GILA BEND, AZ, USA
N991PK
Piper PA-28-150
The pilot said that no engine discrepancies were noted during either the preflight or the initial cruise portion of the flight, and that all engine instrument readings were normal. Between 500 and 1,100 mean sea level, the engine suffered a significant loss of power accompanied by sputtering, vibration, and the rpm fluctuating. He declared an emergency, performed the emergency checklist with no changes, and made a forced landing on a road. During the landing rollout the airplane struck a road sign that he had not seen. Postaccident inspection of the engine revealed the gear at the back of the crankshaft was detached and moving freely between the corresponding gears. The crankshaft gear attaching bolt and threads were undamaged and the bolt appeared to have backed out of the crankshaft and was resting in the crankshaft gear bore. The bolt locking plate remained at the head of the bolt, and exhibited fretting signatures. Fretting signatures were also located around the mating surfaces of the gear and crankshaft bore. The crankshaft gear dowel pin had failed, with fatigue striations visible to the naked eye. An engine overhaul was completed 1 month after an airworthiness directive (AD) was published requiring inspection of the crankshaft gear and the bolt to prevent the bolt from backing out and liberating the crankshaft gear. No evidence of compliance with this AD was found in the engine maintenance records.
On November 12, 1998, at 1300 hours mountain standard time, a Piper PA-28-150, N991PK, experienced a loss of engine power, made a forced landing, and struck a sign on the landing rollout on a county road at the base of Agua Caliente mountain near Gila Bend, Arizona. The airplane, rented by the pilot and operated by Plus One Flyers Inc., San Diego, California, under the provisions of 14 CFR Part 91, sustained substantial damage. The private pilot was not injured. Visual meteorological conditions existed for the personal flight that departed Montgomery Field, San Diego, at 1000 Pacific standard time. The flight was scheduled to terminate at the Sky Harbor Airport, Phoenix, Arizona. In the pilot's written statement, he reported that there were no discrepancies noted with the preflight inspection. He stated that the engine started "without difficulty," and no anomalies were encountered during the engine run-up. During cruise he noted that the engine instruments were indicating normal. In an interview with the Safety Board investigator, the pilot reported that no mechanical anomalies existed prior to the loss of engine power. He stated that all instruments were in the "green" and that the engine was running smoothly. The pilot reported that Yuma approach cancelled his flight following rather than hand him off to Albuquerque Center; which he monitored, but did not contact. He then descended to 5,500 feet to maintain compliance with VFR altitude requirements. Approximately 40 miles northwest of Gila Bend VORTAC he noted a "significant loss of engine power." The engine began to sputter and was still running, but it was not developing any power. The pilot contacted Albuquerque Center and declared an emergency. He stated that the landing was normal, but on the landing rollout he struck a road sign that he had not seen. The airplane turned 45 degrees and came to rest after sliding on gravel. The pilot reported that the engine did not stop completely, but fluctuated between 500 and 1,100 rpm. He turned on the fuel pump, switched fuel tanks, and applied carburetor heat. He stated that he did not note any further improvement with the engine and conducted the emergency checklist. The airplane was inspected at Air Transport, Phoenix, on December 9, 1998. The top spark plugs were removed, and according to Champion's Aviation Check-A-Plug Chart AV-27, were consistent with normal operation. Valve train continuity was unable to be established by rotating the propeller. The rocker box covers were removed to make sure that the rocker arms showed movement. The engine was again rotated by the propeller, but the rocker arms did not move. The accessory gear case cover was removed for examination of the accessory gears. It was noted that the gear at the back of the crankshaft was detached and moving freely between the corresponding gears. Closer inspection revealed that the crankshaft gear dowel pin had separated. The attaching bolt and threads were undamaged. The attaching bolt appeared to have backed out of the crankshaft and was resting in the crankshaft gear bore. The head of the attaching bolt did exhibit a mark that was attributed to the bending of the locking plate. The bolt locking plate remained at the head of the bolt, and exhibited fretting signatures. It was also noted that there were fretting signatures located around the mating surfaces of the gear and crankshaft. A Safety Board investigator inspected the crankshaft gear dowel pin under a microscope and noted that it exhibited beach marks. Airworthiness Directive (AD) 91-14-22 became effective on August 19, 1991, and referenced Textron Lycoming Service Bulletin 475A. The text of the AD noted that issuance was "to prevent loosening or failure of the crankshaft gear retaining bolt, which may cause sudden engine failure . . ." The AD and the referenced Textron Lycoming SB 475A required an inspection and rework of the crankshaft bore and gear interface, and the gear retaining bolt hole threads. Compliance with the AD was stated as during each engine overhaul, after a propeller strike, sudden stoppage, or whenever gear train repair is required. Review of the engine logbook revealed that a major engine overhaul was competed on September 2, 1991. The original work order was unavailable to Safety Board investigators to determine if work related to the AD compliance was accomplished during the overhaul. An undated entry in the AD compliance section of the engine maintenance records listed compliance with AD 91-14-22 as "N/A by model number." Review of the text of the AD and SB 475A disclosed that it applied to the Lycoming O-320-E2A engine installed in the airplane.
The crankshaft gear attach bolt loosening and backing out of its crankshaft bore, which led to the fatigue failure of the crankshaft gear dowel pin due to excessive working of the gear. The sequence of failures was the result of the engine overhaul shop's failure to comply with an Airworthiness Directive and the engine manufacturer's Service Bulletin.
Source: NTSB Aviation Accident Database
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