APU bleed air altitude for one-pack operation is up to what altitude?

APU bleed air altitude for one-pack operation is up to what altitude?

• A. 20,000 ft
• B. 25,000 ft
• C. 15,000 ft
• D. 18,000 ft

Answer: (A)

The air conditioning packs need a steady supply of bleed air to condition the cabin. When the APU provides bleed air to run just one pack, the amount of air and pressure from the APU is sufficient only up to about 20,000 feet. Above that altitude, the available bleed air flow from the APU isn’t enough to meet the pack’s cooling/heating demand with only one pack, so you’d need to use two packs (or engine bleed air) to maintain the required cabin conditions. In short, the APU can feed a single pack up to 20,000 feet because the bleed air flow from the APU becomes insufficient beyond that point.

The air conditioning packs need a steady supply of bleed air to condition the cabin. When the APU provides bleed air to run just one pack, the amount of air and pressure from the APU is sufficient only up to about 20,000 feet. Above that altitude, the available bleed air flow from the APU isn’t enough to meet the pack’s cooling/heating demand with only one pack, so you’d need to use two packs (or engine bleed air) to maintain the required cabin conditions. In short, the APU can feed a single pack up to 20,000 feet because the bleed air flow from the APU becomes insufficient beyond that point.