N8892EPiper PA-32R-300 · 1976

On January 13, 2019, at 1746 eastern daylight time, a Piper PA-32R-300, N8892E, experienced a total loss of engine power during a visual approach to runway 5 at Lenawee County Airport (ADG), Adrian, Michigan. The airplane impacted a fence and terrain short of runway 5 and sustained substantial damage. The private pilot and an airplane mechanic received minor injuries. The airplane was registered to Northern Aviation Ltd and operated by the pilot under Title 14 Code of Federal Regulations Part 91 as a maintenance test flight. The flight was not operating on a flight plan. Day visual meteorological conditions prevailed at the time of the accident. The local flight originated from ADG at 1630.

The pilot did not complete the Narrative History of Flight section of his National Transportation Safety Board Pilot/Operator Aircraft Accident/Incident Report, Form 6120.1. The pilot provided a statement to the Federal Aviation Administration (FAA) East Michigan Flight Standards District Office (FSDO) and in that statement he stated that the flight departed with the airplane mechanic with inspection authorization (IA), who signed off the airplane last annual inspection, for a post annual inspection flight. They flew north between Jackson and Lansing, Michigan, and then proceeded southwest to Coldwater, Michigan, and then Hillsdale, Michigan. They returned for an approach and landing to ADG on runway 5 with engine power set to 14 inches of manifold pressure, landing gear extended, and flaps extended. On short final for runway 5, the "engine shutoff," and there was "no sputter - it acted as if someone shutoff the key."

Post-accident examination of the engine (Lycoming IO-540-K1G5D, serial number L-13642-48A) revealed that the crankshaft gear bolt, part number 13S19649, was fractured through. A logbook entry dated August 24, 2013, at a tachometer time of 3,399.87 hours and a time since overhaul of 0 hours, stated that the engine was disassembled, and an AN8-14 bolt was installed. The illustrated parts catalog and mandatory service bulletin 475C for the engine specified an AN8-14A bolt. The tachometer time at the time of the accident was about 3,466 hours.

Following the accident, Federal Aviation Administration inspectors from the East Michigan Flight Standards District Office interviewed the airframe and power plant mechanic (AP) that last overhauled the airplane engine. During the interview, the AP stated he is the owner of a tool and die shop that also does manufacturing of various parts for the auto industry. He spends about 25% of his working time in his hangar performing aircraft repair. He stated that he is most comfortable working on old, small, fabric covered aircraft. The AP stated that he was the one that overhauled the engine on N8892E and the IA just removed and re-installed the engine onto the airplane. The AP also stated that this was the first of the "big" Lycoming engines that he had overhauled. The AP told inspectors that he does not like using the Lycoming manuals, as they are hard to follow. The AP mentioned several times that he had contacted Lycoming to request assistance, and they worked with him in providing the necessary documentation needed for the work he was doing. The AP stated that he did not torque the crankshaft gear bolt to the engine manufacturer's specifications.

The engine overhaul was signed off by the AP.

Part 65.81 General privileges and limitations, stated:

(a) A certificated mechanic may perform or supervise the maintenance, preventive maintenance or alteration of an aircraft or appliance, or a part thereof, for which he is rated (but excluding major repairs to, and major alterations of, propellers, and any repair to, or alteration of, instruments), and may perform additional duties in accordance with §§ 65.85, 65.87, and 65.95. However, he may not supervise the maintenance, preventive maintenance, or alteration of, or approve and return to service, any aircraft or appliance, or part thereof, for which he is rated unless he has satisfactorily performed the work concerned at an earlier date. If he has not so performed that work at an earlier date, he may show his ability to do it by performing it to the satisfaction of the Administrator or under the direct supervision of a certificated and appropriately rated mechanic, or a certificated repairman, who has had previous experience in the specific operation concerned.

(b) A certificated mechanic may not exercise the privileges of his certificate and rating unless he understands the current instructions of the manufacturer, and the maintenance manuals, for the specific operation concerned.

A National Transportation Safety Board Materials Laboratory post-accident examination of the bolt revealed, that according to the dimensions for both AN8-14 and AN8-14A bolts, the grip length total length should be 1.59375 inches, the grip length should be 0.8125 inches, the threaded length should be a minimum 0.781 inches, and the diameter should be 0.500 inches in diameter. The (A) designation on the bolt part number indicates there should be no drilled hole in the shank. The fractured bolt measurements were consistent with the above dimensions and contained no drilled hole in the shank. Therefore, the bolt was consistent with an AN8-14A.

The bolt revealed that it had fractured 1.038 inches below the bolt head. Examination using visual and scanning electron microscopy (SEM) found features consistent with fatigue crack propagation and subsequent overstress. There were two smaller thumbnail cracks present on opposite 180° sides of the fracture surface. The thumbnail crack feature of the larger crack was located near the bottom of a thread root.

The smaller thumbnail crack exhibited crack arrest marks and ratchet marks, consistent with crack initiation at the thread root and propagation inward. The larger fatigue crack in the initial thumbnail area showed fatigue striations, consistent with fatigue crack propagation. This region also exhibited fatigue striations. The smaller opposite thumbnail crack also exhibited fatigue striations. In both thumbnail cracks, the striations were oriented consistent with the propagation from the outside surface inward. The small middle region exhibited dimple rupture, which had features consistent with subsequent overstress. Both fatigue cracks exhibited multiple crack initiation sites. There were no features consistent with material or mechanical defects, such as corrosion pits, pores, and voids.

The bolt features were consistent with fatigue cracking that initiated at multiple sites near the bottom of a thread root. These smaller cracked coalesced and propagated inward through more than half the crack section of the bolt. The bolt began to cycle under reverse bending, which initiated fatigue cracking at multiple sites along the thread root on the opposite side. Once both cracks had propagated inward to the extent present on the fracture surfaces, the remaining cross section of the bolt fractured from overstress.