FTW99LA206

While in cruise flight at 10,500 feet msl, the pilot smelled a strong odor of fuel, and observed that the fuel pressure gauge needle had dropped almost to zero. The pilot switched fuel tanks and turned on the electric fuel pump. This did not increase the fuel pressure, and a strong odor of fuel persisted. The pilot initiated a forced landing to the nearest airport, but landed in an open field 1/4 mile short of the runway and subsequently, impacted a fence. Examination of the fuel system after the accident revealed that the fuel hose that ran between the fuel pump and the fuel injector servo was disengaged from the coupling at the fuel pump. Examination of the coupling revealed that a portion of the first thread was separated as a result of fatigue.

On July 30, 1999, at 1600 central daylight time, a Mooney M20J single-engine airplane, N91FH, registered to and operated by the Nacogdoches Gospel Assembly Church of Nacogdoches, Texas, was substantially damaged during a forced landing following a partial loss of engine power near Mount Pleasant, Texas. The private pilot and his passenger were not injured. Visual meteorological conditions prevailed, and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 business cross-country flight. The flight departed Aurora, Missouri, at 1400, with a destination of David Wayne Hooks Memorial Airport, Spring, Texas.

During a telephone interview, the pilot reported to the NTSB investigator-in-charge that while in cruise flight at 10,500 feet msl, he smelled a "strong" odor of fuel and observed that the fuel pressure had dropped almost to zero. The pilot switched fuel tanks, and turned on the electric fuel pump. The needle on the fuel gauge did not increase, and the strong odor of fuel persisted. The pilot diverted toward the Mount Pleasant Municipal Airport with the engine operating at idle. While on final approach to runway 17, he applied throttle to adjust the aircraft's rate-of-descent; however, it had no effect on the engine rpm. A forced landing was executed to an open field approximately 1/4 mile short of the runway.

The pilot stated that the airplane touched down near the middle of the field, and during the landing roll, the airplane impacted a fence and came to a rest upright. The pilot added that after exiting the aircraft, he observed fuel leaking from the right fuel tank.

Examination of the airplane by an FAA inspector revealed that the right wing was displaced aft, and the airplane's fuel tanks were empty. The FAA inspector stated that the airplane's cabin had the odor of fuel.

Further examination revealed that the fuel hose that ran between the engine driven fuel pump and the fuel injector servo was separated from the coupling at the fuel pump. The B-nut and coupling that attached the fuel hose to the fuel pump remained secure. The fuel hose and the coupling were removed from the accident aircraft for further examination.

The fuel hose and the separated coupling were examined at the NTSB Materials Laboratory in Washington, D.C. Examination of the coupling revealed that a portion of the first thread was missing and a fractured surface, extending around two-thirds of the circumference of the thread, was visible. The coupling was ultrasonically cleaned and examined with a scanning electron microscope (SEM). The fractured surface contained radial marks and crack arrest positions emanating from the root of the thread, which are typical of fatigue cracking. There were multiple origins along the root of the thread that propagated towards the inside diameter of the tube and extended through the wall thickness of the thread.

The mating threads inside the fuel hose were examined with a borescope, and there were signs of wear on all threads. The fractured portion of the first thread from the coupling was not present between the threads in the fuel hose.

According to the NTSB Pilot/Operator Aircraft Accident Report (NTSB Form 6120. 1/2), the aircraft and engine had accumulated 1,000 hours total time. Review of the engine maintenance records revealed that on April 15, 1999, the Lycoming IO-360-A386D engine (s/n: L-25601-51A) underwent a 100-hour inspection at an engine time of 905.7 hours total time.