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Whatever CRJ 700 or Learjet 35A/45XR.

Do these aircraft have full manual reversion? Can you operate the flying surfaces in a hydraulic failure?

These aircraft are very small – even smaller than a 737 – so I guess they all do.

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    $\begingroup$ CRJ's have Ram air turbine which will power hydraulic system 3 in case everything fails. 737 don't RAT so they have to have manual controls. $\endgroup$ – Andrius Oct 21 at 14:48
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Can't speak for the Lear, which I believe has manual controls anyway, but the CRJs DO NOT have manual reversion. The RJs are designed to a technical level similar to the Boeing 767.

The control surfaces are purely hydraulically operated. For elevator and rudder, which have 3 PCUs each, you'd have to lose all 3 hydraulic systems to lose the surfaces. For the ailerons, which are 2 PCU and split one of them on each side to Hydraulic System 2 and 3 while the others run on System 1, you have to lose 2 systems to lose one aileron, and all 3 to lose both ailerons.

The probability of this kind of multiple failure event is below the 1:1,000,000,000 risk threshold for catastrophic events, so it's good to go.

It's been discussed before how the hydraulic PCU can kind of be driven manually by hauling on the controls to lever the PCU piston about the bottomed-out servo control valve, but this would only give a bit of movement at the limits of control travel in any case and is not a practical consideration for trying to control the aircraft in flight.

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    $\begingroup$ Q400: the ailerons are manual. Hyd1 and 2 power the rudder and spoilers. Hyd1, 2 and 3 power elevators. Global Express: triple hydraulic redundancies in all three axes. $\endgroup$ – JZYL Jul 6 at 6:17
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    $\begingroup$ The pre-400 D-8s are only hydraulic for rudder. Elevators use spring tabs for servo boost. The 400 was overdesigned and this hurt it with operators who were better suited to the simple mechanicals of the older ones and it lost ground to the simpler to maintain ATR 72. They should have just stretched the 300 with minimum changes. $\endgroup$ – John K Jul 6 at 15:31

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