Accident Overview
On Tuesday, 29 July 2003, at approximately 08:42 local time, a Kaman K-1200 K-MAX helicopter (registration HB-ZEH) operated by Eagle Helicopter AG was performing logging operations in the “Trute” area near Frutigen, Switzerland, about 45 km SSE of Berne. The helicopter was transporting tree trunks from the forest to a drop zone on a central landing area using a longline with a lower cargo hook. During the fifth approach of the day, while carrying two tree trunks suspended vertically, the pilot was given height information by the company flight assistant. The flight assistant warned the pilot over the radio about a fence and advised him to pull left. The two trunks impacted forcefully on the ground, gouging approximately 30 cm into the terrain and breaking in two. Subsequently, the lower cargo hook opened in an uncontrolled manner, causing the two trunk sections still suspended to fall. An assistant on the ground was struck by a tree trunk section and later died from his injuries. The pilot stated that he had not operated the cargo release.
Aircraft and Equipment
The helicopter was a single-seat Kaman K-1200 K-MAX, serial number A94-0014, powered by a Textron Lycoming T5317A-1 turbine engine. It was equipped with a belly cargo hook with a weighing system and used a Canam C60 lower cargo hook (serial number 6097) mounted on a longline approximately 50 m long. The Canam C60 was designed for loads up to 6000 lbs (2721 kg) and could be released manually or electrically via a solenoid. It featured an interlock mechanism with a hinged closure, safety catch, load beam, and a protective cage. The aircraft’s mass and center of gravity were within prescribed limits, and the helicopter itself was not damaged in the accident.
Personnel Information
The pilot, a Swiss citizen born in 1963, held a commercial helicopter pilot license issued by the Federal Office for Civil Aviation (FOCA) on 10 August 1989, valid until 4 March 2004. He had a total flying experience of 6651:45 hours, with 246:38 hours on the K-1200 type. His last medical examination on 14 July 2003 found him fit to fly. The flight assistant involved in the accident was a Swiss citizen born in 1980 with no flying experience.
Injuries and Damage
A third party on the ground was fatally injured by a falling tree trunk. The assistant who was struck was not employed by the helicopter company or the forestry company and was not wearing a safety helmet. The helicopter sustained no damage. Minor damage occurred to cultivated land.
Investigation and Probable Cause
The investigation was conducted by the Swiss Aircraft Accident Investigation Bureau (AAIB) together with the Berne cantonal police. The probable cause, as stated in the final report, is that the accident is with a very high degree of probability attributable to an uncontrolled opening of the lower cargo hook because of its defective design. The following factors were found to have contributed to the accident:
- The cargo hook certification process was not suitable for the flight operation requirements.
- The landing area was undermanned, with one flight assistant from the company.
- Organisation on the landing area was made more difficult and impossible to oversee for the flight assistant because of external helpers.
- Communication was made difficult for the external assistants because of the lack of radio equipment.
Certification Background
The Canam C60 cargo hook was certified by the manufacturer under US Federal Aviation Regulations (FAR) Part 27.865ff, which primarily focuses on the safety of the helicopter in external load operations. The hook was accepted on 29 November 2001 after passing static load, electrical, cycle, and vibration tests. However, the investigation noted that the certification process was not adapted to the operational demands encountered during flight.