What can result from an APU start accumulator charged to less than 2800 PSI?

A start accumulator that is charged to less than 2800 PSI can lead to a situation known as a hot start. This occurs because the reduced pressure in the accumulator may not supply sufficient hydraulic power to initiate an efficient APU start. In this scenario, the APU may ignite fuel too soon or improperly, leading to an overheated start condition.

Hot starts can damage the APU or affect its operational reliability, which is critical for maintaining the power necessary for aircraft systems during ground operations or when main engines are shut down. The importance of having the accumulator charged to the appropriate pressure is thus emphasized, as it ensures smooth and effective APU starts, mitigating risks associated with hot starts.