NTSB Identification: MIA01FA006
14 CFR Part 91: General Aviation
Accident occurred Monday, October 16, 2000 in BURLINGTON, NC
Probable Cause Approval Date: 11/28/2001
Aircraft: Aerospatiale AS-355-F2, registration: N355DU
Injuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

About 5 minutes before landing at a hospital, the main rotor gearbox (MGB) oil pressure warning light illuminated. The pilot continued to the hospital, landed, and performed an immediate engine shutdown. A mechanic disconnected the wiring to the MGB oil pressure switch and the light went out. The mechanic stated he believed the oil pressure switch had failed and he asked the pilot to run the helicopter, hover the helicopter, and if everything was normal, to fly it back to the base hospital. The pilot did the run and hover, and then departed the hospital. The helicopter crashed about 1 minute later. Witnesses stated they heard the helicopter approach the crash site at a low altitude and making a slow thumping noise. Examination of the MGB showed the oil pump idler gear had seized in the oil pump due to undetermined reasons and the oil pump drive shaft had failed due to overstress. The teeth on the engine input gears, intermediate gears, and MGB drive gear in the MGB combining gearbox had failed due to high-temperature overstress, which was the result of oil starvation. The helicopter was not equipped with a MGB oil pressure indicator. The maintenance procedure for trouble shooting an illuminated MGB oil pressure warning light is to first check the electrical circuit, and if this does not correct the problem, to change the oil pressure switch. The mechanic stated he did not have the maintenance manuals with him while working on the helicopter. The MGB had been installed in the helicopter after overhaul, 3 days and 4 flight hours before the accident.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

The mechanics failure to comply with manufacturers instructions for correction of a illuminated main rotor gearbox oil pressure warning light resulting in the helicopter being dispatched on a ferry flight with a failed main rotor gearbox oil pump, failure of the main rotor gearbox combining gearbox gears due to oil starvation, loss of main rotor RPM, and the helicopter colliding with trees and the ground during an uncontrolled descent.

Full narrative available

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