Final answer:
The maximum altitude for using APU bleed air to start an engine depends on the specific aircraft and its engine manufacturer's specifications. Typically, it is up to around 25,000 feet, but it may vary for different aircraft.
Step-by-step explanation:
The maximum altitude for using APU bleed air to start an engine depends on the specific aircraft and its engine manufacturer's specifications. Typically, an APU (Auxiliary Power Unit) provides bleed air to start engines at altitudes up to around 25,000 feet.
However, it's important to note that in some high-performance or military aircraft, the APU bleed air may not be sufficient to start the engines at high altitudes, and an external source of air or an alternate start method may be required.
Therefore, it is crucial to refer to the aircraft's operating manual and follow the manufacturer's recommendations for engine start procedures at different altitudes.