The aircraft’s vacuum system provided a means of powering some of the flight instruments. This system consisted of a vacuum pump on each engine, two relief valves, vacuum manifold, operating instruments and necessary plumbing. The manifold had check valves to prevent reverse flow and vacuum loss in the event of failure of either vacuum pump. Hoses were routed from the manifold to the directional gyro, artificial horizon (AH) gyros and the suction gauge.
The left engine vacuum pump was examined and exhibited body damage, but the frangible drive mechanism was intact. Disassembly of the vacuum pump revealed a fractured rotor; however, the carbon vanes were intact and operated normally. Evidence of rotational scoring was observed on the external surfaces of the rotor components (Figure 8).
