Loose nut leads to engine failure

Aircraft: Cessna 310. Injuries: 1 Fatal. Location: Tupelo, Mississippi. Aircraft damage: Destroyed.

What reportedly happened: The airplane had just undergone an annual inspection, at which time the left engine’s number two cylinder was replaced.

To facilitate the cylinder replacement, the B-nut attaching the fuel supply hose to the engine’s manifold valve was removed, then later reinstalled. A post-maintenance engine ground run was performed, and no discrepancies were noted.

The airplane was cleared to depart from runway 36. According to witnesses it lifted off, and at an estimated altitude of 300 to 500 feet about mid-field, the left engine lost power. The plane turned to the west and began to descend. It crashed on a nearby road, hitting a vehicle and a tree before coming to a stop in the front yard of a house.

The post-accident examination revealed that both propellers were in a low pitch position. The right propeller hit while operating at high power, and the left was operating with low power or was windmilling at time of impact.

The on-site wreckage examination found that the B-nut connecting the fuel supply hose to the manifold valve on top of the left engine had backed off about a quarter turn. The B-nut was tightened, and both engines were test run after the accident and no abnormalities that would have prevented normal operation were found. Both engines produced production-rated power.

After completion of the left engine test run, the B-nut between the fuel supply hose and the manifold valve was set at finger-tight torque. A wire was attached to loosen the B-nut during the engine run, and a stop was in place to limit the rotation. The engine was started and set at full throttle and the B-nut was loosened to slightly over a quarter turn. When the B-nut was loosened, the engine immediately lost power.

Investigators determined that it is likely that the B-nut had been tightened sufficiently to maintain torque during the ground run, however, the vibration of extended engine operation during takeoff led the B-nut to back off, resulting in the loss of power in the left engine.

Investigators noted that there was an open field located past the departure end of runway 36. However, the pilot turned left after the loss of engine power, which was contrary to the departure instructions and contrary to the safest option for an emergency landing, which would have been the remaining runway or the open field. Further, the propeller blades were in the low pitch position, indicating that the pilot didn’t perform the engine failure checklist, which stated that the propeller should be feathered. It is likely that the pilot was delayed in his reaction to the sudden loss of thrust from the left engine and could not maintain airspeed or straight ahead flight.

Probable cause: The pilot’s delayed reaction in performing the engine failure procedures and his failure to maintain adequate airspeed, which resulted in a loss of airplane control. Contributing to the accident was maintenance personnel’s improper torquing of the B-nut between the fuel supply hose and the manifold valve.

NTSB Identification: ERA11FA458

This August 2011 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

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