EHPS: Electric Motor-Driven Hydraulic Power Supply

What it is

A 28 VDC electric motor-driven hydraulic pump installed on hydraulic system 1, ground use only. It provides just enough hydraulic pressure to do the full-and-free flight-controls check on the servo-actuators before either engine — and its mechanically-driven hydraulic power supply — is even running. Controlled from the EDCU HYD page, powered from the helicopter battery, and limited by AMMC logic to 2 minutes of operation maximum. In flight, switching it on is inhibited by design.

Why it changes the start sequence

Without EHPS, engine 1 normally has to start in ACC (accessory) mode first, because the flight-controls check needs mechanically-driven hydraulic pressure that only comes from a running engine. EHPS removes that dependency: run the electric pump on the ground, do the flight-controls check off it, then engine 1 can be started directly in MAIN mode, either engine first. The equivalent flight-controls check step later in the normal Engines Start procedure is skipped, since it's already been done.

Same logic applies in reverse at shutdown — with EHPS installed, engine and rotor shutdown can be done in MAIN mode, since the next flight-controls check will again be available from the electric pump rather than requiring a mechanically-driven source.

The check itself

ELEC PUMP switch on, confirm HYD 1 pressure reads 80–120 bar (this is genuinely in the pump's normal red zone on the gauge — don't read that as a fault). Exercise the controls progressively and slowly: collective to about 50% then cyclic to full displacement, cyclic centered then collective to full displacement, then pedals to full displacement. Deselect ELEC PUMP when done — it also disengages on its own after 2 minutes regardless.

Using EHPS does draw down battery power that would otherwise be available for engine start, so it isn't purely free.