Accident Overview
On December 9, 2018, at approximately 1215 eastern standard time, a Mooney M20K (registration N5756W) was substantially damaged during a forced landing near Paramus, New Jersey. The private pilot and one passenger sustained minor injuries, while two other passengers were uninjured. The cross-country flight originated from Lincoln Park Airport (N07) in Lincoln Park, New Jersey, around 1200, with an intended destination of Hudson Valley Regional Airport (POU) in Poughkeepsie, New York. Visual meteorological conditions prevailed, and no flight plan was filed. The flight was conducted under 14 CFR Part 91.
Accident Sequence
According to the pilot, while cruising, he observed an increase in cylinder head temperature on two cylinders. Attempts to reduce the temperature were unsuccessful, and he soon heard an explosion, followed by noticing a hole in the engine cowling. The pilot executed a forced landing onto a golf course. During the landing roll, the airplane impacted a berm, became airborne again, and struck the ground. The landing gear collapsed, and the right wing sustained substantial damage.
Aircraft and Engine Information
The Mooney M20K was manufactured in 1984 and registered to the pilot in November 2017. It was equipped with a Continental Motors Inc. TSIO-360-LB1, 210-horsepower engine. According to the airframe maintenance logbook, the most recent annual inspection was performed on August 15, 2018, at a total time of 2,401.3 hours. The engine logbook indicated an overhaul on January 11, 2016, at 2,185 hours, and at the time of the accident, the Hobbs meter read 2,440.8 hours.
Engine Examination Findings
The engine was examined under NTSB supervision at the manufacturer's facility. The engine case was breached over the No. 2 cylinder. The oil sump and oil filter contained metallic debris. Scoring was observed inside the oil pump housing. Upon splitting the crankcase, the No. 1 connecting rod was found separated from the crankshaft, and the No. 1 and No. 2 connecting rods exhibited thermal discoloration. Remnants of silk thread were discovered around the through-bolt holes on the main bearing saddles. Break-away torque measurements showed that 8 of the 12 through-bolt torque values were below the manufacturer's recommended specifications. Specifically, the through-bolts associated with the No. 2 and No. 3 main bearings measured between 172 and 395 inch-pounds, well below the specified 590 to 610 inch-pounds. The No. 2 main bearing saddles had impingement damage, and the No. 2 bearing was partially rotated clockwise, blocking the oil passage to the connecting rod bearings.
Maintenance Guidance
The engine manufacturer published a Service Information Letter (SIL) on sealants and lubricants, initially released in 1999 and revised in 2014. This guidance instructed that during crankcase reassembly, a continuous silk thread should be applied on the 2-4-6 case half but explicitly prohibited its placement on the No. 2 main bearing saddle. Additionally, the Continental Aircraft Engine Maintenance Manual (dated April 2016) warned against applying sealants to specific areas, stating that improper application could lead to loss of main bearing crush, oil starvation, and catastrophic engine failure.