View Full Version : Double Hydraulic failure on B777 and more

Pitch Up Authority
1st Jun 2015, 15:43
1) Can anybody tell me if you loose the PFC's in case of a double hydraulic failure on B777?

2) In case of low QTY on hydr sys C the system is split and nose gear isolated. What about the alternate gear extension to nose gear and main gear unlocks, are they also isolated?

Nil defects
1st Jun 2015, 17:52
1 No the PFC's are still available. Flight Controls remain in Primary mode so Auto Pilot is still available. Able to still fly RNAV approaches but not Auto land.

2 Not sure about this question but Alternate Gear extension is always available with Dual Hydraulic failure. (Are the uplocks isolated - need an engineer to explain how the system works mechanically.) I am sure there is some one here who can answer that.

1st Jun 2015, 21:11
http://nsa38.casimages.com/img/2015/05/25/150525063606621642.jpg (http://www.casimages.com/i/150525063606621642.jpg.html)

1st Jun 2015, 21:14
Yes its isolated but only in that the fluid is designed to be trapped in the line to enable the up locks to be released even if the centre system is empty.

Pitch Up Authority
1st Jun 2015, 23:22
Reading the FCOM I would also conclude that the PFC are still there. There is no correlation between the PFC and a double hydraulic failure but this failure would also mean the loss of multiple control surfaces and at higher speeds the outboard ailerons are locked out as well.

I understand your answer but can you confirm that with the EICAS message FLIGHT CONTROLS you are still in Primary Mode?


Nil defects
2nd Jun 2015, 03:28
Yes it is still in Primary mode.

With the EICAS msg FLIGHT CONTROLS you have most likely had a Dual ACE failure. (a highly unlikely event - but stuff happens)