14 CFR Part 91: General Aviation
Accident occurred Friday, May 11, 2012 in Rexburg, ID
Probable Cause Approval Date: 10/09/2014
Aircraft: CHAMPION 7GC, registration: N4861E
Injuries: 2 Uninjured.
NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.
The owner/pilot had completed two touch-and-go landings in the tailwheel-equipped airplane at his home airport and then left the airport traffic pattern to overfly a property south of the airport. For the overflight, the pilot reduced the engine rpm to about 2,100 and operated at an altitude of several hundred feet above the ground. The pilot then noticed that the oil pressure indication had dropped to the bottom of the green arc. He increased the engine rpm but observed the oil pressure continue to decrease. He considered attempting to return to the airport but then decided against that due to the population density between the airport and his current position; he elected to conduct a precautionary landing in a field. On short final for the field, the pilot failed to see the power lines across the field. The airplane struck the power lines then landed hard in the field. Postaccident examination of the airplane and engine did not reveal any mechanical abnormalities or conditions that would account for the decreased oil pressure indication, and when the engine was rotated with the starter, the oil pump was observed to produce expected pressure on the gauge and to pump oil.
The National Transportation Safety Board determines the probable cause(s) of this accident as follows:
A decrease in indicated oil pressure while maneuvering at low altitude for reasons that could not be determined because postaccident examination did not reveal any anomalies that would have precluded normal operation. Also causal was the pilot’s failure to maintain clearance from power lines during the precautionary landing to a field.
HISTORY OF FLIGHT
On May 11, 2012, about 1810 mountain daylight time, a Champion 7GC, N4861E, was substantially damaged when it struck power lines during a precautionary landing following a loss of engine oil pressure near Rexburg, Idaho. The pilot/owner and his passenger were uninjured. The personal flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no flight plan was filed for the flight.
According to the pilot, he departed the traffic pattern of Rexburg-Madison County Airport (RXE), Rexburg, after conducting two touch-and-go landings. He headed south, and reduced the throttle to 2,100 rpm to overfly a property. At that time, when the airplane was only a few hundred feet above ground level, the pilot noticed that the oil pressure indication had dropped to the bottom of the green arc. He increased the engine to 2,500 rpm, and observed that the oil pressure indication decreased into the upper end of the yellow arc. The pilot considered a return to RXE, but then decided against that due to the population density between the airport and his current position, and elected to conduct a precautionary landing in a field. On short final for the field, the airplane struck power lines that were strung to a pump in the field, and then landed hard in the field. The airplane skidded about 150 feet, and came to rest upright. The propeller, landing gear and fuselage were damaged.
PERSONNEL INFORMATION
Federal Aviation Administration (FAA) information indicated that the pilot held a private pilot certificate with an airplane single-engine land rating. The pilot reported a total flight experience of 295 hours, including 149 hours in the accident airplane make and model. His most recent FAA third-class medical certificate was issued in November 2011, and his most recent flight review was completed in November 2011.
AIRCRAFT INFORMATION
The airplane was manufactured in 1959, and was equipped with a Lycoming O-320 series engine. The engine was manufactured in 1965, and had a total time in service of 1,289 hours. Per Lycoming Service Instruction 1009, the recommended overhaul interval for the engine was 2,000 hours in service, or 12 calendar years, whichever comes first. Although the engine had exceeded the manufacturer's recommended overhaul interval by a factor of more than threefold in calendar year, the engine had never been overhauled.
According to the Lycoming operator's manual, normal engine oil pressure is 25 pounds per square inch (psi) at idle speed. In the normal engine operating speed range, minimum allowable oil pressure was 60 psi, and maximum was 90 psi. That range would be denoted by a green arc on the oil pressure indicator gauge.
METEOROLOGICAL INFORMATION
The pilot reported that the 1753 automated weather observation for RXE included winds from 195 degrees at 4 knots, clear skies, temperature 17 degrees C, dew point -7 degrees C, and an altimeter setting of 30.11 inches of mercury.
WRECKAGE AND IMPACT INFORMATION
The airplane came to rest upright in a field, about 3 miles south-southeast of the airport. Both main landing gear struts were deformed up and aft, so that the fuselage rested on the ground. The cowling and firewall were deformed/crushed up and aft, and both propeller blades of the all-metal propeller were bent aft.
About a month after the accident, the airplane and engine were examined by an NTSB and a Lycoming investigator. There were no indications of any oil leakage from the engine. The spark plugs were pulled and they appeared to be in good condition. A thumb compression check was accomplished, with no abnormalities noted. The engine exhibited continuity throughout its drive train.
Electrical power was supplied to the airplane, and the starter turned the engine over normally. Oil pressure was noted in the cockpit; the gauge indicated 30 psi, which was in the yellow range of gauge, but is a normal value when the engine is turning at below-idle speed. The engine was not started due to the bent propeller blades, and the possibility of unobserved internal damage. The oil line was disconnected and oil was observed to be pumped when the engine was cranked by the starter. No abnormalities with the engine's oil system were noted. The oil quantity was not determined, and no further examination or testing of the engine, oil system, or oil pressure indicating system was accomplished.
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