Auxiliary Power Unit
Also from: APU
The B737NG uses the Allied Signal 131-9(B) APU, which is FADEC controlled and can be started up to 41,000'.
Limitations
Bleed + Electric | 10,000' |
Bleed | 17,000' |
Electric | 41,000' |
Operate the APU for 1 minute prior to using bleed air. Can supply bleed air for 2 packs on the ground or 1 pack inflight(1).
References
(1): FCOM Vol 2 2.30.1