Accident Overview
On May 31, 2008, at approximately 1115 eastern daylight time, a Piper PA-18-135, registration N802DA, was substantially damaged after impacting trees during a forced landing near Myrtle Beach, South Carolina. The certificated commercial pilot, who was the sole occupant, received minor injuries. The aerial banner tow flight was operated by SC Sky Signs under 14 CFR Part 91. Visual meteorological conditions prevailed, and no flight plan was filed.
Flight History
The pilot departed the operator's private grass airstrip in Conway, South Carolina, about 1058, intending to fly to and along the shoreline. After leveling at around 1,000 feet, he informed the Myrtle Beach International Airport (MYR) air traffic control tower that he had crossed the extended centerline of runway 36. Shortly thereafter, he noticed his altitude had decreased to 900 feet, applied power, and climbed back to 1,000 feet.
Soon after, the pilot observed the engine oil temperature increasing and felt the engine losing power. He communicated with MYR tower and requested a 180-degree turn back to his home airport. During the turn, oil pressure fell and oil temperature continued to rise. Realizing he could not reach either the departure airport or MYR, he planned an off-airport landing. He identified a street in a housing development as a potential site and set up a right traffic pattern. At approximately 400–500 feet above ground, he spotted a clearing and released the banner. He then requested that MYR tower notify fire/rescue authorities of his forced landing. While on downwind for the selected site, the engine quit; lacking altitude to reach it, he chose a second site, but the wings impacted trees before touchdown.
Engine and Maintenance Findings
According to FAA records, the aircraft was manufactured in 1953 with a Lycoming O-290 engine but was equipped with a Lycoming O-320 engine at the time of the accident. No logbooks were made available. Documentation of the engine change was incomplete; a supplemental type certificate (STC SA00522SE) existed for the O-320 installation but no continuous chronology of engines was found.
An examination of the engine at the operator's facility revealed that the No. 4 cylinder, piston, and rings were heat damaged. The piston head showed a coloration pattern typical of detonation, and the wrist pin had bluing, indicating exposure to abnormally high operating temperatures. The oil pump was initially frozen but later rotated freely. Other components showed normal wear to minor scoring.
Lycoming guidance indicated that operating on the lean side of peak exhaust gas temperature (EGT) is not recommended for engines with float-type carburetors, as was the case. The STC for the O-320 engine did not include fuel mixture guidance. The Piper Super Cub Owner's Handbook contained only a general sentence on mixture control.
Pilot and Operator Procedures
The pilot had approximately 840 total flight hours, with 120 in the accident make and model. He reported 126 hours in the preceding 90 days. His most recent flight review was on February 28, 2008, and his medical certificate was issued April 1, 2008.
The pilot stated the aircraft had no fuel flow or EGT gauge. The operator instructed him to lean the mixture by reducing it until the engine began to miss, then enrichen until smooth, followed by a small further enrichment. Cruise power was set to achieve an indicated airspeed of 45–50 mph, with engine rpm varying from about 2,350 to 2,450 rpm depending on banner size. The FAA inspector noted that the pilot generally leaned to a fuel consumption of 6 gallons per hour (gph) in cruise. However, performance data indicated that minimum fuel consumption for typical cruise rpm (2,350–2,450) ranged from 7 to 7.2 gph, suggesting the mixture may have been set leaner than recommended.