On April 28, 2024, about 1815 Pacific daylight time, a Bellanca 17-31ATC, N8800V, was substantially damaged when it was involved in an accident near El Cajon, California. The pilot sustained minor injuries. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.
The pilot reported that an annual inspection had just been completed on the airplane and the intent of the accident flight was to conduct a test flight in the local area to ensure everything was functioning properly. He conducted a preflight inspection of the airplane, verified engine oil level to be about 10 quarts, and noted the oil appeared to be new. During the takeoff climb, he observed the engine oil pressure decreasing. Concerned about the oil pressure indication, he elected to return to the airport. Shortly thereafter, he observed a complete loss of engine oil pressure followed by a total loss of engine power. Unable to make it to the airport, the pilot elected to make an off-airport landing to a nearby road. During the landing sequence, the airplane struck a power line and impacted a utility pole before coming to rest upright.
A review of the airplane’s maintenance records revealed that an annual inspection was completed on April 3, 2024. According to the engine maintenance logbook a serviceable vacuum pump was installed during the annual inspection.
According to the A&P IA, a mechanic trainee performed the maintenance on the accident airplane, and as the A&P IA, he oversaw the work performed by the trainee. He discussed the work scope with the trainee and would periodically check on the maintenance performed. The A&P IA then verified the work conducted; however, he did not verify that the hardware on the engine-driven vacuum pump was tight or set to any specific torque value. After the work was completed, an engine test run was completed and the airplane was returned to the owner.
Postaccident examination of the recovered wreckage revealed that the nose landing gear was fracture separated and the fuselage near the main landing gear exhibited buckling. The left wing was separated at the wing root by recovery personnel to facilitate recovery. The right wing was separated at the wing root and was fractured into numerous sections. The fuselage undercarriage contained oil residue extending along the fuselage to the empennage.
Examination of the engine revealed that it remained attached to the engine mounts. All six cylinders and all engine accessories remained attached. Cracking on the top of engine crankcase was observed between cylinder Nos. 5 and 6. The oil level dipstick did not register any oil within the oil sump.
The engine-driven vacuum pump remained attached to the engine accessory case but was loosely secured to the mounting pad, which allowed for movement between the mounting pad and the vacuum pump. The vacuum pump moved forward and aft on the mounting studs about 1/8 in with minimal resistance. All four of the vacuum pump mounting studs were loose and had backed off from the vacuum pump.
The No. 6 cylinder and piston were removed and a cracked section of the engine crankcase separated with the cylinder. Damage to the interior crankcase near cylinder Nos. 5 and 6 was observed. The cam shaft was fractured at the rotating plane of the No. 6 cylinder connecting rod. The No. 6 connecting rod was separated at the journal end. Dark discoloration, consistent with thermal damage, was observed to the No. 6 connecting rod end and journal. The thermal discoloration and damage were consistent with lubrication deprivation.
The airplane was equipped with a “dry” vacuum pump. However, according to the engine manufacturer, the vacuum pump accessory mounting pad has a drilled passage that supplies pressurized lubricating oil under normal operating conditions for use when utilizing a “wet” vacuum pump. In the case of “dry” pump applications, this oil passage is blocked off by the mechanical clamping force and gasket of the dry pump. If the mechanical clamping force is not maintained, lubricating oil will leak out until the oil sump is depleted of oil.