Accident Details
On August 23, 2019, about 0946 eastern daylight time, a Beech F33A, registration N80WH, sustained substantial damage when it was forced to land near Hobe Sound, Florida. The private pilot and two passengers were not injured. The flight was conducted under Title 14 Code of Federal Regulations Part 91 as a personal flight.
Pilot Report
During preflight inspection, the pilot reported no anomalies. After departing to view properties, while in cruise flight, the pilot heard a "tap, tap, tap, tap and a bang" and noted the engine oil pressure gauge read zero. The aircraft was below 1,000 ft mean sea level, and the pilot initiated a forced landing. He flew under powerlines and landed on the embankment next to a roadway, where the airplane slid until coming to rest. The right wing, right tip tank, and right elevator sustained substantial damage.
Aircraft and Maintenance History
According to the airframe maintenance logbook, the most recent annual inspection was completed on April 21, 2018, at a total time of 4,591.2 hours. The most recent 100-hour inspection was completed on May 17, 2019, at 4,670.6 hours; the oil and oil filter were replaced and the filter was cut open with no defects noted. The aircraft total time at the accident was 4,674.7 hours. The engine had accrued 1,139.1 hours since its overhaul on August 1, 2004.
Engine Examination
Examination of the engine revealed a crack in the crankcase near the aft section of the spine. All 12 through bolt torque values exceeded the manufacturer's recommended torque of 490 to 510 in-lbs. The outer crankcase mating surfaces showed evidence of an unapproved sealant material with no silk thread present. Significant fretting was observed around the Nos. 1 and 2 bearing support through bolt holes, with some fretting at the Nos. 3 and 4 bearing support mating surfaces. The No. 1 bearing support had minor lock tab elongation, while the No. 2 lock tab was completely worn away. The Nos. 1 and 2 bearings exhibited signatures consistent with bearing shift, with the No. 2 bearing showing the most movement; a large portion had extruded from its support. The crankshaft was fractured between the No. 2 main bearing journal and the No. 2 connecting rod journal. Both sides of the fracture surface displayed thermal discoloration and incipient signatures of lubrication distress.
Engine Assembly Manual Warning
The maintenance and overhaul manual for the IO-550-B engine specifies proper assembly procedures, including part numbers for approved sealant and grade silk thread. It provides a warning: "Do not apply any form of sealant to the crankcase cylinder deck, chamfer, cylinder mounting flange, cylinder base O-ring, cylinder fastener threads or crankcase main bearing bosses. The use of RTV, silicone, Gasket Maker or any other sealant on the areas listed above during engine assembly will cause a loss of cylinder deck stud or through-bolt torque. Subsequent loss of cylinder attachment load, loss of main bearing crush and/or fretting of the crankcase parting surfaces will occur. The result will be cylinder separation, main bearing movement, oil starvation and catastrophic engine failure. USE ONLY CLEAN 50 WEIGHT AVIATION ENGINE OIL ON SURFACES LISTED."