The DC-9 reportedly already had a problem with either hydraulic pressure or quantity, maybe both. Don't remember if it was the left or the right system. Both systems connect to both braking systems. They tell me that the right engine pump is backed up by an aux. electric pump (3,000 psi, via left gen. bus). The left engine pump is backed up by the alternate pump (1800-2500 psi. via right dc bus), but powered by fluid pressure in right system via "motor/pump" action. Accumulators should give 3-5 brake applications.
The parking brakes supposedly need at least 1400 psi from either system to work. A very rare anti-skid electric (ground shift) failure could cause total braking failure below about 20 knots if switch in armed position on -30 series. Or so they told me.
NWAFlyGirl-I'm not quite sure about any of this system info., but can your flightcrew correct me on some of it? I only learned about this from neighbors on an overnight .
The planes I fly have Pratt & Whitneys with 'autofeather' capability
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