What is the function of the EMER FLAP switch when moved to the DEPLOY position?

The function of the EMER FLAP switch when moved to the DEPLOY position is to extend the flaps to 20 degrees and the slats to 25 degrees, regardless of the flap handle position. This feature is essential for ensuring that the aircraft can achieve the necessary lift characteristics in an emergency descent or landing situation, providing pilots with a means to manage the aircraft's configuration even if the primary flap control system is unresponsive or has failed.

This emergency flap deployment is particularly critical during scenarios where the aircraft must be brought down quickly while maintaining control, as the additional lift generated by the extended flaps and slats enables a steeper descent profile while still aiding in maintaining airflow over the wings.

The other options do not accurately describe the function of the EMER FLAP switch. For instance, clearing hydraulic pressure does not pertain to the flap control systems but rather relates to hydraulic system management. Similarly, retracting the landing gear and initiating engine cooling are functions unrelated to flap operation and are governed by separate systems and controls within the aircraft's operational protocols. By understanding these distinctions, one can appreciate the specialized role of the EMER FLAP switch within the broader context of aircraft operation and safety.