General Authority of Civil Aviation (GACA) Aeronautical Information Publication (AIP) Practice Exam

At what altitude is the APU bleed air available in flight?

1. 10,000 feet

2. 15,000 feet

3. 22,000 feet

4. 30,000 feet

The correct answer is: 22,000 feet

The correct answer indicates that APU bleed air becomes available in flight at 22,000 feet. This altitude is significant because it typically marks the point at which aircraft systems may engage backup power and start to utilize auxiliary power units (APUs) to supply bleed air for cabin pressurization and other pneumatic needs. The choice of 22,000 feet is set to ensure that adequate engine performance and environmental conditions are maintained. Below this altitude, the onboard engines are typically capable of meeting the demands for air conditioning and pressurization without the assistance of APU bleed air. As altitude increases, the air density decreases and the demand on the aircraft systems changes, making APU bleed air a valuable resource. The other altitude options do not accurately reflect the operational parameters set for APU bleed air. For instance, 10,000 feet and 15,000 feet are generally too low for APU engagement in terms of bleed air requirements, as aircraft systems function sufficiently without it up to those altitudes. Meanwhile, 30,000 feet marks a higher operational environment where the APU is often already engaged for various systems, but the key phrase in the question is about when bleed air specifically becomes available, which is ideally noted at 22,