Cessna R172K N758FQ accident near Spotsylvania, Virginia

Probable cause

The pilot's failure to follow the checklist and failure to achieve the proper touchdown point during a forced landing. Contributing to the accident was a loss of engine power due to a cracked No. 4 top sparkplug insulator, resulting in pre-ignition/detonation and the failure of the No. 2 connecting rod cap due to evacuation of the oil supply.

NTSB analysis

The pilot stated that he was on an IFR flight plan at 5,000 feet in VFR conditions, and in radio contact with approach control, when the engine started to run a little rough. A short time later, the pilot smelled fuel fumes and he was unable to determine the source. The pilot informed approach control that he needed to land, initiated a forced landing, and the engine stopped less than a minute later. The pilot stated that he elected not to make a traffic pattern. He used 10 degrees of flaps, the airplane touched down long about halfway down the field at about 90 knots, and collided with a fence and trees. Examination of the forced landing area revealed it was 1,050 feet long and other suitable forced landing areas were available in the immediate vicinity. The Pilot Operators Manual stated full flaps were recommended with an airspeed of 65 knots, and the landing distance required was 610 feet. Examination of the landing area revealed the airplane collided with a 3 to 4-foot tall fence pole 900 feet down the forced landing area before colliding with trees. The airplane traveled 1,100 feet before coming to a stop. The engine was transported to the manufacturer and disassembled. Examination of the engine revealed the No. 4 top spark plug insulator was cracked near the electrode. The No. 4 piston exhibited burn through erosion signatures consistent with a pre-ignition/detonation event allowing excessive crankcase pressure. The oil supply was evacuated through the crankcase breather resulting in the failure of the No. 2 connecting rod cap and loss of engine power.

Text from the NTSB. Open the NTSB docket for MIA08LA035 for the full record.