Accident Circumstances
The aircraft collided with ground obstructions and nosed over during a forced landing on a dirt road at night. The forced landing occurred after a catastrophic engine failure during cruise.
Engine Examination
A large hole was found in the engine case on each side of the upper spine between cylinders 1 and 2. The oil pan was removed, and its contents included a fragmented crankshaft counterweight, two counterweight pins, four retaining plates, and five snap rings. Two of the retaining plates were bent and distorted; three snap rings were distorted. Among the remaining three counterweight assemblies, the No. 1 trailing weight on crank cheek 2 was correctly installed. The No. 3 trailing weight on crank cheek 5 was partially retained by only the forward pin, with the aft pin and associated retaining plate and snap ring missing; these were later found in the oil sump. The forward pin remained in place, with one snap ring correctly installed and one not. The No. 4 leading weight on crank cheek 5 was intact and correctly installed.
Inspection and Maintenance History
FAA AD 99-09-17, issued April 22, 1999, mandated compliance with Continental Mandatory Service Bulletin (MSB) 99-3, which required visual and ultrasonic inspections of the crankshaft for cracks. The inspection was performed on May 4, 1999, 220 flight hours before the accident. To prepare the engine, cylinders 1 and 3, and all four crankshaft counterweights were removed. The operator's mechanic performed the removal and reinstallation of components after a factory representative conducted the inspection. The mechanic worked through the 5.5-inch cylinder base openings, and the work was inspected and signed off by a company inspector at each stage.
Three versions of MSB 99-3 were issued. MSB 99-3A was current at the time of inspection. MSB 99-3B and 99-3C, issued July 6 and 27, 1999 respectively, incorporated guidance on counterweight pin retainer plate and snap ring installation. An additional Service Bulletin, SB 00-3, issued February 2, 2000 (13 days before the accident), provided detailed procedures for reinstallation of counterweights, including correct orientation and installation of pins, retainer plates, and snap rings. The engine overhaul manual and other references available to the mechanic at the time did not detail these critical installation steps.
No Evidence of Oil Starvation
Examination of the engine found no evidence of oil starvation or exhaustion, or any other internal anomaly beyond the separation of the No. 2 leading counterweight that would have led to the catastrophic destruction of the engine.