WPR09LA245

In cruise flight, the airplane experienced a loss of power to the avionics. While focusing on that situation, the pilot reported a partial loss of engine power and the inability of the airplane to maintain altitude. The pilot elected to make a precautionary landing at a nearby airport. Believing he was in gliding distance of the airport, he shut down the engine. The approach was too high and the airplane overshot the runway. The pilot attempted a turn back to the runway; however, he had to make a sharper-than-normal turn due to wires in his immediate flight path. While performing the tighter turn, the airplane lost further altitude and the pilot had to make a forced landing adjacent to the runway on uneven terrain, coming to rest inverted. During a postaccident examination of the engine it was discovered that the number one cylinder's intake valve had deposits on the valve seat, preventing it from making a tight seal and resulting in the partial loss of engine power. No electrical problems could be identified during the examination.

HISTORY OF FLIGHT On May 16, 2009, about 1630 Pacific daylight time, a Cessna 172N, N738LF, experienced a partial loss of engine power and collided with terrain during the precautionary landing near Iron Mountain Pumping Plant Airport, Desert Center, California. The airplane sustained substantial damage during the accident sequence, coming to rest inverted. California Flight Academy was operating the airplane under the provisions of 14 Code of Federal Regulations (CFR) Part 91. The private pilot and one passenger were not injured. The local personal flight departed Gillespie Field, San Diego, California, about 1415. Visual meteorological conditions prevailed, and a visual flight rules (VFR) flight plan had been filed. The pilot reported that after departing El Cajon he was maneuvering the airplane over the desert when it experienced a loss of power to the avionics and he could no longer make or receive radio transmissions. The fuel gauges then indicated that the fuel tanks were empty, and he noticed the airplane was unable to maintain altitude due to a partial loss of engine power. The pilot performed an off-airport landing on the open desert terrain about a mile from a small airstrip. After the airplane touchdown it encountered uneven terrain and nosed over. The operator's chief pilot reported that he spoke with the pilot following the accident. The chief pilot relayed a summary of the interview; while in cruise flight at 7,500 feet mean sea level (msl), the engine experienced a loss of power. In response, the pilot elected to make a precautionary landing at a nearby private airport. Believing he was in gliding distance to the airport, the pilot shut off the engine by turning the fuel selector to "off" and fully retarding the mixture control. He overshot the runway and maneuvered the airplane in a left turn in an attempt to circle back toward the runway. During the turn, he observed power lines in his flight path, and began to steepen the left bank. The airplane's altitude rapidly decreased and he was forced to land adjacent to the runway. In the chief pilot's written submission to the Safety Board (NTSB Form 6120.1, Pilot/Operator Aircraft Accident/Incident Report), in the section titled RECOMMENDATION (How could this accident/incident have been prevented), he stated that the accident pilot needed "more training and testing on abnormal procedures." He further stated that "a complete electrical failure is not an emergency situation in VMC conditions and should not lead to an off field landing." The pilot reported no preimpact mechanical malfunctions or failures with the airframe or engine. TESTS AND RESEARCH Following recovery, investigators examined the airplane at the storage facility of Air Transport, Phoenix Arizona, on June 27, 2009. Accompanying a Safety Board investigator was a representative from Textron Lycoming. The engine representative removed the top spark plugs, which were clear from debris and showed no evidence of mechanicaldeformation. The spark plug electrodes were gray in color, which corresponded to normal operation according to the Champion Aviation Check-A-Plug AV-27 Chart. A borescope examination on all cylinders found no foreign object damage, no evidence of detonation, and no indication of excessive oil consumption. The number one cylinder's intake valve had deposits on the valve seat, which appeared to prohibit it from closing completely. Investigators manually rotated the engine, establishing internal mechanical continuity during rotation of the crankshaft and upon attainment of thumb compression. The number one cylinder had lower pressure and gave less resistance than the other cylinders. Based on the unequal cursory compression check, investigators performed a differential compression check. The results were as follows: number one 14/80; number two 77/80; number three 75/80; and number four 73/80. During the testing of the number one cylinder, air was heard leaking from the carburetor. No electrical problems could be identified.