Accident
On April 5, 2011, at about 1700 Pacific daylight time, an amateur-built experimental Zenith 701, registration N128CF, experienced a partial loss of engine power during the initial climb after takeoff from a private airstrip near El Centro, California. The pilot initiated a forced landing to a wet, muddy wheat field. During the landing roll, the nose wheel submerged in the soft terrain, causing the aircraft to nose over. The accident resulted in substantial damage to the vertical stabilizer and left wing root. The private pilot was not injured, and the passenger sustained minor injuries. Visual meteorological conditions prevailed, and no flight plan was filed for the local personal flight.
Investigation
The aircraft was operated by the pilot under 14 CFR Part 91. At the time of the accident, the airframe and engine had accumulated 44 total hours. No aircraft maintenance records were located during the investigation.
On June 17, 2011, a preliminary examination of the recovered engine by the pilot and a Federal Aviation Administration (FAA) inspector revealed visible damage to the number two cylinder wall and piston after the exhaust stack was removed. The engine was subsequently removed and shipped to Recreational Power Engineering in Tiffin, Ohio, for further inspection.
On October 24, 2011, an inspection of the three-cylinder Hirth 3701 engine, serial number 898687, was conducted by a representative of Recreational Power Engineering under FAA supervision. The number two piston exhibited signatures consistent with overheating, with the piston pin and underside of the piston head showing a blue discoloration. The piston rings were seized in their lands and worn smooth, indicating oil starvation to that cylinder. Examination of the oil pump system revealed that the number one shaft/bearing assembly was intact and operational, but the number two drive coupling was found damaged, out of alignment, and non-functional. According to the representative, this condition would cause the oil pump to supply oil at a sporadic rate below minimal volume and pressure, leading to oil starvation primarily to the number two cylinder assembly. No evidence of a failure of the number two oil supply tube was found. The reason for the failure of the oil pump drive coupling was not determined.