NTSB Identification: SEA08FA071
Nonscheduled 14 CFR Part 135: Air Taxi & Commuter
Accident occurred Thursday, February 07, 2008 in Hilo, HI
Probable Cause Approval Date: 01/29/2009
Aircraft: MCDONNELL DOUGLAS 369E, registration: N698DM
Injuries: 5 Minor.
The flight was approximately five miles from the departure airport when the pilot turned back
due to a fuel bypass caution light. The pilot heard 2-3 abnormal engine sounds, with
simultaneous yawing, during the turn and entered an autorotation. During the final stages of
the autorotation, the engine flamed out. The helicopter touched down on uneven terrain and
rolled over resulting in substantial damage. Post accident examination of the engine assembly
revealed a fuel leak from the fuel filter pressure differential switch. The differential switch
was in place and the associated fuel lines, bushing and adapter fitting were not damaged.
Examination of the system revealed that one of the three fuel filter pressure differential
switch set screws, and associated safety wire segment, was missing. The two remaining
screws were in place. One of the screws was fixed, the other finger tight. The corresponding
safety wire was attached to the remaining set screws. The distal end of the safety wire leading
to the missing set screw was severed. A post accident evaluation of the engine in a production
test cell revealed a fuel leak at the pressure differential switch when the engine was motored
to 16 percent N1 (compressor speed). The original fuel filter pressure differential switch was
removed and replaced with an exemplar differential switch. A second engine start was
successful and the engine ran, without leaks, and attained normal operating parameters.
Maintenance records indicated that the helicopter's fuel system components were inspected
during the 100-hour inspection completed 66 flight hours before the accident. The
maintenance "check sheet" indicated that the engine's fuel system components, to include fuel
lines and connections, were inspected for leaks or damage, and no anomalies were noted. No
record was found in the maintenance records of any work done to the fuel filter pressure
differential switch subsequent to the 100-hour inspection. It could not be determined when, or
how, the fuel filter pressure differential switch set screws, and associated safety wire came
loose. The approved maintenance manual for the helicopter contains multiple warnings
indicating that air in the closed fuel system will cause a power reduction or flame out.
The National Transportation Safety Board determines the probable cause(s) of this accident
as follows:
A leak in the fuel filter pressure differential switch that resulted in a loss of engine power.
Contributing to the accident was uneven terrain that hindered a successful emergency landing