Dinsmore, CA, USA
N4474H
MOONEY M20J
A witness who was near the departure airport reported observing the airplane circle the area, land on the runway, and stop at the midpoint of the runway. At that time, three people disembarked from the airplane, one of whom walked around the airplane. All three people then boarded the airplane, and the airplane taxied toward the approach end of the runway. The witness observed the airplane take off and stated that the airplane appeared to have rotated just short of the displaced runway threshold. The witness stated that the airplane “barely cleared the fence” and that the rotation was not smooth. Subsequently, the airplane impacted trees just beyond the departure end of the runway, where a postimpact fire ensued. Postaccident examination of the engine revealed that the intake camlobes were worn and exhibited a rounded (instead of an elliptical) shape. The corresponding tappets for the intake cam lobes were galled. The alteration of the camlobe profile will in turn alter the amount and duration of the intake valves opening, thus negatively affecting power output. As a result, takeoff and climb performance would be directly affected. Although the extent of the degradation to the accident engine's power output could not be determined from the available evidence, the degradation was likely sufficient to cause a partial loss of engine power.
HISTORY OF FLIGHTOn July 15, 2021, at 1154 Pacific daylight time, a Mooney M20J airplane, N4474H, was destroyed when it was involved in an accident near Dinsmore Airport (D63), Dinsmore, California. The pilot, pilot rated passenger, and two other passengers were fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight. A witness, who was located 0.25 miles east of the departure end of runway 9 at the airport, observed the accident airplane circling the area twice before landing on runway 27. (The witness reported that the wind was from the west.) The witness then observed the airplane travel down the runway before making a complete stop at the midpoint of the runway, at which time three people disembarked, one of whom walked around the airplane. All three people then boarded the airplane, and the airplane taxied toward runway 9. The witness observed the airplane accelerate down the runway and stated that the airplane appeared to have rotated just short of the displaced runway threshold. The witness thought that the airplane “barely cleared the fence” and that the rotation was not smooth because the pilot had suddenly “jerked” the nose of the airplane. The airplane subsequently impacted trees and then the ground about 1,600 ft from the departure end of runway 9. Two security cameras, both of which were located about 300 ft east of the departure end of runway 9 (see figure 1), captured the accident airplane during the takeoff initial climb (see figure 2 for the view from one of the cameras). Figure 1. Camera and wreckage locations. Figure 2.: Security camera image showing the accident airplane at the departure end of runway 9 during takeoff initial climb. AIRCRAFT INFORMATIONThe airplane’s weight and balance records were not located. The Mooney M20J Pilot’s Operating Handbook contained a maximum performance takeoff distance chart. The chart showed that, at a takeoff weight of 2,740 pounds, a flap setting of 15°, a fuel/air mixture that was leaned for smooth operation, a temperature of 10°C, and an altitude of 2,000 ft, the ground roll would be 1,022 ft, and 1,732 ft would be required for a 50-ft obstacle clearance. At an altitude of 4,000 ft, the ground roll would be 1,309 ft, and 2,175 ft would be required for a 50-ft obstacle clearance. The calculated climb performance for the published gross weight at a density altitude of 2,500 ft would have been about 900 ft per minute with the landing gear retracted, maximum engine power, 0° flaps, and a rich fuel/air mixture. AIRPORT INFORMATIONThe airplane’s weight and balance records were not located. The Mooney M20J Pilot’s Operating Handbook contained a maximum performance takeoff distance chart. The chart showed that, at a takeoff weight of 2,740 pounds, a flap setting of 15°, a fuel/air mixture that was leaned for smooth operation, a temperature of 10°C, and an altitude of 2,000 ft, the ground roll would be 1,022 ft, and 1,732 ft would be required for a 50-ft obstacle clearance. At an altitude of 4,000 ft, the ground roll would be 1,309 ft, and 2,175 ft would be required for a 50-ft obstacle clearance. The calculated climb performance for the published gross weight at a density altitude of 2,500 ft would have been about 900 ft per minute with the landing gear retracted, maximum engine power, 0° flaps, and a rich fuel/air mixture. WRECKAGE AND IMPACT INFORMATIONThe wreckage was located on a magnetic heading of 126°. Examination of the accident site revealed that the airplane’s right wing impacted a tall redwood tree. Upon impact, the right wing separated and fell onto the ground underneath the tree. The airplane came to rest inverted about 120 ft from the first point of impact on a magnetic heading of 170°. Postaccident examination of the airplane revealed that the engine remained attached to the airframe by the engine mount. The engine sustained thermal and impact damage. The crankshaft rotated freely in both directions. Thumb compression was obtained on all four cylinders. The intake valve rocker arms of each cylinder moved about 40% less compared with the exhaust rocker arms. Disassembly of the engine found no evidence of heat distress on the crankshaft and its attached connecting rods. The main bearings exhibited signs of significant wear. The main bearing saddles at each crankcase exhibited significant fretting signatures. The camshaft was intact. Each exhaust cam lobe exhibited an elliptical shape, and the corresponding tappet face remained undamaged and smooth. The intake cam lobes exhibited a worn and rounded shape. The corresponding tappets for the intake cam lobes were galled. An engine monitoring unit was recovered from the wreckage. The data were subsequently downloaded. The data showed that, about 3 minutes into the recording, the engine speed increased to about 2,150 rpm and then further increased moments later to about 2,700 rpm. The manifold pressure increased to 27 inches. The recording ended about 35 seconds later with a recorded engine speed of 2,685 rpm and a manifold pressure of 27.3 inches. Other engine parameters appeared to be nominal.
The airplane’s degraded engine performance due to wear to the intake cam lobes, which diminished the airplane’s takeoff and climb performance, resulting in a subsequent collision with trees.
Source: NTSB Aviation Accident Database
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