On March 27, 1997, an Enstrom F-28C (registration N294SB) operated by Steve Bates was involved in an aviation accident near Sacaton, AZ. Investigators recorded the probable cause as: the pilot's improper use of the collective by not maintaining rotor rpm during takeoff from a confined area. This summary draws on records from the U.S. National Transportation Safety Board (NTSB) historical archive.
During a confined area takeoff, the helicopter experienced a reduction in engine noise and rpm; after an autorotation and ground slide, the tail boom struck a tree and separated. Post-incident engine tests revealed normal operation but a dirty air cleaner.
Incident Overview
During a confined area takeoff, the helicopter passed through effective translational lift (ETL) when the pilot noticed a reduction in engine noise. Both the engine and rotor rpm needles were still joined at a position just below the bottom of the green arc.
Pilot Actions
The pilot lowered the collective and rolled the throttle full on without obtaining an increase in engine rpm. He initiated a straight-in autorotation.
Ground Slide and Damage
During the ground slide, a skid contacted a rock and the tail boom yawed. The tail boom then struck a tree and separated from the aircraft.
Post-Incident Examination
The main rotor drive belt was disconnected, and a run-up check was performed on the engine. The engine ran throughout the normal operating range, and magneto checks were within tolerances. The engine air cleaner was removed and exhibited trapped dirt and grass.