N6748VBeech 58TC · 1980

On October 11, 2021, about 0857 mountain daylight time, a Beech 58TC airplane, N6748V, was destroyed when it was involved in an accident near Mesa, Colorado. The pilot was fatally injured. The airplane was operated as a Title 14 Code of Federal Regulations Part 91 personal flight.

Fixed-base operator employees at Blake Field Airport (AJZ), Delta, Colorado, stated that, before the airplane departed, the pilot fueled the airplane with 100 gallons of 100 low-lead aviation gasoline. The airplane taxied away from the fuel pump about 0839 and proceeded to runway 3. The airplane departed about 0843 and proceeded northeast toward its destination, Southwest Wyoming Regional Airport (RKS), Rock Springs, Wyoming. The employees also stated that this flight was the first one after the airplane’s latest annual inspection, which had been completed on October 1, 2021.

Automatic dependent surveillance-broadcast data revealed that the airplane proceeded northeast for about 4 nautical miles and then turned left to a north-northwest direction and climbed over Grand Mesa. Recorded air traffic control communications revealed that, about 0852, the pilot reported climbing through 11,000 ft mean sea level (msl) for 14,000 ft msl. After crossing over Grand Mesa, the airplane reached an altitude of about 14,000 ft msl. At 0855:51, the airplane turned right, descended about 1,000 ft, and then climbed to 15,000 ft msl. At 0856:26, the airplane descended rapidly toward terrain. At 0857:00, the controller asked the pilot, “did you get an updraft, mountain wave out there? I’m showing you 800 ft high.” The pilot did not respond to this transmission. Figure 1 shows the flight track and the accident location.

Figure 1. Flight track and accident location.

The pilot’s four most recent training flights conducted with a flight instructor were completed in a single-engine Cessna 172 airplane. The pilot’s recent training experience with emergency procedures in the accident airplane make and model could not be determined.

At the time of the airplane’s most recent annual inspection, the airplane had accumulated 3,429 hours of total time. Maintenance documentation from the most recent annual inspection listed a discrepancy of oil around the right engine propeller governor. The corrective action, according to the maintenance documentation, was to remove the “left” engine propeller governor and install a new gasket. The mechanic who completed the maintenance work stated that the reference to the left engine in the paperwork was a mistake and that he installed a new gasket on the right engine propeller governor.

A review of meteorological information revealed the potential for lighttomoderate turbulence and mountain wave activity near the accident site. The National Weather Service had no active AIRMET, SIGMET, convective SIGMET, or center weather advisory for the route of flight.

At the time of the airplane’s most recent annual inspection, the airplane had accumulated 3,429 hours of total time. Maintenance documentation from the most recent annual inspection listed a discrepancy of oil around the right engine propeller governor. The corrective action, according to the maintenance documentation, was to remove the “left” engine propeller governor and install a new gasket. The mechanic who completed the maintenance work stated that the reference to the left engine in the paperwork was a mistake and that he installed a new gasket on the right engine propeller governor.

The airplane impacted a rocky mountainside about 25 nautical miles north of AJZ and remained upright on a heading of about 040°. The wreckage debris path was about 30 ft long and consisted mostly of paint chips, shards of windscreen, various small debris, and a large outboard section of the right wing that had separated on impact. The empennage was distorted to the left and remained partially attached to the rear fuselage.

The bottom of the airplane exhibited impact damage and scoring from the rocky terrain. The left engine was mostly separated from the left-wing nacelle, and the right engine remained attached to the right-wing nacelle. The six propeller blades were relatively undamaged and did not exhibit leading-edge damage or scoring.

The pilot’s lap belt was found unlatched at the accident site, and no evidence showed stretching in the belt webbing. The pilot’s three-point shoulder harness was found unlatched and behind the pilot’s seat.

The throttle levers were found near the idle position. The mixture and propeller levers were in intermediate positions that were near full forward. Both ignition switches were found in the OFF position.

The right engine was still mostly attached to the nacelle via the engine mounts. The engine compartment, propeller blades, and right-side nose compartment were covered in a layer of engine oil. The oil sump was crushed upward and punctured by the oil dipstick tube. The oil sump was removed; no signs of debris or catastrophic engine failure were evident. The propeller remained attached to the crankshaft.

The turbocharger, fuel control, turbocharger controller, and associated plumbing were separated from their respective mounts but remained connected to each other. Multiple oil and fuel lines were fractured and separated at the fittings. The turbocharger wastegate valve was fractured from the valve control housing at the base. The wastegate control was removed from the turbocharger housing mount and examined.

The turbocharger compressor housing was fractured and separated from the turbocharger due to impact. The turbine rotor was in contact with the housing and was seized. No evidence indicated any rotational damage on the rotor assembly. The oil line from the turbocharger wastegate control valve outlet to the inlet side of the turbo pressure controller was loose at the wastegate outlet end. During the examination, the B-nut was rotated about three-quarters to one full rotation clockwise before the fitting tightened against the mating surface of the flared union fitting.

The fuel rail tube assembly was in place and attached, but the connections were not tight. The fuel injectors were removed from the cylinder heads and were found to be free of obstructions. During removal of the fuel injectors, only two to three threads were engaged.

The propeller governor had fractured near the mounting base. The top mounting studs were bent slightly upward. The lower forward mounting nut was not secure and turned counterclockwise with light finger pressure. The top forward and lower rear mounting nuts were not tight and turned easily with a wrench. The top rear mounting nut was tight. The black gasket was torn and damaged at the top near the edge of the unit exterior. The lower area of the gasket did not have any damage or indentions.

The two mechanics who performed most of the maintenance during the airplane’s most recent annual inspection both stated that they were not sure how the right engine fittings would have become loose after the annual inspection. The mechanic who worked on the right propeller governor stated that he was not sure why the propeller governor was not torqued after it was reinstalled. He was also not sure how the turbocharger oil lines and other fittings became loose because he did not remember performing maintenance on those fittings.

The other mechanic, who held an inspection authorization, stated that he was not sure how the loose fittings would not have been caught during the annual inspection signoff. Typically, mechanics review the airplane twice to ensure that all items were reinstalled correctly. This mechanic did not know why the turbocharger lines or fuel rail would have been taken apart or loosened for the annual inspection because no discrepancies were related to these items.