Incident Overview
On February 12, 2011, at approximately 1150 eastern standard time, a Cessna 150L airplane, registration N6622G, sustained substantial damage during a forced landing near Trenton, Michigan. The commercial pilot, the sole occupant, reported no injuries. The airplane was operated by Drake Aerial Enterprises, LLC under 14 CFR Part 91 as a banner towing flight. Visual flight rules (VFR) conditions prevailed, and no flight plan was filed. The flight originated from Oakland/Troy Airport near Troy, Michigan, around 1100, with a destination of Grosse Ile Municipal Airport near Grosse Ile, Michigan.
Aircraft and Flight Details
The airplane, a 1970 Cessna 150L (serial number 15072122), was an all-metal, high-wing, semimonocoque design. It was powered by a Lycoming O-360-A4A engine (serial number L-28947-35A) installed under supplemental type certificate SA4795SW, documented on a major repair and alteration form dated December 8, 2003. Maintenance was conducted under an annual inspection program, with the most recent inspection completed on February 7, 2010. The airframe had accumulated 8,201 total hours, and the engine had 2,836 hours since overhaul.
According to the operator's report, the pilot had been towing a banner for about 55 minutes when he felt a heavy vibration and heard a loud bang. The airplane instantaneously lost power, and the pilot could not keep the engine running. He released the banner over an area away from people and structures and executed a forced landing. During the landing, the nose landing gear collapsed upon contacting heavy snow and unimproved terrain, causing the firewall to bend and resulting in substantial damage.
Postaccident Examination
Examination of the engine revealed that the number four connecting rod had separated from its crankshaft. One of the two corresponding connecting rod bolts was deformed, with its associated nut separated from the bolt and appearing undamaged. The second connecting rod bolt was fractured near the midpoint of the shank. Metallurgical examination of the fracture surface showed features consistent with overstress separation.
Relevant Maintenance Information
Lycoming Service Bulletin No. 240W, titled "Mandatory Parts Replacement at Overhaul and During Repair or Maintenance," states that at overhaul or upon removal, stressed bolts and fasteners such as connecting rod bolts and nuts must be replaced regardless of their apparent condition. The operator indicated that the installed connecting rod bolts and nuts were new when the last maintenance was performed on that cylinder.