IAD99LA064

The pilot flew in VFR conditions and completed a visual approach to Runway 06. The pilot stated the landing was 'a little bumpier than some, but not a hard landing' and that the airplane 'ballooned' before its final touchdown. After the final touchdown, the right main landing gear collapsed and the airplane veered off the side of the runway. Examination of the landing gear revealed a fracture in the web area of the trunnion. An Airworthiness Directive and a service bulletin from the manufacturer called for inspection of the web area for cracks, 'To prevent collapse of the main landing gear caused by cracked trunnions, which could result in airplane damage.' Detailed metallurgical examination of the landing gear revealed that the fractures were due to overstress and that no pre-existing fractures were observed.

On September 2, 1999, at 1754 eastern daylight time, a Piper PA-34-220T, N6915Z, was substantially damaged during landing at the Nantucket Municipal Airport (ACK), Nantucket, Massachusetts. The certificated private pilot and passenger were not injured. Visual meteorological conditions prevailed for the personal flight that originated at Baltimore, Maryland, approximately 1539. An instrument flight rules (IFR) flight plan was filed for the flight conducted under 14 CFR Part 91.

In a telephone interview, the pilot reported the purpose of the flight was to visit his home in Nantucket. He said he flew IFR in visual conditions and completed the visual approach to Runway 06 at ACK. The pilot said:

"I flew a normal approach by VASI at 90 knots. As we came down, the landing was a little bumpier than some, but not a hard landing. We touched down in the first 25 percent of the runway. During rollout, the right main gear wouldn't support the airplane and we veered right and stopped."

In a written statement, the pilot said:

"Upon landing, [the] airplane ballooned slightly and upon final contact with the runway, the airplane dipped to the right and skidded to a stop."

A Federal Aviation Administration (FAA) Aviation Safety inspector examined the airplane at the scene. He said the airplane sustained damage to the right main gear and both propellers. The inspector said the nose gear collapsed and the nose gear support structure was damaged. He said:

"The right main landing gear trunnion cracked in the web area as referenced in Airworthiness Directive 94-13-11 and Piper Service Bulletin 787B. However, this airplane is outside the affected serial numbers in the AD. The AD pertains to serial numbers 34-8133001 through 34-8233088. The accident airplane is serial number 34-8533003."

According to the inspector, the last annual inspection of the airplane was completed June 3, 1999. The mechanic cited the AD, but noted non-compliance due to the serial number of the airplane.

The pilot reported 6,500 hours of flight experience, 75 hours of which were in the 90 days prior to the accident. The pilot reported 50 hours of experience in make and model.

Weather reported at ACK at the time of the accident was clear skies with winds from 090 degrees at 7 knots.

A review of Airworthiness Directive 94-13-11 and Piper Service Bulletin 787B revealed that compliance was: "To prevent collapse of the main landing gear caused by cracked trunnions, which could result in airplane damage..."

Both the Airworthiness Directive and the service bulletin describe the method of inspection for detection of the cracks (dye-penetrant) and the inspection intervals.

The right main landing gear was removed from the airplane and examined at the NTSB Materials Laboratory, Washington, DC. According to the Materials Laboratory Factual Report, examination of the landing gear revealed that:

"Significant bending deformation of the axle support arm was observed. This bending allowed contact between the tire and the top of the axle support arm. The wheel was also rotated around the trunnion axis relative to the front trunnion support. The rear trunnion support was bent 23 [degrees] relative to its original position.

"An examination of the fracture surface indicated that fracture occurred by overstress of the component. No evidence of fatigue or any other preexisting cracks was observed."