance calculations and the influences to emergency procedures should be checked. Every used sawing apparatus version should be recorded separately to the manuals.

Additional information
Air Safety Investigator
Tii-Maria Siitonen
02951 50704

L2013-01 Report (pdf, 2.47 Mt)