CHIMACUM, WA, USA
N8469N
BEECH V35A
During flight the pilot encountered an engine vibration, and shortly thereafter oil began appearing on the windscreen. While maneuvering toward suitable terrain the #2 cylinder departed the aircraft. A forced landing was made to a field. The aircraft impacted several fence posts, and the landing gear collapsed as it traversed rough/uneven terrain. Engine records documented a top overhaul of the engine approximately 172 hours before, during which the cylinders were removed and replaced. Metallurgical examination revealed that several cylinder hold-down nuts had backed off their bolts, or the bolts had separated in fatigue, allowing the cylinder to break free of the engine case. The mechanic reported using a silicone sealant between the cylinders and their respective engine case halves. Application of the uncalled-for sealant between the cylinders and case halves could result in a reduction or elimination of the preload torque applied to the through-bolts and hold-down studs.
On August 13, 1995, approximately 2020 hours Pacific daylight time, a Beech V35A Bonanza, N8469N, was substantially damaged during a collision with fence posts during an emergency landing following a total loss of power in cruise. The forced landing occurred near Chimacum, Washington, and the commercial pilot and two of the three passengers received minor injuries. The remaining passenger was uninjured. Visual meteorological conditions prevailed and no flight plan had been filed. The flight, which was personal, was to have been operated under 14CFR91, and originated from Olympia, Washington, approximately 2000. The pilot reported that approximately 15 minutes into the flight an engine vibration developed and shortly thereafter oil began appearing on the aircraft's windscreen. He then maneuvered the aircraft toward more suitable landing areas as he was over water and timbered terrain. Shortly thereafter the number two cylinder departed the aircraft and engine power was lost. The pilot set up for an emergency landing in a field and lowered the landing gear and flaps in preparation for landing. During the landing rollout the aircraft collided with several fence posts and the gear collapsed as it traversed uneven terrain. The engine was disassembled on August 24, 1995, at the facilities of AVSTAR Aircraft, Pierce County Airport, Puyallup, Washington. Several bolts and retaining hardware associated with the absent number 2 cylinder were retained for further metallurgical examination. Cylinders one, and two through six were removed from the engine case halves. All five cylinders displayed an orange silicone type sealant material between the flanges and their respective case halves (refer to photographs 1/2). Additionally, numerous fragments from the number two piston were found in the bottom of the engine cowling and within the oil sump pan (refer to attached Teledyne Continental Engine Disassembly Report). Metallurgical examination of several bolts and nuts which secured the number two cylinder to its engine case half as well as the fragments of the number two piston revealed the following (refer to DIAGRAM I): A number of adjacent threads on one end of the lower forward through-bolt (#1, DIAGRAM I) were worn and contained "mushroom" deformation. Several of the threads within the nut associated with the number two cylinder side of the bolt were stripped and the washer face of the nut (cylinder hold-down side) appeared polished. The upper forward through-bolt (#2, DIAGRAM I) was broken through the threaded area (#2 cylinder side) and the separated surface revealed fatigue propagation through approximately 75 percent of the bolt. A fatigue propagation similar to the that described for the upper forward through-bolt was evident on the one retrieved hold down stud which had its associated nut still engaged (#3, DIAGRAM I). An additional nut from an unidentified hold-down stud exhibited the same polishing described for the lower forward through-bolt nut. Examination of the number two piston fragments revealed no evidence of pre-existing fracture areas. The aircraft's engine had accrued 171.6 hours since a top overhaul conducted on November 1, 1993. At that time, all six cylinders were removed, underwent a cermichrome process, and were re-installed. The facility which performed the overhaul was JRW Maintenance at the Olympia Airport, Olympia, Washington (refer to ATTACHMENT MR-I and EL-I). The mechanic who performed the overhaul was interviewed by FAA inspectors on October 11, 1995, and reported that he "put the silicone around the cylinders of the engine to stop leaks around the base of the cylinders" (refer to ATTACHMENT S-I). The 1992 Teledyne Overhaul Manual for the IO-520 series engines requires the installation of "new packing on each cylinder skirt" but makes no reference as to the use of any unapproved sealants (e.g., silicone). Additionally, the eight nuts associated with the cylinder's four through-bolts and four hold-down studs are to be tightened to a specified torque when replacing the cylinder. Application of a sealant between the cylinder flange and engine case could compromise the assurance of proper torquing of the nuts and result in their backing off at some future time.
the improper top overhaul of the engine and subsequent release of the cylinder hold-down nuts/breakage of hold-down and through-bolts. Factors contributing to the accident were the fence posts and rough/uneven terrain.
Source: NTSB Aviation Accident Database
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