What is an indication of a bad hydraulic pump in an aircraft?

A bad hydraulic pump in an aircraft typically manifests through a loss of hydraulic pressure or erratic operation of control surfaces. The hydraulic system is vital for controlling various components of the aircraft, and when the pump fails, it can lead to insufficient fluid movement or inconsistent pressure output. This results in the inability to effectively operate the flaps, ailerons, elevators, or rudder, causing them to operate unpredictably or not at all.

A loss of hydraulic pressure indicates that the pump may not be supplying the necessary fluid for effective operation, and erratic behavior suggests that, even if pressure is present, it is not stable enough to maintain controlled movements of the aircraft surfaces. These symptoms are critical for aircrew to recognize, as they can impact the aircraft's handling and safety.

While an increase in hydraulic pressure might suggest a mechanical issue, it generally does not indicate a bad pump. Similarly, a consistent noise during operation may be normal or arise from other factors within the system, and no change in hydraulic pressure might not definitively point to pump failure. Thus, identifying loss of pressure or erratic control surface movement is the most reliable indication of a malfunctioning hydraulic pump.