Piper PA 46-350P N779MA accident near Parkersburg, West Virginia

Probable cause

The inadequate design of the engine mount by the manufacturer, resulting in collapse of the nose landing gear. Contributing to the accident was the failure of the operator to adhere to the manufacturer's suggested engine mount inspection schedule.

NTSB analysis

During landing, the airplane veered hard to the right when the nose gear was lowered to the runway after touchdown. The pilot attempted to maintain directional control with rudder input, but the airplane veered to the right and departed the runway. Initial examination of the airplane at the site revealed that the nose landing gear had collapsed and the attachment components between the nose landing gear actuator and the engine mount were fractured. Each of the right and left two-piece attachment feet were fractured at the nose landing gear actuator attach location. Detailed examination of the right foot showed evidence of fatigue, which covered a 0.75-inch arc and approximately 0.04 inches of the 0.06-inch wall thickness of the foot. The left foot also showed evidence of fatigue, which covered a 0.35-inch arc and was approximately 0.03 inches deep.

The manufacturer had issued a series of Service Bulletins (SB 1103, with subsequent revisions A, B, and C) for PA-46-350P models that required inspections for cracks in the engine mounts in the areas of the nose landing gear actuator attachment feet. Inspections were to take place at the next regularly scheduled maintenance event, and at each 100 hours time in service or annual inspection, whichever occurred first. Records showed that SB 1103B was accomplished on the accident airplane during an annual inspection in 2007, but records of subsequent annual inspections in 2008 and 2009 showed that SB1103 was not accomplished. Previous nose gear failures and runway excursions resulted in the redesign of the original engine mount due to compliance (flexibility) in the engine mount actuator attach feet structure. 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 Federal Aviation Administration did not mandate the actions outlined in SB 1103B, but compliance could have alerted the operator of any problems because the SB inspection criteria called for examinations of the engine mount in the areas where the fatigue cracks were located. Replacement of the engine mount with the new design that had one-piece nose landing gear actuator attachment feet would have relieved the operator of the manufacturer's repetitive inspection requirement, but because the accident airplane still had the welded two-piece attachment feet it was subject to the repetitive inspection per the service bulletin.

Text from the NTSB. Open the NTSB docket for ERA10LA237 for the full record.