MIA99LA191

The flight was in cruise at 6,500 feet msl, when the engine started to run rough. Two to three minutes later the engine stopped operating, and the pilot requested vectors to the nearest airport. While setting himself up for a forced landing, the cabin filled with smoke, and the pilot cracked open the cabin door to evacuate the smoke. The airplane touched down short of the runway and sustained main landing gear damage. Postcrash examination revealed muffler and muffler shroud breaching that allowed engine exhaust to impinge on and burn components of the nose landing gear, the air induction system, and the lower fuselage. NTSB Materials Laboratory examination revealed the muffler failed due to scaling and intergranular attack occurring over a period of time that would have been evident 30 flight hours previous when the airplane underwent an annual inspection.

On June 29, 1999, about 1240 eastern daylight time, a Mooney M20F, N7114V, registered to a private individual, operating as a Title 14 CFR Part 91 personal flight, crashed short of the runway at Causey Airport, Liberty, North Carolina. The pilot was attempting a forced landing following an in-flight engine failure and subsequent smoke in the cabin. Visual meteorological conditions prevailed and no flight plan was filed. The airplane sustained substantial damage and the private-rated pilot, the sole occupant, was not injured. The flight originated from Newport News, Virginia, about 1 hour 10 minutes before the accident.

According to the pilot, he was in cruise flight at 6,500 feet msl, when he heard the engine start to run rough. Two to 3 minutes later, the engine stopped altogether, and he steered toward the Causey Airport for a forced landing. He was in the landing pattern when the cabin filled with smoke. He touched down short of the runway into rough terrain, causing damage to the landing gear. In follow-up phone conversation, he stated he does not remember hearing any unusual engine noises during start or en route, nor does he remember any increase of level of exhaust noise. He did say, however, that he uses noise attenuating earphones that are very effective.

According to an FAA inspector, the airplane touched down 300 feet short of the runway and hit a berm, shearing the right main landing gear assembly and fracturing the left wheel at the axle. Postcrash examination revealed that in addition to the main gear damage, the nose tire was burned and deflated, and the fuselage bottom aft of the firewall was heat stressed and cracked. The muffler shroud had a 2 x 3 inch hole and the muffler had a 4 x 4 inch hole blown out of their respective side walls and welded seams. Portions of the lower plenum/air induction system were melted.

The muffler and shroud were shipped to the NTSB Materials Laboratory for failure analysis examination. The muffler walls revealed scaling and intergranular attack that eventually became cracks, and in the case of the perforated inlet pipes, disintegration. This allowed the undiffused exhaust gases to directly impinge on the muffler walls, accelerating the aging process.

The Mooney M20 Series Service and Maintenance Manual and 100-Hour Annual Inspection Guide state that the exhaust heater shroud should be removed and inspected and the muffler inspected for corrosion, fatigue and/or welding cracks, and any other apparent damage during annual inspections. According to airplane maintenance records, this engine and airframe underwent an annual inspection on January 21, 1999, and had accumulated 30 hours since the inspection.