Accident Overview
On July 4, 2011, about 1430 central daylight time, a Cessna 172N, registration N109DP, operated by Gulf Coast Aerial Advertising, Inc., nosed over during a forced landing in water near Orange Beach, Alabama. Visual meteorological conditions prevailed at the time, and no flight plan was filed for the 14 CFR Part 91 banner tow flight from Resort Airport (0AL1), Foley, Alabama. The airplane sustained substantial damage, and the airline transport pilot and commercial second pilot were not injured.
Flight Details
The flight departed from 0AL1 about 1400 with 48 gallons of 100LL fuel. At approximately the return point of the planned route, the pilot-in-command (PIC) noticed a loss of engine rpm and a small vibration. Attempts to resolve the issues were unsuccessful, and the engine continued losing power. The pilot released the banner and maneuvered toward Wolf Field, but was unable to land there. He then executed a forced landing in water near Walker Island. After touchdown, the airplane nosed over.
Examination Findings
The airframe and engine were examined by an FAA airworthiness inspector. The left fuel tank contained 100LL fuel, while the fuel selector was positioned to the right tank, which contained a mixture of 100LL and automotive fuel, with the latter predominating. No placards specifying the grade of automotive fuel were noted by either fuel filler cap. Inspection of the fuel strainer and carburetor revealed the presence of automotive fuel.
Engine examination revealed damage to the No. 3 cylinder around the bottom spark plug. No discrepancies were found with the powertrain, air induction, or lubrication systems. Spark plugs except the No. 3 exhibited dark discoloration consistent with a rich fuel-to-air ratio. The magnetos were properly timed. The No. 3 bottom ignition lead was heat damaged near the bottom spark plug. The No. 3 cylinder was removed for further examination.
Engine and Fuel Analysis
The operator’s on-airport fuel tank had been serviced with 87 octane automotive fuel containing 10 percent ethanol and regionally adjusted additives. No fuel samples were obtained.
Examination of the No. 3 cylinder and piston by the NTSB Materials Laboratory revealed the piston crown had flaky brittle spatter material. About 25 percent of material around the threaded spark plug insert ring was obliterated. Energy dispersive X-ray spectroscopy (EDS) of white spatter contamination showed compounds high in carbon and oxygen, plus elements expected in cylinder head casting material. The cylinder head material near the bottom spark plug hole was consistent with specified casting material, and its microstructure showed incipient melting. No manufacturing defects were reported.
The airplane was equipped with a Lycoming O-360-A4M engine (180 hp), converted from an O-320-E2D (150 hp). The O-360-A4M requires 100LL fuel minimum. Supplemental type certificates (STCs) SA2600CE and SE2563CE allowed use of automotive fuel, with minimum 91 octane, intermixing with avgas approved, but alcohol-containing fuel not approved. Placards at each fuel filler opening are required, specifying that alcohol is not allowed.
Maintenance Records
The last 100-hour inspection was signed off on the day of the accident, performed by the PIC, who holds an A&P certificate with Inspection Authorization. The same person modified the airplane in 2009 to allow automotive fuel. The airplane had operated about 2.0 hours since the inspection.