NTSB Factual Report

On March 21, 2004, at 1243 Pacific standard time, a homebuilt Stanley Glasair SH-2, N309TS, experienced a loss of engine power and impacted a ditch during a forced landing in a field west of the San Luis County Regional Airport, San Luis Obispo, California. The pilot owned and operated the airplane under the provisions of 14 CFR Part 91. The airline transport pilot, the sole occupant, sustained minor injuries; the airplane sustained substantial damage. The personal flight originated at Corcoran, California, about 1215, with a planned destination of San Luis Obispo. Visual meteorological conditions prevailed and a flight plan had not been filed.

In written and verbal statements, the pilot reported that he was receiving visual flight rules (VFR) flight advisories from the Los Angeles Air Route Traffic Control Center while en route to San Luis Obispo. While approaching the airport proximity, he noted that the engine gauges indicated that the oil temperature was rapidly rising. While proceeding directly to San Luis Obispo, he transmitted over the radio that he was experiencing a rough running engine. About 5 miles from the airport, the engine noise became unusually loud, and he declared an emergency due to an engine failure.

The pilot further stated that the sector controller provided a radar vector to the airport, and instructed him to contact the San Luis Obispo Air Traffic Control Tower. While about 1,200 feet above ground level (agl), and 2 1/2 miles from the airport, a small oil fire erupted in the engine compartment. Realizing that he would be unable to make it to the runway, the pilot executed a forced landing in a field; during the landing roll, the airplane impacted a ditch and tumbled.

In a telephone conversation with a National Transportation Safety Board investigator, the Federal Aviation Administration (FAA) inspector reported that responding municipal fire department personnel extinguished the fire, which had burned the firewall and portions of the structure just aft of it. The oil was leaking out of the engine and dripping on the hot exhaust, becoming a catalyst for ignition. Following the accident, the airplane wreckage was transported to the pilot's hangar, where the FAA inspector examined it. He reported that the Lycoming O-360-A1B engine sustained a catastrophic failure, with a hole knocked in the upper case spine above the rear cylinders. He noted that the right rear piston had seized in the number 3 cylinder and its respective connecting rod was broken just above crankshaft rod end flare. The inspector could not identify the rod end cap or the bearing shells. The inspector did not teardown or open the engine for detailed examination of the parts.

The FAA inspector further stated that prior to the accident, the pilot noticed the engine was experiencing excessive oil consumption. In response, the pilot removed a cylinder from the engine and employed an engine shop to change the piston in an effort to alleviate the excessive oil consumption problems. After the maintenance was preformed, the pilot reinstalled the cylinder. He added that sometime prior to the accident the pilot had also modified the engine by installing larger pistons.

According to the FAA inspector, the pilot, who holds neither a repairman, nor an airframe and power plant certificate, was performing most of the maintenance on the airplane. Upon visual examination of the engine, he noted that all of the cylinders were worn and scored.

The owner took the engine to an overhaul facility that had previously performed work on the engine, and they examined it after the accident. The manager of the facility reported that the rod bearing in the number 3 cylinder failed (part number LW-13212). He further stated that he sent the bearing to a lab for metallurgy testing. Despite numerous attempts by a Safety Board investigator, the overhaul facility failed to return any follow-up phone calls requesting information on the internal condition of the engine as found during the teardown.

A reference book about aircraft piston engines, the "Sky Ranch Engineering Manual," states that there are six major causes of bearing distress, which include, "dirt, lack of lubrication, misassembly, misalignment, overloading, and corrosion."

NTSB Probable Cause

The loss of engine power due to the failure of the #3 cylinder piston and connecting rod for undetermined reasons.