Many modern airliners (Embraer 170/190 and Airbus series in particular, probably more) use a wind-powered turbine as a last resort to pressurize hydraulic systems in the event of total loss of engine power. It automatically deploys when the airplane detects a loss of engine power so the system sees very little if any loss of pressure. Many auxiliary hydraulic devices will be de-powered but key flight controls will continue to operate. Air Transat flight 236's glide to the Azores is a good example of this system in action.