CEN11LA182

The pilot had been conducting a banner towing operation for about 55 minutes when he felt a heavy vibration and heard a “loud bang.” The airplane's engine subsequently lost power, and the pilot executed a forced landing. During the forced landing, the nose landing gear collapsed when it contacted "heavy snow and unimproved terrain," resulting in substantial damage to the firewall. A postaccident examination of the engine revealed that one of the connecting rods had separated from the crankshaft. Metallurgical examination determined that one of the two connecting rod bolts had failed in overstress. The second connecting rod bolt was deformed but otherwise intact; its associated nut had separated from the bolt and was undamaged. The lack of damage to one of the connecting rod nuts in conjunction with the overstress failure of the opposing bolt was consistent with a loss of installation torque on the intact nut. The engine had accumulated 2,836 hours since overhaul. The operator did not supply engine overhaul maintenance records but provided a statement indicating that the installed bolts and nuts were new at the engine cylinder's last maintenance (an engine manufacturer service bulletin instructs that connecting rod bolts and nuts be replaced any time they are removed). However, due to the lack of maintenance records and the number of hours since last overhaul, the investigation could not conclusively attribute the loss of preload torque to the overhaul operation.

On February 12, 2011, about 1150, eastern standard time, a Cessna 150L airplane, N6622G, was substantially damaged during a forced landing near Trenton, Michigan, following an in-flight loss of engine power. The commercial pilot, the sole occupant on board the airplane, reported no injuries. The airplane was registered to and operated by Drake Aerial Enterprises, LLC under the provisions of 14 Code of Federal Regulations Part 91 as a banner towing flight. Visual flight rules (VFR) conditions prevailed for the flight, which was not operating on a flight plan. The local flight departed from the Oakland/Troy Airport, near Troy, Michigan, about 1100, and was destined for the Grosse Ile Municipal Airport, near Grosse Ile, Michigan. The operator's accident report stated that the pilot was flying the airplane with a banner in tow for about 55 minutes when the pilot felt a heavy vibration and heard a loud bang. The airplane "instantly" lost power and the pilot was unable to "keep the engine running." He released the banner over an area away from people and structures and performed a forced landing. During the forced landing the nose landing gear collapsed when it contacted "heavy snow and unimproved terrain." Substantial damage occurred when the collapsed nose landing gear bent the firewall. The airplane was a 1970 Cessna 150L, serial number 15072122, was an all-metal, high-wing, semimonocoque design airplane. The airplane was powered by a Lycoming O-360-A4A, serial number L-28947-35A, installed under supplemental type certificate SA4795SW. The installation was documented on a major repair and alteration form, dated December 8, 2003. The airplane was maintained under an annual inspection program and the operator reported that the airplane’s most recent annual inspection was conducted on February 7, 2010. The airplane reportedly accumulated 8,201 hours of total time and the engine accumulated 2,836 hours since overhaul A postaccident examination of the engine revealed that the no. four connecting rod had separated from its crankshaft. One of the two corresponding connecting rod bolts was deformed. However, the associated nut had separated from the bolt and appeared undamaged. The second connecting rod bolt was fractured near the midpoint of the shank. Metallurgical examination of the fracture surface revealed features consistent with overstress separation. The Lycoming Service Bulletin No. 240W, Mandatory Parts Replacement at Overhaul and During Repair or Maintenance, in part, stated: AT OVERHAUL OR UPON REMOVAL: ... Any time the following parts are removed from any Lycoming reciprocating engine, it is mandatory that the following parts be replaced regardless of their apparent condition: ... Stressed bolts and fasteners, such as: ... Connecting rod bolts and nuts The operator indicated that the installed connecting rod bolts and nuts were new when the last maintenance was performed on this cylinder.