Engine Compartment Purging System

The engine compartment can be purged by releasing an inert gas (helium) under pressure into the area to extinguish a fire or relieve an over heat condition.

Three cubic feet of helium is stored in two spherical containers under 3600 psi pressure. The containers are on either side of the engine compartment in the left and right wing root fairing tunnels. Either automatic or manual release of helium can be selected by the pilot. Because of the location of the two containers adjacent to the engine compartment, any high temperature condition in the compartment will affect these containers and create a potential explosion hazard. As the helium is released into the engine compartment, it inhibits any fire condition and at the same time eliminates the explosion hazard.

Note: Helium for purging of the engine compartment (or extinguishing an engine fire) is obtained from the 0.491-cubic-foot bottle (located in the 29-inch fuselage extension) on the X-15A-2 SE addon. Helium pressure in the 0.491-cubic-foot bottle can be monitored on the auxiliary pneumatic and control pressure gauge [21, fig. 5-3] on the center pedestal. For more details, refer to "External Tanks and X-15A-2 Systems".

Helium release selector switch.

Helium Release Selector Switch

This 3-position switch [1, figure 5-1], labeled "HE REL SW", is on the left side of the instrument panel. It permits the pilot to select the type of engine compartment purging (either automatic or manual) in case of a fire indication. The switch is powered by the battery bus.

The AUTO position sets up an entirely automatic sequence if a fire occurs in the engine compartment, as indicated by illumination of the fire-warning light [47, figure 5-1]. The engine is shut down, and the helium from the two containers outboard of the engine is jettisoned into the engine compartment to inhibit the fire or overheat condition and to prevent over-pressurization of the containers by extreme temperature increase.

The OFF position sets up the fire detection system for illuminating the fire-warning light only, in case a fire occurs. It will then be necessary either to move the switch to ON to release the helium into the engine compartment without affecting engine operation, or to move the switch to AUTO to release the helium and simultaneously shut down the engine.

Moving the switch to ON will release the helium into the engine compartment whenever the battery bus is energized. Once energized, the helium release valve is locked in the jettison position and must be electrically unlocked by ground personnel.

Known Issue

Due to software limitations in the simulator, fire extinguishing can be performed only once during a flight. The flight should be reset or a new flight initiated for the simulator's extinguisher to recharge.