Incident Overview
On May 23, 2015, at approximately 1605 eastern daylight time, a Piper PA-44-180, registration N2163F, sustained substantial damage when its nose landing gear collapsed during landing at Miami Executive Airport (TMB) in Miami, Florida. The airplane was operated by Pilot Training Center LLC under 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 from West Palm Beach, Florida (OBE) at 1530.
The flight instructor reported that his student performed a normal approach and landing to runway 9R. During the landing roll, the nose gear collapsed. The airplane came to a stop on the runway, and the three occupants (private pilot-rated student, air transport-rated flight instructor, and one passenger) exited uninjured.
Damage and Examination
A Federal Aviation Administration (FAA) inspector examined the airplane. The nose gear had collapsed into the wheel well, while the main gear remained extended. The nose gear upper drag link and its associated knee bolt were broken. The left wing pitot tube was pushed upward into the wing structure, causing structural damage. Both propellers struck the runway, damaging all blades.
The upper drag link and knee bolt were sent to the NTSB Materials Laboratory for analysis. The upper drag link fracture surfaces were matte gray and rough, consistent with overstress. The knee bolt bushing was cracked and deformed. The knee bolt itself was fractured near the middle of its grip section. The shank surface was dark gray with no circumferential scoring. The bolt head was marked "NAS 6204-270 CS." Under magnification, parts of the fracture surface showed lighter gray with curved crack arrest lines, indicating fatigue. Fatigue origins were on opposite sides of the bolt, consistent with reverse bending fatigue. Ratchet marks and rough texture suggested fatigue crack initiation and growth under relatively high cyclic stress.
Maintenance History and Service Bulletins
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 addressed circumferential score marks that could cause stress concentrations and eventual bolt failure. It called for inspections of the knee joint bushings and replacement of the knee bolt at 500-hour intervals.
Although SB 1156 specified a National Aerospace Standard (NAS) 464P4 bolt, the accident airplane had an NAS6204 bolt installed. The NAS6204 met size and hardness requirements, and the NAS464 bolt had been discontinued and replaced by the NAS6203-6220 series.
On May 4, 2010, the FAA issued Special Airworthiness Information Bulletin (SAIB) CE-10-30 after another PA-44-180 nose gear collapse due to a fractured knee bolt. That airplane was used in flight school operations with higher-than-normal landing cycles. SAIB CE-10-30 recommended reducing the knee bolt replacement interval to 400 hours time in service (TIS) for airplanes experiencing greater than normal landings per flight hour.
Maintenance records for the accident airplane showed that the nose gear assembly was replaced on May 15, 2014, due to a previous nose gear collapse where the knee bolt had broken. The logbook entry for that replacement incorporated Piper SB 1156 and noted the 500-hour TIS repeat interval. At the last logbook entry on May 20, 2015 (a 100-hour inspection), the airplane had accumulated 386.2 hours TIS since the May 15, 2014 entry. No reference to FAA SAIB CE-10-30 or any reduced inspection interval was noted in the logbook.
The accident airplane had been registered to Pilot Training Center, LLC since April 25, 2012.