Incident Description
The pilot reported lifting off from a road in open terrain to allow a truck to pass. The lift-off was smooth, but upon initiating forward flight, the pilot noticed shaking. As he increased the load on the rotor disk, the shaking became so violent that he could not see the ground. He then dropped the collective and reached the ground. The pilot described the sensation as "like being in the spin cycle of a washing machine when all of the weight is on one side."
Aircraft History and Damage
The helicopter had recently been imported from Canada to the United States and recertified with a US airworthiness certificate. It had previously been involved in a hard-landing accident in Japan on June 10, 1994. Damage from that accident 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 it was received in a repaired condition. However, no reference to the accident or its required repair was found in the Canadian maintenance or journey logs. There was also no record of an inspection, as outlined in the Enstrom Maintenance Manual, for main rotor blade strike or hard landing.
Metallurgical Examination
The Safety Board materials laboratory examined fragments from the steel tube pylon assembly, which consists of steel tubes welded together to form a frame structure for the helicopter. These tubes provide reinforcement for the four attachment points of the main transmission and other engine attachment points. Two of these steel tubes exhibited fatigue cracking and completely separated during operation of the helicopter.