WPR10LA147

During takeoff roll, with the airplane between 60 to 70 knots, the inner tube in the nose gear tire failed, causing the tire to flatten and skid and the nose gear to subsequently collapse. The pilot successfully aborted the takeoff and steered the airplane to a stop onto grass just off the right side of the runway. A postaccident examination of the airplane's nose landing gear retract mechanism revealed that the bolt which connects the mechanism's inboard and outboard arms in place had failed in overstress, likely due to the skidding nose gear tire. The failure of the bolt allowed both arms to pivot enough to keep the nose gear retract brace assembly from locking the nose gear in the extended position, which allowed the nose landing gear to collapse.

On February 9, 2010, about 1202 Pacific standard time, a Beech 58P, N3700N, sustained substantial damage following a nose landing gear collapse during takeoff roll at the Portland International Airport (PDX), Portland, Oregon. The certificated private pilot and his sole passenger were not injured. Visual meteorological conditions prevailed at the time of the accident, and an instrument flight rules (IFR) flight plan was filed. The personal cross-country flight was being operated in accordance with 14 Code of Federal Regulations Part 91. The flight was originating at the time of the accident, with the destination reported as the Friedman Memorial Airport (SUN), Hailey, Idaho. In a written statement provided to the Safety Board investigator-in-charge (IIC), the pilot reported that during the takeoff roll at about 60 to 70 knots [indicated airspeed], the inner tube in the nose gear failed, which caused the tire to "flatten and skid." The pilot stated that he aborted the takeoff by closing the throttle, and that the "skid" caused the nose wheel downlock to fail, allowing the nose gear to retract. The pilot added that he used main wheel braking to steer the aircraft to a stop on the grass off the right side of the runway. According to a Federal Aviation Administration (FAA) airworthiness inspector who conducted a post accident examination of the airplane, damage was observed to the airplane's most forward bulkhead area and surrounding structure, specifically the left and right keels, which had been ground down by more than one-half inch. It was also revealed during the examination that bolt (part number 130909B20), which connects the inboard and outboard arms of the nose landing gear retract mechanism, had failed. According to a Hawker Beechcraft air safety investigator, when the bolt head separated from the bolt shaft it allowed the inboard arm (p/n 002-820016-29) and the outboard arm (p/n 002-820016-27) to pivot enough to keep the nose gear retract brace assembly from locking the nose gear in the extended position, thus allowing the nose gear to collapse. The IIC submitted the nose landing gear retract mechanism's failed bolt and the inboard arm to the NTSB Materials Laboratory in Washington, D.C. for further examination. The NTSB metallurgist reported that a visual inspection of the mating fracture surfaces of the bolt indicated that the bolt fractured in the grip region about 0.1 inch from the head in a downward shear due to overstress. The metallurgist also reported that the markings on the head of the accident bolt do not meet the marking requirements of AN3. (Refer to NTSB Materials Laboratory Report No. 10-057F, which is in the public docket.) A review of aircraft maintenance records revealed that during the airplane's most recent annual inspection, which was conducted on November 20, 2009, the following entry was made: "...Rigged nose gear retract rod for proper down lock tension."