NTSB Identification: SEA98FA055.
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Accident occurred Monday, March 30, 1998 in BAKER, OR
Probable Cause Approval Date: 01/10/2000
Aircraft: Enstrom F28F, registration: N171HH
Injuries: 1 Uninjured.

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.

The pilot stated that he had lifted off from a road in open terrain so that a truck could get by. He stated that the lift-off was smooth. He noticed some shaking when he began forward flight. He increased the load on the rotor disk and the shaking became so violent that he couldn't see the ground. He dropped the collective and reached the ground. He said that the only way he could describe the situations was that 'it was like being in the spin cycle of a washing machine when all of the weight is on one side.' The helicopter had recently been imported to the US from Canada, and recertified with a US airworthiness certificate. The helicopter had been involved in a hard-landing accident in Japan on June 10, 1994. Damage to the aircraft at that time included the left skid, deformation of the fuselage and twisting of the tail boom. All three main-rotor blades had terrain impact The helicopter was later exported from Japan to Canada, where the importee stated that it was received in a repaired condition. No reference to the accident or its required repair was made in the Canadian maintenance or journey logs. No record was found for accomplishment of an inspection, as outlined in the Enstrom Maintenance Manual, for main rotor blade strike or hard landing inspections. The Safety Board materials laboratory inspected fragments from the steel tube pylon assembly, consisting of pieces of steel tubing that are welded to each other to form a frame structure for the helicopter. The steel tubes provide reinforcement for the four attachment points of the main transmission and other attachment points for the engine. Two of the steel tubes exhibited fatigue cracking, and completely separated during operation of the helicopter.

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

Fatigue failure of the steel tubing pylon structure. Factors include inadequate inspection by maintenance personnel of damage after a previous accident.

Full narrative available

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