NTSB Factual Report

On July 4, 2011, about 1430 central daylight time, a Cessna 172N, N109DP, registered to and 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 Code of Federal Regulations (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. The flight originated from 0AL1 about 1400.

The pilot-in-command (PIC) stated that the flight departed on the banner tow flight with 48 gallons of 100 low lead (100LL) fuel, and at about the return point of their planned route of the banner tow flight, they began to climb to the north to return to the field. The pilot then noticed a loss of engine rpm and a small vibration, which he attempted to resolve the issues but was unable and reported the engine continued losing power. He then elected to release the banner and maneuvered towards Wolf Field, but was unable to land there. He then maneuvered the airplane for a forced landing in water near shore of Walker Island, and after touchdown, the airplane nosed over. The airplane was recovered for further examination.

Examination of the airframe and engine was performed by a Federal Aviation Administration (FAA) airworthiness inspector-in-charge (IIC). The examination of the airframe revealed the left fuel tank contained 100LL fuel, while the fuel selector was found positioned to the right tank which contained a mixture of 100LL and automotive fuel; but the mixture was mostly automotive fuel. No placards specifying grade of automotive fuel were noted by either fuel filler cap. Inspection of the fuel strainer and carburetor revealed the presence of automotive fuel. The examination of the engine revealed damage to the No. 3 cylinder around the bottom spark plug. Further examination of the engine revealed no discrepancies with the powertrain, air induction, or lubrication systems of the engine. Inspection of the spark plugs revealed all except the No. 3 cylinder exhibited dark discoloration consistent with a rich fuel to air ratio. The magnetos were properly timed to the engine with no discrepancies of the magnetos reported. No discrepancies with the ignition harness was noted with the exception of the No. 3 bottom ignition lead which was heat damaged in the area of the bottom spark plug. The No. 3 cylinder was removed for further examination.

Examination of the operator’s on airport fuel tank was also performed by the FAA-IIC. The FAA-IIC reported that the fuel tank had been serviced by 87 octane automotive fuel with 10 percent ethanol and regionally adjusted additives. No fuel samples were obtained.

Examination of the No. 3 cylinder and piston was performed by the NTSB Materials Laboratory located in Washington, DC. The examination revealed the piston crown contained areas with flaky brittle spatter material. The majority of the damage to the cylinder was around the bottom spark plug hole, and approximately 25 percent of material around the threaded spark plug insert ring was obliterated. Energy dispersive X-ray spectroscopy (EDS) of white spatter contamination revealed the compounds were high in carbon and oxygen as well as elements expected to comprise the casting material of the cylinder head. Testing of the composition of the cylinder head near the bottom spark plug hole revealed the material was consistent with the specified material in the engineering drawing for the casting. Further examination of the cylinder head near the bottom spark plug hole revealed the microstructure was consistent with aluminum alloys having undergone incipient melting. No manufacturing defects were reported in the factual report. A copy of the NTSB Materials Laboratory Factual Report is contained in the NTSB public docket for this case.

The airplane was equipped with a 180 horsepower Lycoming O-360-A4M engine which had been converted from a 150 horsepower O-320-E2D engine. According to type certificate data sheets for the O-320-E2D and O-360-A4M engines, the minimum fuel grade aviation gasoline are 80/87, and 100LL, respectively. After the engine conversion, supplemental type certificates (STC’s) SA2600CE and SE2563CE were installed on the airframe and engine allowing the use of automotive fuel. Paperwork associated with both STC’s specifies that the approved fuel minimum octane rating is 91 and intermixing with aviation gasoline is approved, but fuel containing alcohol is not approved. The STC’s also stipulate that placards by each fuel filler opening are required; the placards specify in part that fuel containing alcohol is not allowed. Copies of the STC’s are contained in the NTSB public docket for this case.

Review of the airframe maintenance records revealed the last 100-Hour inspection was signed off as being completed on the day of the accident. The inspection was performed by the PIC, who also holds a mechanic certificate with airframe and powerplant ratings, and also an inspection authorization (IA). The same person who inspected the airplane on the day of the accident modified the airplane in 2009, allowing the use of automotive fuel. The airplane had been operated for approximately 2.0 hours since the inspection was signed off as being completed.

NTSB Probable Cause

The operation of the airplane using unapproved fuels, which resulted in abnormal combustion and subsequent damage to the No. 3 cylinder. Contributing to the accident was the inadequate 100-hour inspection because the mechanic failed to note the lack of placards by either fuel filler cap specifying the minimum automotive fuel grade and no alcohol allowed as specified by the installed STC’s.