Final answer:
Activating the APU FIRE PUSH switchlight is an emergency procedure to handle a fire in the Auxiliary Power Unit, involving cutting off fuel, discharging a fire extinguishing agent, and isolating the unit electrically and pneumatically.
Step-by-step explanation:
Pushing the APU FIRE PUSH switchlight on an aircraft typically causes several actions to occur. This is a critical action taken when there's an indication of a fire in the Auxiliary Power Unit (APU). Upon activation, the following are generally expected to happen:
- Fuel supply to the APU is shut off to starve the fire of its fuel source.
- The fire extinguishing agent is discharged into the APU compartment in an attempt to put out the fire.
- Electrical and pneumatic connections to the APU may also be cut-off to further isolate the unit and reduce the risk of the fire spreading or causing additional damage.
The exact procedures and consequences can vary depending on the aircraft's make and model, but these are the primary safety functions designed to mitigate APU fire risks.