Originally Posted by Waves

“Reports have the cause as a center hydraulic system failure. If that was the only failure, then the landing gear should have been extended using the Alternate Gear Extension System. The 767 center hydraulic system has two independent AC electrical pumps, an air driven demand pump (ADP), and an emergency Ram Air Turbine (RAT) to power the center system components. The system also incorporates a standpipe in the hydraulic fluid reservoir at 17% to prevent a complete loss of fluid in the event of a component leak. Inoperative items with a complete loss of the center hydraulic system include center auto pilot (A/P), right A/P stab trim, some spoilers, ˝ stab trim, NORMAL flap and gear operation, and auto speedbrake system. Alternate gear extension is fully functional unless this hydraulic failure is accompanied with or caused by a total electrical failure. With a total electrical failure including the depletion of all battery power, a specific hydraulic shuttle valve that is held open electrically will then close and not allow the gear or flaps to be lowered normally or even by using alternate extension methods. A total electrical failure is extremely remote, especially for the 767ER which has an additional hydraulically driven generator (HDG) electrical power source. An electrical failure is not mentioned as a cause, and certainly does not appear to be the case here because the flaps were down. Any single jammed gear or gear door would not prevent the other two from extending. If this less than desirable landing scenario was caused by the failure of the center hydraulic system, then I believe there must have been an electrical failure in the hydraulic shuttle valve as well. In other words, a dual system failure. As unlikely as that may be, it is possible I suppose. Any other 767 drivers have any ideas? Am I missing something? BTW: The 757 hydraulic systems were designed differently to avoid this scenario altogether.”