Accident Sequence
On February 12, 2023, about 0958 central standard time, a Mooney Aircraft Corporation M20K Encore airplane, N304MA, sustained substantial damage when it was involved in an accident near Lakeway, Texas. The pilot sustained no injury. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal cross-country flight.
The pilot reported that he had recently purchased the airplane and was relocating it to his home base at Outlaw Field Airport (CKV), Clarksville, Tennessee. During the preflight inspection, the pilot did not observe any anomalies. He reported that the airplane had 57 gallons of fuel onboard at takeoff and the engine oil was at a sufficient level for flight operations.
A review of ADS-B data showed that the airplane departed from Kestrel Airpark (1T7), Spring Branch, Texas, and traveled to the northeast. The pilot reported that while in flight, the engine had a low manifold pressure reading and then the engine sustained a total loss of power. The ADS-B data showed that the airplane performed a 180° turn as it approached the Colorado River just to the north of Bee Cave, Texas. The pilot then maneuvered the airplane north toward the Lakeway Airpark (3R9), Lakeway, Texas.
Unable to make the airport, the pilot performed a forced landing to a golf course just to the north of 3R9. During the forced landing, the airplane impacted trees and a wood fence, and came to rest upright near a diesel generator. The pilot was able to egress from the airplane without further incident. The airplane sustained substantial damage to the fuselage and to both wings.
Examination Findings
A Federal Aviation Administration (FAA) inspector responded to the accident site. A large amount of engine oil was observed trailing rearward on the underside of the fuselage. The engine oil level was checked at the accident site and oil was not observed on the dipstick.
Examination of the airframe revealed flight control continuity. Both wing fuel tanks were found breached and no anomalies were noted with the airframe.
Examination of the engine revealed a hole in the corner of the No. 6 piston; however, the No. 6 cylinder was intact. The No. 6 piston had eroded crown material and a darkened periphery. The engine case was found intact. The top spark plugs from the Nos. 3, 5, and 6 cylinders and the bottom spark plugs from the Nos. 3 and 5 cylinders were found in a “worn out - normal condition.” The right magneto timing was found at 22°; according to the engine manufacturer, it is supposed to be at 20°. The left magneto timing was found at 15°, rather than 20°. The oil breather tube was found intact and the slot was not blocked. Engine oil was found splattered in and around the oil breather tube area, including traveling rearward on the area underneath the oil breather tube. No anomalies were noted with the turbocharger system or the propeller.
A review of data obtained from a J.P. Instruments EDM-700 unit onboard the airplane at the time of the accident showed an excessively high No. 6 cylinder head temperature reading about 17 minutes before the unit stopped recording data.
Background and Maintenance
Before purchasing the airplane, the pilot had an inspection performed by a mechanic. One of the findings on the undated inspection list stated that, “spark plugs are worn past limits.” Additionally, all cylinders were borescoped and the cylinders were listed as, “all appear normal.” The pilot reported that there were no indications that the magneto timing was checked during the prebuy inspection. The pilot further reported that the airplane had been run with a lean mixture in the past. A review of the engine maintenance records showed that the most recent time the spark plugs were cleaned and gapped, and the magneto timing was checked was during a 100-hour inspection on October 8, 2022, at 2,732.4 hours.
The FAA has published the Pilot’s Handbook of Aeronautical Knowledge FAA-H-8083-25C. This document discusses detonation and preignition, their causes, and effects. Continental Motors has published Mandatory Service Bullet MSB94-8D Magneto to Engine Timing on February 17, 2010, which discusses the importance of maintaining correct magneto timing and states that incorrect timing can lead to detonation, preignition, and internal engine damage or failure.