Hager City, WI, USA
N61429
North American P-51C
The airplane collided with trees and terrain following a loss of engine power while maneuvering during an airshow. Witnesses reported hearing the pilot state that he had an engine malfunction as he was lining up for a low pass over the airport. They stated the propeller was turning, but the airplane was descending. The airplane passed under high tension power lines and collided with trees prior to coming to rest in the back yard of a residence. Examination of the engine revealed the upper vertical camshaft drive gear had backed off of the drive shaft. The camshaft gear fits on splines on the upper vertical drive shaft followed by a tab washer, a retainer washer, and a retaining nut. The retainer washer has two interior tabs that insert into smaller splines at the top of the shaft, which keep it from rotating. On the outer diameter surface, the retainer washer contains slots where tabs from the tab washer can be bent into place. A metallurgical examination of the gearbox cover, retaining nut, retaining washer, tab washer, and the camshaft drive gear revealed the components were installed in the correct order. The damage on the components indicates that the tabs on the tab washer were most likely not bent into place around the retaining washer and nut, allowing the nut to back off the shaft. It could not be determined if the nut had been properly torqued during its installation. The engine had been overhauled approximately 424 hours prior to the accident.
HISTORY OF FLIGHT On May 29, 2004, at 1410 central daylight time, a North American P-51C, N61429, operated by the American Airpower Heritage Flying Museum, collided with trees and terrain in Hager City, Wisconsin, following a loss of engine power while maneuvering during an airshow at the Red Wing Regional Airport (RGK), Red Wing, Minnesota. The pilot was fatally injured. The airplane received substantial damage. The 14 CFR Part 91 flight was operating in visual meteorological conditions without a flight plan. The airplane departed from RGK about 1330. The accident occurred during the Wings of Freedom Airshow. The airshow airboss reported the airplane was lining up for a west to east pass over the airport when he heard the pilot radio that he had an engine malfunction. He stated an individual radioed to the pilot to "turn on your boost pump" and another individual instructed the pilot to pull his propeller back. A witness reported seeing the airplane make a low pass over the runway followed by a turn to the north to line back up with the runway heading east. This witness reported the airplane appeared to be traveling slower then it was during the previous low pass. He stated the propeller was still turning, but the airplane was descending with the landing gear retracted. He reported he then lost sight of the airplane behind the trees. Another witness reported seeing the airplane approach the airport heading east. This witness reported the airplane descended and passed under wires prior to contacting the tress. PERSONNEL INFORMATION The pilot held an airline transport pilot certificate with an airplane multi-engine land rating. He also held a commercial pilot certificate with an airplane single-engine land rating. In addition, the pilot held a flight engineer certificate with a turbojet powered rating. The pilot held a second class airmen medical certificate that was issued on May 8, 2003. The medical certificate contained the limitation that the holder shall posses glasses for near and intermediate vision. The pilot reported having 3,000 hours of civilian flight time at the time of his last airmen medical examination. According to records provided by the American Airpower Heritage Flying Museum, the pilot began flying the accident airplane in November 2002. Since that time, the pilot had accumulated 124.9 hours of flight time in the airplane. AIRCRAFT INFORMATION According to the aircraft logbooks, the last annual inspection was performed on March 28, 2004. The aircraft total time listed in the aircraft logbook at the time of the inspection was 2,832.1 hours. According to a flight log, the airplane had been flown approximately 15 hours between the date of inspection and May 24, 2004. The aircraft engine, a Rolls Royce V1650-7, s/n V301757, was overhauled and installed on N61429, on May 10, 2001. The aircraft total time when the engine was installed was 2,423 hours, or about 424 hours prior to the accident. METEOROLOGICAL INFORMATION The weather reporting station located at the departure airport listed the conditions at 1415 as: Wind - 120 degrees at 19 knots gusting to 25 knots; Visibility - 10 statute miles; Sky Condition - 1,000 foot overcast; Temperature - 14 degrees Celsius; Dew Point - 11 degrees Celsius; Altimeter Setting - 29.77 inches of Mercury. WRECKAGE AND IMPACT INFORMATION Inspectors from the Federal Aviation Administration (FAA), Minneapolis, Minnesota, Flight Standards District Office (FSDO), conducted an on-scene examination of the accident site. The accident site was located in the back yard of a residence at W7496 140th Avenue, Hager City, Wisconsin. The airplane impacted trees prior to coming to rest on its right side. Pieces of the left wing separated from the airplane as it traveled through the trees. The right wing was separated from the fuselage and was located next to the fuselage. The right horizontal stabilizer was crushed, and the vertical stabilizer was wrinkled. The landing gear was in the retracted position, and the propeller was separated from the engine. MEDICAL AND PATHOLOGICAL INFORMATION An autopsy was conducted on the pilot at the Ramsey County Medical Examiner's