N141PBLancair LC42-550FG

On June 20, 2024, about 1031 Pacific daylight time, a Lancair LC42-550FG (Columbia 350), N141PB, was substantially damaged when it was involved in an accident near Humboldt Bay, California. The pilot was not injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

The airplane had just departed Murray Field Airport (EKA), Eureka, California, after receiving an instrument flight rules clearance to Napa County Airport (APC), Napa, California. During the initial climb, the airplane passed through a cloud layer, after which it broke out into visual meteorological conditions at an altitude of about 1,500 ft mean sea level (msl). As the airplane climbed through 2,300 ft msl, the pilot established communications with the Seattle Air Route Traffic Control Center. About one minute later, he noticed a change in engine noise, with an accompanying vibration. The engine monitor indicated the cylinder head temperature for cylinder No. 6 was rising, and a short time later the engine lost all power and appeared to seize.

The pilot declared an emergency and was provided vectors back to EKA. While the airplane was turning toward the airport, it descended into the cloud layer. The airplane broke out into visual conditions about 700 ft msl over coastal marshland. The pilot maneuvered the airplane toward the flattest looking area, and on touchdown the airplane nosed over. The airplane sustained substantial damage to the vertical stabilizer and rudder, along with the forward cabin roof.

Postaccident examination of the engine revealed that the engine had lost most of its oil in flight, with only 1 quart of oil remained in the sump (its capacity was 8 quarts). The entire belly of the airplane was coated in oil and, within the engine compartment, the lower inner surface of the lower cowling, along with the left side of the engine, was coated in a sheen of oil.

Examination of the rocker covers revealed that the gasket for the exhaust rocker for cylinder No. 2 (on the left aft side of the engine) was misaligned in its lower right corner, such that a gap between the rocker cover and cylinder head was present (figure 1).

The cover was removed, and a dark stain was present on the face of the gasket mating surface, which mirrored the misalignment of the gasket (figure 2).

Figure 1. Misaligned gasket (left); gap in the gasket seal (right).

Figure 2. Witness marks showing pre-existing misaligned gasket on rocker (left) and cover (right).

The oil cooler and all oil lines were intact and showed no evidence of leaks. Both the oil sump drain plug and the quick drain plug were intact and locked. The outer surface of the oil filter, which was mounted behind the aft engine baffle and forward of the firewall, was clean, dry, and firmly attached to its adapter. The oil filter element was covered in fine metallic particles. Although the engine crankshaft could be rotated by hand at the propeller hub, its motion felt stiff, with more resistance than typical.

Other than the rocker cover gasket misalignment, the engine examination revealed no evidence of any preimpact mechanical malfunctions or failures that would have precluded normal operation.

The most recent airplane maintenance was completed about 20 flight hours before the accident, on September 17, 2023. At that time, an annual inspection was performed, along with replacement of all six engine cylinder and valve assemblies. The logbook entry stated that ground operation checks were performed following the maintenance, and no leaks were noted.

Continental Aerospace Technologies issued Service Information Letter SIL21-04B in August 2021, which was applicable to the accident engine. The letter provided instructions for installing an updated 100% silicone rocker cover gasket (part number 668893) in place of previous fiber and combination fiber/silicone bead gaskets. The letter stated that the new gasket “provides a more flexible seal than the previous gasket, when properly installed.”

The letter included a caution that failure to adequately clean the rocker and rocker cover flanges will cause an oil leak. It also specified reduced torque values for attaching the cover fasteners than those used for the fiber-based gaskets and stated that if the lower values were not used, the gasket and cover would be damaged.

The newer silicone gasket had been installed in the engine, and both it and the rocker cover were undamaged. Review of the Federal Aviation Administration’s service difficulty reporting system database did not find any reports of failures of the newer silicone gasket.