NTSB Identification: DEN07LA030.
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Accident occurred Thursday, November 30, 2006 in Steamboat Sprng, CO
Probable Cause Approval Date: 07/25/2007
Aircraft: Piper PA-46-500TP, registration: N804JH
Injuries: 1 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
During takeoff, the pilot applied power to the engine and the takeoff roll was smooth. The pilot noted that the runway centerline was somewhat obscured by snow and the airplane drifted slightly to the right of centerline. Approximately 50 to 60 knots (1/3 of the way down the runway), the airplane "suddenly turned hard to the left and started to skid." The pilot immediately reduced power to idle and did not apply brakes or reverse. Subsequently, the airplane departed the left side of the runway. After repairs were completed from a previous incident, the accident airplane was equipped with a Supplemental Type Certificate (STC) engine mount that eliminated the need for repetitive inspections required by the airframe manufacturer service bulletins. Due to the number of runway excursions, nose gear failures and recurring cracked engine mounts, the original engine mount was redesigned. The redesign process included finite element model analysis and various testing programs. The original mount design had not incorporated these types of design tools. Post-event engineering examination of the original engine mount and STC'd engine mount revealed that there was compliance (flexibility) in the engine mount actuator attach feet structure, sometimes resulting in the cracking of the engine mount at the actuator feet. This compliance issue was sometimes exasperated at various speeds, resulting in a high speed shimmy effect and subsequent uncommanded left or right turn of the nose wheel during takeoff and/or landing. The new engine mount incorporates a one piece design at the actuator attach point, eliminating the two piece feet design. The one piece design provides a less compliant structure, which prevents relative motion between the two feet in the original engine mount design.
The National Transportation Safety Board determines the probable cause(s) of this accident to be: The inadequate design of the engine mount which caused an uncommanded left turn, loss of directional control, and impact with snow covered terrain. Full narrative available
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