PPRuNe Forums - View Single Post - [B777] Why can't APU support hydraulics but RAT can?
Old 10th Apr 2017, 23:36
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Jet II
 
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Just a point of interest - the APU doesn't supply pneumatics above 22,000 ft so Hyd ADP will be unavailable and even below that altitude the mass flow from the APU isnt really enough to drive the ADP's at the correct speed.

As other posters have mentioned the APU does provide the electrical power to drive the elec Hyd pumps so indirectly it does provide hyd redundancy.
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