In the event of an engine failure, what function does the AUX hydraulic pump serve on the Challenger 300?

The AUX hydraulic pump in the Challenger 300 is designed primarily to provide hydraulic pressure for the operation of critical systems when the primary hydraulic system experiences a failure. In the case of an engine failure, the AUX hydraulic pump plays a crucial role in ensuring that essential flight control surfaces remain operational. One of these surfaces is the lower rudder's Power Control Unit (PCU), which helps in maintaining control of the aircraft.

This capability is vital because if primary hydraulic pressure is lost (for instance, due to an engine failure that affects the hydraulic systems), having a secondary source of hydraulic pressure like the AUX pump ensures that the lower rudder can still function properly. This enables the pilot to maintain control and assists in stabilizing the aircraft during a potentially critical situation.

While the other options may seem related to aircraft operation, they do not represent the primary function of the AUX hydraulic pump in this context. For instance, it does not provide fuel, assist in cabin pressurization, or act as a backup for landing gear operation. The focus here is on maintaining control surfaces, which is central to flight safety in the event of an engine failure.