Incident Overview
On September 9, 2020, at 0935 eastern daylight time, a Mooney M20R airplane, registered as N120GX, was substantially damaged in an accident near Weston, Florida. The pilot and passenger were not injured. The flight was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
Pilot Report
According to the pilot, the airplane had 6.5 quarts of oil (8 quarts total capacity) and 65 gallons of fuel before departing Naples for Fort Lauderdale, Florida, a 35-minute flight. About 20 minutes into the flight, at 3,500 ft mean sea level, he heard a loud pop, the propeller sputtered, and the engine began losing power. Oil pressure dropped from 58–60 psi to 0 psi, while other engine gauges remained normal except for a larger than normal battery draw. About 30 seconds later, part of the engine exited through the top of the engine cowling, and the engine and propeller stopped completely. The pilot executed a successful forced landing onto the right shoulder of an interstate highway. As the pilot and passenger prepared to exit, a truck struck the airplane's left wing from behind, spinning the airplane 180°.
Damage Assessment
A Federal Aviation Administration inspector examined the airplane at the accident site. Substantial damage included the left aileron, left wing trailing edge forward of the aileron, and inboard trailing edges of both elevators. A hole was found in the top left side of the engine cowling and in the engine case near the base of the No. 6 cylinder. Metal debris—including a damaged connecting rod, its separated cap, a piston wristpin, a valve lifter, and crankcase fragments—was found in the oil pan.
Engine Examination
Discoloration and thermal damage were observed on one crankshaft main bearing, one crankshaft connecting rod journal, and two connecting rods at their crankshaft ends. These findings were consistent with a lack of lubrication. No anomalies were found with the engine oil pump, and no blocked oil passages existed in the crankshaft.
Oil Consumption History
The pilot/owner reported that the day before the accident, he completed four flights over four days totaling about 16 hours. Over the last two flights (about 7.25 hours), the engine used about 3.5 quarts of oil (approximately 1 quart every 2.07 hours). After adding 2 quarts post-trip, bringing the level to 6.5 quarts, he noted oil consumption seemed high. He had added oil before two other legs, with the lowest observed level at just below 6 quarts. He recalled additions from memory without a written log. No oil leaks were observed. The accident flight was intended to get an oil change, and he planned to ask the maintainer to assess the consumption.
Flight Data Analysis
The airplane's electronic displays recorded flight data. Review of 34 previous flights showed typical cruise oil pressure between 60 and 65 psi, consistent and stable. Beginning six days before the accident, oil pressure deviated. On the third and second previous flights, oil pressure began decreasing about halfway through without changes in oil temperature or rpm and exhibited high-frequency fluctuations. The pressure dropped 15–20 psi over about 90 minutes to around 45 psi. On the flight before the accident, oil pressure never reached typical levels, decreasing throughout, entering the yellow range (10–30 psi) about one-third into the flight and briefly touching the lower red range (<10 psi) twice. During the accident flight, oil pressure was relatively typical but decreased about 7–8 psi in the three minutes before power loss.
Engine Instruments
Engine indications were displayed on the multifunction display (MFD). The MFD pilot's guide indicated that when unsafe operating conditions occur, corresponding readouts flash to indicate cautions and warnings. It did not specify if the oil pressure indicator would flash in the yellow range. The airplane had no secondary oil pressure gauge.
Maintenance History
The engine was manufactured in May 2006, installed when the airplane was built, and had 1,166 total hours. It had not been overhauled; the manufacturer recommended overhaul at 2,000 hours or 12 years, whichever came first. The most recent oil change was 38 flight hours before the accident (July 10, 2020), with no anomalies noted on the oil filter. The most recent annual inspection was 81 flight hours earlier (May 29, 2020), with no anomalies in the logbook entry. However, a supplemental Mooney inspection guide noted "Dirty Oil – gunk in filter" and "oil was awfully dirty, filter was not clean, gunk like substance in filter folds." Cylinder compression did not vary significantly except cylinder No. 2, which increased by 20 psi. Review of the last 10 oil changes showed intervals of 21 to 46 hours; no other anomalies were noted, though five records did not specify if the oil filter was examined.