NTSB Factual Report

On May 23, 2015, about 1605 eastern daylight time (EDT), a Piper PA-44-180, N2163F, was substantially damaged after the nose landing gear collapsed while landing at Miami Executive Airport (TMB), Miami, Florida. The private pilot-rated student, an air transport-rated flight instructor, and one passenger were not injured. The airplane was operated by Pilot Training Center LLC under the provisions of Title 14 Code of Federal Regulations Part 91 as an instructional flight. Day, visual meteorological conditions prevailed, and no flight plan was filed. The flight originated at West Palm Beach, Florida (OBE) at 1530.

The flight instructor reported that his student performed a normal approach and landing to runway 9R at TMB. During the landing roll, the nose gear collapsed. The airplane came to a stop on the runway and the occupants exited the airplane.

A Federal aviation Administration (FAA) inspector responded to the accident site and examined the airplane. The nose gear was collapsed into the wheel well, and the main gear remained extended. The nose gear upper drag link and associated knee bolt were broken. The pitot tube on the left wing was pushed up into the wing structure, resulting in structural damage. Both propellers struck the runway and all blades were damaged.

The nose landing gear upper drag link and knee bolt were removed and forwarded to the NTSB Materials Laboratory for examination and analysis.

The examination of the upper drag link revealed matte gray and rough fracture surfaces consistent with overstress. The associated knee bolt bushing was cracked and deformed on both sides.

The examination revealed that the knee bolt was fractured near the middle of the grip section. The surface of the shank was dark gray in color and showed no evidence of circumferential scoring damage. The head of the bolt was marked "NAS 6204-270 CS." The fracture surface of the knee bolt was examined under magnification. Portions of the fracture surface had a lighter gray color with curving crack arrest lines, consistent with fatigue. The fatigue regions emanated from origins on opposite sides of the bolt, a feature consistent with reverse bending fatigue. The fatigue region showed ratchet marks and relatively rough texture, features consistent with fatigue crack initiation and growth under relatively high cyclic stress.

Piper Service Bulletin (SB) 1156, issued April 7, 2005, required periodic replacement of the nose gear drag link knee bolt on certain Piper aircraft, including the PA-44-180. The SB was issued in response to circumferential score marks that could develop in the bolt over time, causing stress concentrations to develop that could eventually lead to failure of the bolt. The SB called for inspections of the bushings in the knee joint for the upper and lower drag links for serviceability and for the knee bolt to be replaced at 500-hour intervals.

Although SB 1156 called for a National Aerospace Standard (NAS) 464P4 bolt, the bolt installed in the accident airplane was a NAS6204 bolt. The NAS6204 bolt met the size and harness requirements of the SB. Since issuance of the SB, the NAS464 bolt was discontinued for new designs and replaced with the NAS6203 through 6220 bolts.

On May 4, 2010, the FAA issued Special Airworthiness Information Bulletin (SAIB) CE-10-30 in response to another Piper PA-44-180 airplane that experienced a nose gear collapse during landing due to a fractured nose gear drag link knee bolt. Additionally, it was noted the airplane from SAIB CE-10-30 was used in flight school operations where higher than normal landing cycles were common. In SAIB CE-10-30, the FAA recommended that for airplanes that experience greater than normal landing cycles per flight hour, the inspections of the nose gear drag link assembly and knee bolt replacement per Piper SB 1156 should be reduced to 400 hours time in service (TIS).

According to maintenance records for the accident airplane, the nose gear assembly was replaced as noted in an entry dated May 15, 2014. According to correspondence with maintenance personnel for the airplane, the nose assembly was replaced due to a collapse of the nose gear where the knee bolt was broken. According to the May 15, 2014, log book entry, the repair incorporated Piper SB 1156 and also noted that SB 1156 was to be repeated every 500 hours TIS. At the time of the last log book entry on May 20, 2015, which was a 100-hour inspection, the airplane had accrued 386.2 hours TIS since the May 15, 2014 entry. According to FAA records, the accident airplane has been registered to Pilot Training Center, LLC, since April 25, 2012. No reference to FAA CE-10-30 or any reduced interval for inspection and knee bolt replacement on airplanes used in flight training operations was noted in the log book entry on May 15, 2014.

NTSB Probable Cause

The failure of the nose landing gear upper drag link knee bolt due to reverse-bending fatigue, which was likely preceded by excessive bearing wear due to reasons that could not be determined based on the available evidence.