What happened
On May 23, 1997, an Enstrom 280C helicopter, registration HB-XMO, was conducting private pilot training at Buttwil airfield. The flight, operated by Flugschule Eichenberger AG, involved an instructor and a student performing various maneuvers, including simulated tail rotor failures and autorotations.
After completing several exercises, the instructor instructed the student to perform a circuit. Upon takeoff, the student rotated the aircraft 90 degrees to the right to monitor the approach area. During this phase, a critical discrepancy arose between the crew's accounts regarding verbal instructions. The student claimed the instructor commanded "left foot," while the instructor maintained he was attempting to correct an over-rotation by calling for "right foot." This led to a rapid, uncontrolled rotation around the vertical axis. The aircraft struck the ground while spinning, resulting in the destruction of the helicopter and two crew members being injured, with the student sustaining severe injuries.
The investigation
SUST examined the cockpit configuration and the actions of both pilots. The investigation confirmed that both pilots held valid licenses and were in good health. No mechanical failures or technical defects were found in the Enstrom 280C following the inspection.
Investigators noted that while the dual controls were functional, the horizontal footrests on the instructor's side pedals had been removed and were stored in the luggage compartment. The instructor admitted to removing these rests frequently to avoid interference with his movements. The investigation also reviewed the conflicting testimonies regarding the specific verbal command issued during the rotation.
Findings
- The primary cause of the accident was the improper use of the tail rotor controls.
- A significant misunderstanding occurred between the instructor and the student regarding a verbal command.
- The instructor's ability to intervene may have been compromised because the tail rotor pedals were only partially installed, lacking the necessary footrests.