Office on May 30, 2004. Toxicological tests were performed by the FAA, Civil Aeromedical Institute in Oklahoma City, Oklahoma. A Final Forensic Toxicology Fatal Accident Report listed the following findings: 0.494 (ug/ml, ug/g) Morphine detected in liver 1.14 (ug/ml, ug/g) Morphine detected in kidney Lidocane detected in liver Lidocane detected in kidney The pilot survived for a short period of time following the accident. The above listed substances were administered as part of his medical treatment. TEST AND RESEARCH The engine was disassembled under the supervision of an FAA inspector. The inspector reported the upper vertical camshaft drive gear had backed off of the drive shaft. The camshaft gear fits on splines on the upper vertical drive shaft followed by a tab washer, a retainer washer, and a retaining nut. The retainer washer has two interior tabs that insert into smaller splines at the top of the shaft, which keep it from rotating. On the outer diameter surface the retainer washer contains 10 slots where tabs from the tab washer can be bent into place. The tab washer that is below the retainer washer also has 10 tabs, while the retainer nut has 8 slots. After the retainer nut is torqued down only two of the tabs on the tab washer/retainer washer line up with the slots on the retaining nut. One or two are then bent over the retainer washer and retainer nut to secure the assembly in place and keep the nut from backing out while in service. The gearbox cover, retaining nut, retaining washer, tab washer, and the camshaft drive gear from the accident airplane were sent to the National Transportation Safety Board metallurgical laboratory in Washington, DC, for examination. The examination revealed: Gearbox Cover: The rub area outlined [inside the gearbox cover] is larger than the diameter of the gear, consistent with the components rotating in a non-concentric manner at the point of contact. At the fraction location on the oil tube significant rubbing marks were observed, consistent with damage from the nut rubbing in that area. Retaining Nut: Visual examination of the retaining nut revealed fretting damage on the entire lower face that contacts the retaining washer and rubbing damage toward the outer diameter (OD) on the top face. At the top OD surface the gear teeth were rounded and material was rolled over into the tab slots. On the lower face the markings "OFF 602245" with a skinny arrow was observed. Retaining Washer: Visual examination of the retaining washer showed that 4 to the 10 teeth on the OD were fractured off. The two locking tabs on the ID [inner diameter] were intact, but both edges of the locking tabs were deformed from contact with the shaft splines. Shadowed inverted marking "OFF" and a partial skinny arrow, consistent with transferred markings from the lower side of the retaining nut, were observed on the face of the retaining washer. When the retaining washer is placed on the retaining nut only two opposing slots align so that only one or two of the tab washers can be bent into the retaining nut slots. Examination of the fracture surfaces of the retaining washer tabs revealed that they all showed flat features with arrest marks and ratchet marks on both sides of the teeth consistent with reverse bending fatigue. Tab Washer: Three pieces of the tab washer were recovered and submitted for examination. The first section extended between arbitrarily number tabs 1 and 7. On this piece tabs 1, 2, and 7 were fractured off. Based on fracture surface matching, the recovered broken tab piece (second piece) was tab 1. The third piece was a section extending between tabs 8 and 10 with all tabs intact. Visual examination of tab number 1 showed that it was very straight, relatively undamaged, and had a slight bend of about 20 degrees from flat at the fracture surface neat the ID. Examination of the fracture surface showed that there were ratchet marks starting from the top (nut) side in the inside of the bend in the tab, and that a large portion of the fracture surface was very flat and had a thumbnail shape that was darker in color consistent with fatigue. The fatigue region consumed approximately 60 % of the cross-sectional area. The fracture surface of tab number 2 showed severe deformation and extensive damage with features consistent with overstress. Tab number 7 showed a flat fracture surface, ratchet marks, and a thumbnail pattern consistent with fatigue initiating from the top side. Camshaft Drive Gear: Visual examination of the camshaft drive gear showed that some of the gear teeth were rubbed with sections fractured off on the lower side of the teeth. On the top face of the gear near the ID spline, fretting and galling damage was observed. The damaged area matched the outline of the retainer washer after it lost the four teeth. The overhaul manual stated that the camshaft drive gear hardware should be assembled, and the nut should be torqued down, but the tabs should not be bent at this point. The inclined gears should then be installed, shimmed, and assembled. When all the spacing and clearances are checked between the three gears, then the tabs of all three gears should be bent over at the same time. ADDITIONAL INFORMATION The FAA was a party to the investigation.
The improper installation of the camshaft drive gear assembly which resulted in the retaining nut backing off allowing the drive gear to move up the shaft. A factor associated with the accident was the low altitude at which the power loss occurred and the trees which the airplane contacted during the forced landing.
Source: NTSB Aviation Accident Database
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