hydraulics loss

[alexban]

As I understood from a previous thread the DHL incident in iraq left the plane with no hydraulics due to a missle hit near the tip of the wing(the eileron,I think).
I'm wondering,would it be possible to have such a failure to lose all the hydaulic liquid? For ex on the 737 all systems power the flight controls.
Can it be possible to have a leaq ,for ex at the eileron,through which to lose the liquid from all hyd systems? Just at the eileron activating system,after the selecting valve.
I know about the DC10 ,but it was somehow different case.
Brgds Alex

[BOAC]

Alex - I do not have this information for the 737, but with the DHL a/c I understand from the pprune posts that there was one point in the wing at which all the hydraulic lines met, so perhaps it is possible too on the 737. We need an 737 engineer to tell us..................

It would not be 'your day' if it happens and you have to hope you are as skillful as the DHL crew!

[Lu Zuckerman]

To: alexban


Good design practice dictates that the hydraulic system have built in redundancy. Most large civil aircraft have three hydraulic systems and some have electrically driven pumps for backup and still more have the ability to power up one system from another using a series of isolation valves that can be commanded to open and drive a hydraulic motor which in turn drives a hydraulic pump. This usually works in the event of an engine driven pump failure but will not function if the system has lost all of its’ fluid.

In the situation you described the aileron servo would have to suffer multiple structural failures in order to lose the two different systems that supply pressure. In the event of fluid loss the reservoir will isolate itself when the fluid level gets to a specified point.

It is difficult to conceive of a total loss of hydraulics under normal conditions. However if there is some external force such as that on the United MD-11 in Chicago that had an engine tear loose and fracture the hydraulic lines from all three systems. (Or, was it a DC-10)? The United DC-10 in Sioux City had an uncontained engine failure, which cut all three hydraulic lines. (Or, was it a MD-11)?

Forgive me, I’m 73 years old, and my memory is fading fast.

[DDG]

alexban,
If you have a hydraulic leak on a B737 classic or NG the System B hyd reserviors will loose fluid down to the level of the standby standpipe located with-in the reservior(assuming the crew have allowed fluid to continue to leak past the standpipes located with-in each reservior for each system electric driven hyd pump).
The Stand pipe with-in system B hyd will save the fluid below the standpipe for operation of the Standby Hyd system.This system will provide hyd power to the standby rudder (also WTRIS system in the NG)and the thrust reversers,and leading edge flaps/slats.
The trailing edge flaps will run electrically.
All other flight control will be using manual reversion.
Also note that the ailreon system has an actuating Power Control unit for each hyd system,they use independant inputs and each are capable of operating the entire aileron system by themselves so the odds of the failure you mention are extreme to say the least.

Note also that wide body (& A320 narrow body jets) use totally hyd powered flight controls that utilize 3 to 4 seperate systems with multiple redundances.

Regards DDG