Incident Overview
On October 16, 1990, a SA 315 B Lama helicopter, registration HB-XRD, operated by Rhein-Helikopter AG, was involved in an accident during takeoff from a landing site near Euthal, Switzerland. The helicopter had been performing logging operations earlier in the day. The flight from the base in Balzers to Euthal was conducted with a trainee pilot at the controls and the responsible pilot monitoring from the left seat, which was equipped with dual controls.
Sequence of Events
After landing at the work site, the left seat and dual controls were removed to facilitate cargo operations. During the day, the pilot conducted external load flights. In the late afternoon, to save time before darkness, the pilot decided not to reinstall the left seat and dual controls for the return flight. The mechanic and trainee pilot placed the crew's rucksacks on the cabin floor forward of the seats. With the engine running, the pilot was completing paperwork.
As the helicopter lifted off, the pilot noticed one of the rucksacks positioned dangerously close to the fuel cutoff lever. Fearing an inadvertent activation, he momentarily released the collective pitch lever and, with his left hand, jerked the rucksack away. In doing so, a strap from the rucksack caught and pulled the hydraulic system lever upward, disengaging the hydraulic servo control. The helicopter, at an altitude of 2 to 3 meters, dropped abruptly back to the ground, damaging the tail rotor and landing gear. No occupants were injured.
Findings
The investigation determined that the pilot was properly licensed and the helicopter was airworthy. Weather conditions were calm with overcast skies, visibility 5-8 km, temperature 13°C, dew point 12°C, and QNH 1016 hPa. The operator's practice of removing the left seat and dual controls to increase cargo space left the fuel cutoff, collective lever, and hydraulic lever exposed. A protective plate designed to prevent accidental activation had been removed for the dual controls and was not reinstalled, as it was left at the base.
Cause and Contributing Factors
The direct cause of the accident was the loss of hydraulic servo control near the ground due to the inadvertent closing of the hydraulic valve after the pilot released the collective pitch lever. Contributing factors included the pilot's inappropriate action and the absence of a protective device for the hydraulic lever.
Recommendation
The Swiss Federal Aircraft Accident Investigation Bureau recommended that the Federal Office of Civil Aviation verify whether the force required to hold the collective pitch lever with servo off on SA 315/316/319 helicopters equipped with LOM main rotor blades meets certification and manufacturer requirements.