When the fire switch is pulled, the switch isolates the  following aircraft systems from the engine: If an engine has a fire, the engine fire detection system gives a  fire warning in the flight deck. The engine fire warning lights  come on to identify which fire switch to use to extinguish the  fire. The solenoid in the fire switch energizes and releases the  switch so that the fire switch can be pulled. If the solenoid  does not energize, push the fire override switch to release  the fire switch manually. When the fire switch is pulled, it stops the engine, and the fire switch isolates the engine from  the airplane systems. If an engine has a fire, the fire warning light comes on and the  solenoid energizes to release the switch. When the solenoid  is energized, the fire switch can be pulled. When the fire detection system malfunctions or the solenoid  is defective, and the flight crew wants to extinguish an engine  fire, someone must push the fire override switch. The fire  override switch allows the fire switch to be pulled when the  solenoid is not energized. When the fire switch is pulled, the  push-pull switch contacts operate electrical circuits that stop  the engine and isolate it from the airplane systems. With the  switch pulled, it can be rotated to left or right to a mechanical  stop at the discharge position. The rotary switch contacts  close and operate the fire extinguishing system. If the fire warnings do not go away when the switch is pulled,  position the switch to the DISCH 1 or DISCH 2 position, and  hold the switch against the stop for one second. This fires  the squib in the fire extinguisher container and releases the  fire extinguishing agent into the engine nacelle. Ensure that  the engine bottle discharge light comes on. If the first bottle  does not extinguish the fire, the switch must be placed to the  other DISCH position. This fires the squib for the other bottle. Figure 9-24.  Location of fire extinguishing bottles. 9-17 Left engine Right engine Bottle 1 Bottle 2 L E F T 1 2 DISCH R I G H T 1 2 DISCH ENG BTL 1 DISCH ENG BTL 2 DISCH ENGINE FIRE PANEL (P8) Discharge assembly To discharge nozzles Check valve Discharge manifold To discharge nozzles Pressure switch Engine Fire Operation •  Closes the fuel spar valve •  Deenergizes the engine fuel metering unit (FMU)  cutoff solenoid •  Closes the engine hydraulic pump shutoff valve •  Depressurizes the engine driven hydraulic pump valve •  Closes the pressure regulator and shutoff valve •  Removes power from thrust reverser isolation valve •  Trips the generator field •  Trips the backup generator field  [Figure 9-27] Figure 9-23.  Fire extinguishing bottle. Identification plate Pressure switch test button Safety relief and fill port Handle Mounting lug (4) Discharge port (2) Discharge assembly (2) Pressure switch Squib (2) Pressure switch  electrical  connector