Boeing 777 HYD QTY LOW C .
I recently encountered a HYDR C leak, after 3 hours of flight we were confronted with the EICAS msg HYD QTY LOW C and the msg RESERVE BRAKES/STRG. The system indicated a qty of 0.39. within 30 minutes it was down to 0.30.
So we diagnosed this as a real leak and not an indication problem.
We calculated that the system would be empty within 1,5 hours. The remaining flight time was more than 3 hours. So we would be soon without the hydr c system.
We decided to switch off all hydr pumps from the center hydr system, hopefully to stop the leakage. After switching off all the pumps the leak stopped indeed.
We did this to preserve the oil for the Center system for the approach and landing, so we could use normal gear and flap extension, Have full available spoilers, flight controls, brakes, and nose wheel steering.
This worked, we landed with an hydr qty of 0.06 and the NWS even worked, so we could taxi to the gate.
After talking to our tech pilot and ask him why this isn't a standard procedure, he told me that Boeing said the following about this:
Boeing procedures do not endorse preemptive shutdown of hydraulic systems due to low quantity indications. In the event a hydraulic system continues to lose fluid, the appropriate hydraulic pressure message will annunciate the condition. Boeing procedures for low hydraulic quantity do not shutdown the associated hydraulic system for the following reasons:
Since the leak rate is not known, the flight crew may be shutting down a system which may have continued to work for the remainder of the flight. The flight crew will also need to remember to turn the system back on.
Roll rate and speed brake effectiveness may be reduced when a hydraulic system is shut down.
False quantity indications have lead to unnecessary shutdowns and diversions which increase risks to crew and passengers.
There have been cases where cold temperature shrinkage of hydraulic quantity has led crews to shut down an operative system.
Thoughts?