> ## Documentation Index
> Fetch the complete documentation index at: https://www.narev.ai/docs/llms.txt
> Use this file to discover all available pages before exploring further.

# Engines and APU

Manage thrust, engine starting and APU operation, and monitor engine indications.

Engine 1 corresponds to LEFT engine indications; engine 2 corresponds to RIGHT engine indications. The mapped N2 bindings explicitly identify engines 1 and 2. Use the associated engine throughout each start sequence.

The engine start switches select GRD, OFF, CONT or FLT through named actions. Use the [engine controls](https://www.narev.ai/docs/irl-gym/aircraft/engines/controls.md) to select the start levers independently of the thrust levers. Keep these controls separate. During the normal start, fuel admission occurs at 25% N2; at 56% N2 the procedure calls for verification of start-switch OFF, followed by START VALVE OPEN extinguished and a starter-cutout announcement.

Verify engine 2 stable before engine 1 start. A switch return, an extinguished start-valve indication and stable engine operation are separate conditions. Use the assigned stability criteria; the supplied checklist does not provide a numerical stable-idle band or dwell time.

APU selector position, APU availability, APU electrical supply and APU bleed supply are separate states. APU EGT alone does not establish any of these states.

## Controls and readings

See [the current controls and readings](https://www.narev.ai/docs/irl-gym/aircraft/engines/controls.md) for this system.


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