Incident Overview
A helicopter was operating a series of 5-minute for-hire sightseeing flights for airshow patrons. During one flight, the pilot transmitted over the local control frequency that he had experienced a power failure and was going down.
Witness Observations
Another helicopter pilot witnessed the incident aircraft at an estimated altitude of 300 feet above ground. The witness described the helicopter as being in a nose-high attitude, yawing to the right, and descending vertically. The yawing motion continued throughout the descent, and just before ground impact, the helicopter was slightly nose-low.
Post-Accident Examination
Responding fire department personnel did not find any fuel leaks in the tanks or fuel lines. FAA inspectors subsequently examined the fuel system and confirmed it was intact, with no evidence of tank or line rupture. During recovery, approximately one pint of fuel was drained from each of the helicopter's fuel tanks.
Fuel Management System
The operator stated that a computed tabulation system was used to track the fuel onboard the helicopter. This system involved subtracting estimated fuel usage from the amount believed to be onboard and adding fuel added during the day. No calibrated dipstick was used to verify the actual fuel quantity in the tanks.
Component Examination
All three main rotor blades were found coned upward. The tail rotor blades were undamaged. The engine was removed and placed in a production test cell, where it ran normally, indicating no mechanical failure.
Fuel Gauge Testing
The fuel gauge was tested and found to read accurately at zero (indicating empty). However, as fuel was added, progressively higher errors were noted. At one-quarter of the system's capacity, the gauge displayed twice the actual amount of fuel.