CEN17LA316

The flight instructor and private pilot had completed training maneuvers and were returning to the airport when the engine experienced a partial loss of power about 1,000 to 1,500 ft above ground level. They were unable to glide the airplane to an open field and descended into a wooded area. The airplane impacted trees and became wedged between trees, suspended above the ground. The engine and empennage separated from the rest of the airplane and came to rest on the ground nearby. The fuel tanks were damaged and most of the remaining fuel spilled onto the ground. A postaccident examination of the engine revealed no pre-impact anomalies that would have precluded normal operation or production of rated horsepower; however, an examination of the gascolator showed that it had been leaking fuel from three locations and contained a significant amount of debris. In a postaccident examination, the gascolator was subjected to the relevant service bulletin testing and did not pass the test due to the leaking seals and drain valve. Since the gascolator was unable to seal properly, it would have allowed air into the fuel system, which would have resulted in a loss of engine power. A review of the airplane maintenance records revealed no record of compliance with the service bulletin, nor was compliance mandatory.

On August 11, 2017, about 1200 eastern daylight time, a Navion G airplane, N249KC, impacted trees after a loss of engine power near Adrian, Michigan. The flight instructor and private pilot were seriously injured and the airplane sustained substantial damage. The airplane was registered to Kalea Co. LLC and operated by Sky Walker Flying under the provisions of Title 14 Code of Federal Regulations Part 91 as an instructional flight. Visual meteorological conditions prevailed at the time of the accident and a flight plan had not been filed. The local flight departed Lenawee County Airport (ADG), Adrian, Michigan, about 1000. According to the flight instructor, the engine experienced a loss of power about 1,000 ft above ground level (agl) while over a wooded area and she was unable to glide the airplane to a nearby field. She stated to the sheriff's office that after the accident she walked to a nearby road and waited for a car to pass by for help. The private pilot stated to the sheriff's office that he was flying the airplane and they were returning to the airport after completing training maneuvers. He stated that the engine experienced a partial loss of power about 1,500 ft agl. He added that the engine still had a little power available during the event. The responding Federal Aviation Administration (FAA) inspector reported that the airplane was found wedged between trees with the empennage separated from the rear fuselage and engine separated from the firewall (figure 1). There was a smell of aviation fuel at the accident site. Figure 1 – The airplane suspended above the ground and wedged between trees A postaccident examination of the airplane was conducted by the FAA inspector and a technical representative from Continental Motors. The examination revealed that more than 4 gallons of fuel was drained from left wing tip tank, which remained intact. The right wing tip tank was found breached and had separated from the wing; there was no fuel present in the tank. The fuel gascolator, which is the low point of the center main fuel tanks, did not contain any fuel. There were fuel stain marks underneath the gascolator as it was installed on the airplane. The gascolator was removed for further testing. An examination of the engine revealed the engine sustained impact damage concentrated mostly to the left rear side and the crankcase remained intact. All six cylinders remained attached to the engine and displayed impact damage signatures with the left side cylinders sustaining more damage than the right. The induction and exhaust systems both displayed impact damage signatures, but there were no signs of exhaust or induction leaks noted. The fuel pump was impact damaged as were several of the fuel line fittings. The throttle and metering assembly remained attached to the engine and displayed impact damage signatures; both the throttle and mixture arms were broken. The fuel manifold valve remained attached to its installation point and displayedimpact damage signatures at the rear fitting. All of the fuel nozzles remained installed in their cylinders and there were no signs of fuel leaks near the nozzles. The 2 magnetos were undamaged and produced a spark at each ignition lead when manually rotated. The ignition harness displayed impact damage signatures to several of the left side cylinder ignition leads. All of the spark plugs remained installed in their cylinders and the top left spark plugs displayed impact damage signatures. The three-blade, constant speed propeller remained attached to the crankshaft and one of the blades was impact damaged. There were no pre-impact anomalies with the engine that would have precluded normal operation or production of rated horsepower. The gascolator top and bottom seals were comprised of rubber gaskets which were meshed to a wire screen by a glass cylinder. As assembled the glass cylinder was tightened between two caps which each contained the rubber gaskets and wire mesh. The gascolator was examined by an FAA inspector who reported that there were fuel stains on the top seal and the drain valve, indicative of a fuel leak at some point during the life of the unit (figure 2). Figure 2 – Gascolator installed on the airplane Sierra Hotel Aero, Inc. (SHA) holds the type certificate for the Navion. In May of 2007, SHA issued Navion Service Bulletin (SB) 106A - Fuel System - Inspection of the fuel system continued safe operation. The purpose of the SB was to require accomplishment of one time inspection of entire fuel system. This included from firewall aft for condition of all fuel lines installed including tip tanks, metal lines, fittings, hoses, vent system, vapor return, boost pump, and fuel strainer. The SB further states, inspect fuel strainer for evidence of fuel staining and leaking. Disassemble strainer and clean fuel screen. Inspect for damage and reassemble. Perform vacuum test of gascolator to include: connect hand operated vacuum pump and apply 24" of vacuum, verify bleed down does not exceed 4" over one minute, replace gaskets, fuel drain and/or gascolator as needed to ensure proper operation. The gascolator was subjected to postaccident testing as prescribed in the Navion SB No. 106 A. The outlet port was plugged using an appropriate AN plug fitting. The gascolator was filled with clean 100LL fuel. After the fuel was added, a significant amount of foreign debris was observed floating in the gascolator. A 7-inch aluminum line with AN fittings was attached to the inlet port and the other end to the gascolator. This line was previously leak checked with no anomalies found. The inspector applied 24 inches of vacuum pressure using a hand vacuum pump; the gascolator was tested and failed to hold the required 24 inches of vacuum pressure for any amount of time. During the test the gascolator was leaking from the top seal, bottom seal, and the drain valve. A review of the airplane maintenance logbooks revealed no record of compliance with theNavion SB No. 106 A, and there was no mention of gascolator maintenance from December 2006 to July 2017.