beelsebob wrote:But a broken hose isn't the only possible hydraulic failure... What about a broken valve that didn't allow the fluid to drain again? Plus, even a broken hose could cause this failure – e.g. a broken hose on the system that controlled the valve that let fluid out of the DRS. Plus, the DRS might be raised based on a lack of fluid, not based on the presence of fluid, it might need pressure in the system to lower it.
Given that the DRS needs to fail in the down position I would highly doubt that the system uses a reduced pressure to signal to raise the flap as any failure of the pump or hose would cause the flap to open.