Boeing 747 auxiliary power unit (APU)
The 747’s APU is a gas-turbine generator in the tail cone running while main engines are off. The 747-400 replaced the classic unit with the far more economical Pratt & Whitney Canada PW901A (two 90 kVA generators); the 747-8’s PW901C ups that to two 120 kVA units.
While the 747 sits at the gate with engines shut down, a small gas turbine in the tail cone — the auxiliary power unit — drives bleed air for cabin conditioning and engine starts, and powers generators for the electrical system. It can also supply emergency backup power in flight.
| Key facts | |
|---|---|
| 747-400 APU | Pratt & Whitney Canada PW901A |
| 747-8 APU | PW901C (derived from the PW901A) |
| Electrical output | 747-400: two 90 kVA generators; 747-8: two 120 kVA generators |
| Role | Bleed air for cabin conditioning and engine start; ground and in-flight electrical backup |
The -400’s PW901A was a new APU for the Series 400 with roughly 40 percent lower fuel burn than the unit it replaced. Its load compressor delivers bleed air for cabin air conditioning and main-engine starting, while the gearbox-mounted generators supply electrical power.
The 747-8’s PW901C keeps the same design but doubles the electrical rating to two 120 kVA generators. Compared with its predecessor, the 1970s-era classic 747 APU burned much more fuel for the same output.
Sources
- Boeing 747-400 guide — Aircraft Commerce
- Commercial auxiliary power units — Pratt & Whitney
- PW901A airworthiness directive — US Federal Register
Sources
Facts on this page are checked against the primary and institutional references below.
- Boeing 747-400 guide — Aircraft Commerce
- Commercial auxiliary power units — Pratt & Whitney
- PW901A airworthiness directive — US Federal Register
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