N2073K

On December 21, 2023, about 1210 Pacific standard time, a Mooney M20J airplane, N2073K, was substantially damaged when it was involved in an accident near Carlin, Nevada. The pilot and the passenger sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The pilot reported that in preparation for a cross-country flight from Redding Municipal Airport (RDD), Redding, California, he topped off the airplane’s fuel tanks and departed with the intended destination of Glendale Municipal Airport (GEU), Glendale, Arizona. About 2 hours into the flight, the airplane climbed from 11,500 ft to 13,500 ft msl and the pilot configured the airplane’s trim, fuel mixture, and power to maintain cruise flight while operating with the fuel selector in the left tank position.

About 20 minutes later, the pilot heard what he referred to as a “loud clunk” sound from the engine, followed by strong vibrations and the smell of engine oil. The pilot turned on the fuel boost pump, moved the fuel selector to the right tank position, and made a left turn to the northwest while continuing to troubleshoot the anomaly; he declared an emergency with the Salt Lake City Center ARTCC controller. Moments later, the engine lost all power. The pilot attempted to restart the engine to no avail, selected the nearest suitable landing site, and made an off-airport, gear-up, forced landing in mountainous terrain. The airplane landed about 9 miles south of Carlin, Nevada, and sustained substantial damage to the outboard section of the right wing. The pilot did not recall the manifold pressure or engine rpm before the loss of power.

The single-drive dual magneto was found securely clamped at the mounting pad. The magneto impulse coupling was heard clicking near top dead center during rotation of the crankshaft. However, the magneto-to-engine timing could not be confirmed using a timing synchronizer box, which did not produce an expected audible tone to indicate that either of the magneto contact assemblies were open. The magneto did not produce spark at any of the ignition leads and was removed for further examination.

The magneto distributor housing was removed and neither of the contact assemblies was found to be functioning. The contacts did not appear burnt and the plastic cam follower foot was intact and showed no evidence of heat distress. There was no evidence of mechanical malfunction of the internal gears. The wiring within the magneto appeared normal. The magneto cap internal surfaces and wires remained free of oil residue or evidence of arcing.

The magneto drive was rotated by hand after supplying power and neither the left nor right contact assembly cam follower engaged the main breaker point frame bracket. After manually separating the main breaker point from the retard breaker point, the right magneto produced an audible tone and the green light illuminated; however, the left magneto did not.

Figure. Cam end view of magneto.

The magneto was shipped to the manufacturer for bench testing. The bench test revealed that the right magneto produced a spark at each of the four ignition leads. The left magneto did not produce a spark at any of the leads. The magneto distributor housing was removed for further examination and revealed that the right magneto cam follower was engaging the cam, allowing the contact assembly breaker points to open when the cam lobe lifted the cam follower, contact assembly frame bracket, and breaker point. However, the left magneto cam follower was not engaging the cam.

The engine manufacturer’s High Tension Magneto Service Support Manual (pages 9-15) provided instructions to adjust the assembly frame bracket for breaker point clearance. The instructions stated that the cam should be rotated so the high lobe(s) is (are) under the cam followers of the contact assemblies, that the left main contact should be adjusted to obtain a 0.016 inch (± 0.002) opening, and that the retard contacts should have 0.016 inch (± 0.004) clearance.

The contact assembly frame bracket was adjusted to increase the breaker point opening clearance and the magneto drive housing and the distributor housing were reassembled. A second bench test was conducted, and both the left and right magnetos produced electrical impulses to each of the designated ignition leads in firing order (1, 3, 4, 2). The left main contact opening clearance was not measured before or after the bench test.

A review of the airplane’s maintenance logs showed that during the last annual inspection, the magneto-to-engine timing was checked. However, a definitive magneto service history could not be determined.