History of Flight
On August 16, 2012, about 0839 eastern daylight time, an experimental, amateur-built Jabiru J230, registration N365R, sustained substantial damage during a ditching in Gull Lake, near Otter Lake, New York. The aircraft experienced a total loss of engine power and separation of the propeller. The public use flight was operated by Patriot Technologies LLC under contract with the Department of Defense, U.S. Air Force. The airline transport pilot and one additional crew member were not injured. Visual meteorological conditions prevailed, and no flight plan was filed for the flight, which departed Burlington International Airport (BTV), Burlington, Vermont, about 0800, destined for Griffiss International Airport (RME), Rome, New York.
According to the operator, the purpose of the flight was to provide aerial support for a U.S. Air Force training exercise. At the time of the accident, the flight was receiving VFR flight following from the New York Air Route Traffic Control Center (ARTCC).
The pilot reported that after departing BTV, he headed westbound and climbed to 6,500 feet above mean sea level. Approximately 45 minutes into the flight, the engine began to run roughly "like it was developing carburetor ice," so the pilot applied carburetor heat. The engine continued to run rough and began to "cough" as if starved for fuel, prompting the pilot to ensure both fuel valves were open and turn on the electric fuel boost pump. The pilot then assessed that the engine might stop, and called for the high altitude engine failure checklist. Before he and his crewmember began the checklist, the propeller separated from the engine, struck the right side of the cowling and the right lift strut, and fell away. The pilot declared an emergency with ARTCC, evaluated landing sites, and elected to ditch in a nearby lake. After ditching, the airplane came to rest on the lake surface with the cabin halfway submerged. Both crewmembers egressed, swam to shore, and were later picked up by helicopter. The airplane later sank to the bottom of the lake.
Personnel Information
According to FAA and pilot records, the airline transport pilot held an airline transport pilot certificate with ratings for airplane multi-engine land, commercial privileges for airplane single-engine land, and type ratings in the BE-300 and C-295. He also held a flight instructor certificate with ratings for airplane multi-engine and instrument airplane. His most recent FAA second-class medical certificate was issued on June 4, 2012. He reported 3,147 hours of total flight experience, 42 of which were in the airplane make and model.
The crew member held a commercial pilot certificate with ratings for airplane multi-engine land limited to center thrust, instrument airplane, and private privileges for airplane single-engine land. At the time of the accident, he did not possess a valid FAA medical certificate. He reported 2,350 hours of total flight experience.
Aircraft Information
According to FAA and airplane maintenance records, the airplane was manufactured in 2005. Its most recent conditional inspection was completed on February 27, 2012. At the time of the accident, the airplane had accrued 915.2 total hours of operation. The engine had accrued 531.2 total hours of operation.
Meteorological Information
The recorded weather at RME, approximately 25 nautical miles southwest of the accident site, at 0853, included calm winds, visibility 10 miles, overcast sky at 1,200 feet, temperature 19°C, dew point 16°C, and an altimeter setting of 29.98 inches of mercury.
Wreckage and Impact Information
Four days after the ditching, the airplane was recovered from the lake. Examination revealed that the airplane was substantially damaged due to water immersion. The entire propeller assembly, including the propeller spinner and propeller flange extension, had separated from the forward portion of the engine crankshaft. Despite a search, the separated components of the propeller assembly were not found.
Tests and Research
Maintenance records review indicated that the valves and valve seats had been reground/recut at 204 hours total engine operating time. Sparkplugs were replaced at 451.6 hours. On August 5, 2012, approximately 11 days prior to the accident, at 510.8 hours, the exhaust gas temperature (EGT) probes were inspected.
Engine examination by Jabiru Pacific LLC revealed that the capscrews holding the propeller flange extension onto the engine crankshaft appeared to have sheared off. The top of the engine case under the starter near the No. 6 cylinder was disfigured. Attempts to rotate the drive train in both directions were unsuccessful, indicating the engine was seized internally. Examination of cylinders No. 1 through No. 5 showed no preimpact anomalies, but the No. 6 cylinder exhibited significant damage: the exhaust valve and valve seat were missing, the piston was lying in the bottom of the cylinder, the wrist pin was broken into two pieces, and the connecting rod was bent almost in half and wedged between the crankshaft and the top of the engine case. The oil pan contained shattered portions of the No. 6 piston, piston rings, and the exhaust valve head. Parts of the exhaust valve seat were found in the muffler.
Materials laboratory examination confirmed the No. 6 cylinder exhaust valve seat had dislodged and fractured into multiple fragments with overstress features. Lead-like deposits were found on the No. 6 cylinder exhaust and confirmed as lead via energy dispersive spectroscopy (EDS). Lead deposits were also present on other cylinders and pistons. The No. 6 rocker arm shaft and exhaust valve rocker arm bushing exhibited abrasive wear. The exhaust valve spring free height was within limits. Valve assembly recess sidewalls showed deformation and wear consistent with impingement by the valve spring, also observed on No. 2 and No. 4 cylinders but not on No. 1, 3, or 5.
The No. 6 cylinder exhaust valve head had fractured from the stem near the transition from head radius to stem. The fracture surface was flat and perpendicular to the stem axis, with multiple ratchet marks consistent with fatigue crack initiation and propagation from multiple sites. SEM examination revealed dark thumbnail-shaped regions at crack initiation sites, with lead deposits except where material spalled. EDS within thumbnail regions showed higher oxygen content than outside. Outside thumbnails, the spectrum indicated iron, chromium, manganese, and nickel. Spalled material on the stem surface near the fracture had high oxygen. A dark grey coating near the spalled region had high oxygen and chromium. Outside spalled area, high lead concentration.
Crankshaft examination showed the propeller flange had six threaded bolt holes with fractured capscrew shanks and three smooth bored holes with no evidence of installation. Capscrew fracture faces had smooth appearance with smear marks oriented in rotation direction; some were deformed in that direction, consistent with overstress shear fracture. Each shank had approximately 0.4 inch of thread engagement and threads coated with thread locking compound per Jabiru Service Bulletin JSB 022-1. Hardness testing showed all capscrews within specified limits for Unbrako 1960 type (38-43 HRC).
Jabiru Aircraft reported approximately eight previous in-service failures of exhaust valves, noting intolerance to temperatures over approximately 750°C, with heat stress as the most common issue. They also reported approximately eight instances of propeller flange attachment separation due to various causes including incorrect capscrew length, non-approved propellers, high time without replacement, improper torque, lack of thread-retaining compound, and fatigue from insufficient clamping force due to trapped thread locking compound. Jabiru issued service bulletins JSB 014 and JSB 022 and changed new engine configuration to a longer flange and added three 8mm dowels between crankshaft and propeller flange starting in July 2011 with engine serial number 33A2446. All 2,445 engines prior had no dowels.
Additional Information
In response to the accident, Patriot Technologies Group LLC advised the NTSB on September 18, 2012, that they would install new propeller flange hubs and dowel pins to airplanes in their fleet not equipped with propeller dowel pins. Jabiru Aircraft advised on October 1, 2013, that they would expand guidance on extended running at low rpm/high altitude in Service Letter JSL 007-4 to help preclude lead buildup. On October 11, 2013, Jabiru advised that the next revision of the Engine Overhaul Manual would include directions on retaining compound application, excess compound avoidance, and a recommendation for owners to upgrade to propeller flange dowels during overhaul.