CEN17IA233

The pilot and a flight instructor planned to conduct an inflight calibration of an angle of attack indicator. Following a zero g-force maneuver, engine oil pressure decreased to 3 psi and engine speed increased to 3,140 rpm. Immediately after the engine overspeed, a total loss of power occurred. The pilot performed a forced landing to the departure airport without further incident. Examination of the engine revealed one of the two rear crankshaft counterweights (6th order) separated from the crankshaft, with a 6th order counterweight connecting pin lodged in the crankcase between cylinder Nos. 4 and 6. An impression in the No. 1 connecting rod matched the shape of a 6th order counterweight connecting pin. The oil sump contained significant debris, including four counterweight pin retaining snap rings, four counterweight pin retainer plates, and two 6th order counterweight connecting pins. Based on the examination, the lack of oil pressure and subsequent engine rpm overspeed/surge likely caused the separation of the crankshaft counterweight and engine failure.

HISTORY OF FLIGHT On June 1, 2017, at 1830 eastern daylight time, a Lancair IV-P airplane, N366TF, lost engine power and conducted a forced landing at the Oswego County Airport (FZY), Fulton, New York. The pilot and flight instructor were not injured and the airplane sustained minor damage. The airplane was registered to and operated by MS Rochelle LLC under the provisions of 14 Code of Federal Regulations Part 91 as a personal flight. Day visual meteorological conditions prevailed for the local flight, which departed from FZY at 1819 The purpose of the flight was to calibrate an Advanced Flight Systems Advanced Pro 3 angle of attack system, which included a series of zero g-force maneuvers. According to the flight instructor, during the first maneuver, he and the pilot noticed an engine overspeed, as well as a noticeable "bang" and a total loss of engine power. The pilot performed a forced landing at FZY without further incident. During the descent and landing, the propeller continued to windmill. According to data downloaded from the onboard Electronics International MVP-50 engine monitor, engine start occurred at 1806. A normal engine runup occurred at 1816, including magneto and propeller governor checks. Takeoff with full engine power occurred at 1819 and the airplane climbed normally to 12,000 ft msl. At 1829:29, the zero g-force maneuver occurred. Oil pressure indications, which had been normal until this time, decreased to 3 psi by 1829:32, followed by an engine overspeed of 3,140 rpm at 1829:34. From 1829:34 to 1830:10, engine rpm indications varied from zero to 2,700 rpm, and oil pressure indications varied from zero to 50 psi. At 18:29:38, the alternator charge indication dropped to zero. AIRCRAFT INFORMATION The composite airplane was constructed from a kit with components manufactured by Lancair International, Inc. The airplane was equipped with a Continental Motors TSIO-550E engine (s/n 803138), an MT Propeller USA MTV-14-D constant-speed four-blade wood propeller (non-counterweighted), and a McCauley C290D3-K/T43 propeller governor. According to the engine's type certificate data sheet, maximum engine rpm was 2,700 rpm. The oil sump capacity was 12 quarts, with 6.5 quarts usable at a 14.5 degrees nose down attitude. According to engine logbooks, a teardown inspection occurred on December 18, 2008, due to a propeller strike. On October 15, 2012, Barrett Precision Engines Inc. overhauled the engine, which included documented compliance with Continental Motors Service Bulletin 00-3, Counterweight Installation. On February 1, 2017, an entry was recorded to correct a rough running engine and a rising No. 3 cylinder exhaust gas temperature; which maintenance attributed to incorrect timing. On April 7, 2017, the No. 3 cylinder was replaced, due to a fractured bolt on the intake rocker shaft. ENGINE EXAMINATION Examination of the engine revealed the crankcase was breached in several places and the camshaft drive gear was displaced awayfrom the crankshaft drive gear. Extensive internal damage was noted to the interior of the crankcase and cylinder skirts, due to connecting rod contact. Both magnetos were dislodged from their respective mounts. One of the two rear crankshaft counterweights (6th order) was separated from the crankshaft, and the Nos. 1 and 4 connecting rods were fractured. The oil tube from the sump to the oil pump was compromised and thermal discoloration and oil starvation distress were noted on the Nos 2, 3, 4, and 6 connecting rods and bearings. The oil sump contained significant metal fragments, including four counterweight pin retaining snap rings, four counterweight pin retainer plates and two 6th order counterweight connecting pins. After separating the engine case, a 6th order counterweight connecting pin was found lodged in the crankcase between cylinders Nos. 4 and 6 and an impression in the No. 1 connecting rod matched the shape of a 6th order counterweight connecting pin. ADDITIONAL INFORMATION On November 15, 2015, a Lancair IV-P accident occurred that involved the same model engine, propeller, and propeller governor as this incident. The sequence of events for the accident (NTSB# CEN16LA043) involved a practice emergency descent with a 0.5 g-force load factor, which led to an engine oil pressure drop, engine overspeed, and total loss of power. The investigation concluded that a duel magneto failure occurred due to an engine overspeed/surge inducing shock loads on the gear train. During this investigation, several Lancair pilots who had competed in the Reno Air Races stated that low G maneuvering would often result in a transient drop in engine oil pressure and an engine surge and/or overspeed. According to the Federal Aviation Administration (FAA) small airplane standards staff, an angle of attack system calibration procedure which requires zero g-force flight is not approved for installation on certified aircraft.