Accident Overview
On July 15, 2008, at approximately 1220 eastern daylight time, a Piper PA-18-150, registration N4287Z, operated by Sky Signs LLC, was substantially damaged during a forced landing near Surfside Beach, South Carolina. The certificated commercial pilot sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the local banner-tow flight, which had departed from a private airfield in Conway, South Carolina. The flight was conducted under 14 Code of Federal Regulations Part 91.
Pilot Actions and Engine Failure
According to a written statement from the pilot, he arrived at the departure airport around 0700 to begin a routine day of banner towing. A preflight inspection of the airplane included filling both fuel tanks and checking the oil. The pilot reported that a "nominal" level of oil was visible on the dipstick, and no abnormalities were noted. Following an uneventful three-hour flight, the pilot returned to the departure airport to refuel and again check the engine oil level. He departed again at about 1205, retrieved a banner, and proceeded to his assigned route.
Around 1215, the pilot noticed a slight vibration emanating from the engine, which within seconds became a "very intense" vibration. Engine power began to diminish rapidly. The pilot notified the local air traffic control tower and began searching for a suitable forced landing site. During the descent, he attempted to restore engine power by switching from the right to left fuel tank, toggling the magnetos from "BOTH" to "LEFT," then "RIGHT," then back to "BOTH," and applying carburetor heat. None of these efforts restored power. After selecting a landing area, the pilot maneuvered the airplane and dropped the banner in a safe location. During the landing, the wheels encountered soft ground, causing the airplane to nose over and sustain substantial damage.
Maintenance History and Post-Accident Examination
Review of maintenance logs revealed that the engine had been field overhauled and reinstalled on the airplane on July 8, 2008, accumulating 27 total hours of operation since that date. Post-accident examination of the engine found compression on all cylinders, spark plugs in "new" condition, and magnetos producing spark at all terminal leads with timing set as prescribed on the data plate. No metal contamination was observed in the engine oil screen. However, examination of the carburetor box revealed that the carburetor heat "flapper" was only free to move through half of its travel range. Disassembly of the box showed that the flapper travel was obstructed by a mud dauber's nest.
Weather Conditions
At 1150, the recorded weather at Myrtle Beach International Airport (MYR), approximately 5 nautical miles northeast of the accident site, included winds from 050 degrees at 13 knots, visibility 7 statute miles, clear skies, temperature 29°C, dew point 17°C, and an altimeter setting of 30.08 inches of mercury. Using the ambient temperature and dew point, a carburetor icing probability chart from the National Research Council of Canada indicated a probability of "serious icing at glide power," while a chart in the Federal Aviation Administration Tips on Winter Flying pamphlet indicated "light icing - glide or cruise power."