Piper PA44 N2163F accident near Miami, Florida

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.

NTSB analysis

The flight instructor reported that the student pilot's approach and landing during the instructional flight were normal. During the landing roll, the nose landing gear (NLG) collapsed, which resulted in structural damage to the airframe.

Examination of the NLG revealed that an upper drag link and associated knee bolt were broken. Subsequent examination of the upper drag link revealed that it had failed due to overstress; however, the knee bolt had failed due to reverse-bending fatigue from relatively high-cyclic stresses. Given the failure location, it is likely that excessive wear in the bearing preceded the bolt failure.

The airplane manufacturer had issued a service bulletin applicable to the accident airplane, which recommended the inspection of the NLG drag link assembly and replacement of the associated knee bolt at 500-hour intervals. Further, the Federal Aviation Administration subsequently issued a special airworthiness bulletin, which recommended that the NLG drag link assembly inspection and knee bolt replacement interval be reduced to 400 hours time in service (TIS) for airplanes that experienced greater-than-normal landing cycles per flight hour, including airplanes used for flight school operations like the accident airplane. A review of the airplane's maintenance records revealed that the failed knee bolt was replaced about 386 hours TIS before the accident. Although the records indicated that the flight school followed the 500-hour interval not the 400-hour interval, the bolt had been replaced at less hours TIS than the recommended interval; therefore, the reason for the premature excessive wear could not be determined.

Text from the NTSB. Open the NTSB docket for ERA15LA225 for the full record.