What altitude should pilots avoid exceeding when using APU bleed?

When using the Auxiliary Power Unit (APU) for bleed air, it is critical for pilots to avoid exceeding a specific altitude to ensure safe operation and optimal aircraft performance. The correct altitude limit is 15,000 feet.

Above this altitude, the performance of the APU's bleed air may be compromised due to the lower atmospheric pressure and temperature. At higher altitudes, the APU’s ability to supply sufficient bleed air for environmental systems can diminish, which may affect cabin pressurization and air conditioning. This limitation is set to ensure that systems relying on bleed air function effectively and that pilot and passenger comfort is maintained.

Adhering to this altitude restriction helps prevent scenarios where inadequate air supply could lead to malfunctions or uncomfortable cabin conditions. Therefore, it's important for pilots to be aware of these operational parameters to make informed decisions during flight.