Boeing 747 pneumatic and bleed-air system
High-pressure bleed air from the engines and APU is the 747’s working utility supply: it powers air conditioning, cabin pressurisation, engine and APU starting, and wing anti-ice. Only the 787 abandoned bleed air; the 747 kept the conventional architecture.
The 747 “bleeds” high-pressure, high-temperature air from its engine compressors and uses it as a workhorse utility supply: air-conditioning packs, cabin pressurisation, engine and APU starting, and wing and engine anti-ice all depend on it. It is why the 747 belongs to the “conventional” pneumatic generation of airliners.
| Key facts | |
|---|---|
| Source | Engine compressors, plus the APU when engines are off |
| Users | Air conditioning packs, pressurisation, engine/APU starting, wing and engine anti-ice, some pneumatic actuation |
| Ground need | A ground pneumatic (bleed-air) supply heats or cools the cabin while engines are shut down |
| Exception | The Boeing 787 is bleedless; the 747 was not |
Modern turbofans such as the JT9D, CF6, RB211 and PW4000 supplied plenty of hot, high-pressure bleed air, but it carries a small fuel-efficiency penalty — the air is “stolen” from the compressor path.
The 747-400 and 747-8 use the same philosophy: bleed air from the engine fan/core stages is conditioned and distributed to the packs. Boeing documents ground pneumatic power requirements for heating and cooling in the 747-8 airport-planning manual.
Sources
- Bleed air article — Wikipedia
- Aircraft Icing Handbook — FAA
- 747-8 Airplane Characteristics for Airport Planning — Boeing
- Boeing 747-400 Master Minimum Equipment List — Transport Canada
Sources
Facts on this page are checked against the primary and institutional references below.
- Bleed air article — Wikipedia
- Aircraft Icing Handbook — FAA
- 747-8 Airplane Characteristics for Airport Planning — Boeing
- Boeing 747-400 Master Minimum Equipment List — Transport Canada
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