Understand that the APS5000 used in the B787 is the first all-electric APU for large commercial aircraft.

Source: http://www.pwc.ca/en/engines/auxiliary-power-units

Sorry if this sounds too amateurish, but what exactly is an 'all-electric APU' and how does it differ from past traditional APUs? Does the design allow it to generate the higher electric power required for the B787 and more electrical aircraft?

Any help would be appreciated, thanks!


1 Answer 1


Usually an APU provides electricity and bleed-air, just like the aircraft engines do. An all-electric APU only provides electricity. This can be done in the Boeing 787 because of the bleedless architecture where systems that would normally require hydraulic or pneumatic pressure are fully electrified.

  • $\begingroup$ How does the 787 start its engines without ground power (or following a midair flameout at an airspeed too low for a windmill restart), then? $\endgroup$
    – Vikki
    Commented Jun 12, 2019 at 1:20
  • 1
    $\begingroup$ @Vikki-formerlySean, as long as one engine or the APU is running, the electrical power from that device can drive the starter generator to start an engine. $\endgroup$
    – BowlOfRed
    Commented Apr 22, 2021 at 19:51

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