LMF5000
11th Apr 2015, 14:10
I've been familiarising myself with the Boeing 777's systems (just for fun) using a recreational simulation package. My day job deals with engineering in smaller jets (mainly Bombardiers) so I'm familiar with general aircraft internal workings, but there's one behavour of this 777 simulator that has me stumped.
My question is, why do you lose the engine driven hydraulic pumps if you lose AC power?
The left and right hydraulic systems of the 777 each use an engine-driven main pump (EDP) and an electrically-driven demand pump. With the engines running, if all electrical AC sources are switched off (i.e. L and R engine-driven generators, backup generators and APU gen), the electrically driven pumps switch off as expected. However the L and R EDPs also switch off, as a result of which the left and right hydraulic systems depressurise.
Is this a quirk of the simulator, or a feature of the real aircraft? I've been unable to find any reference to this in the FCOMs, and looking at the datasheet for the actual EDPs used on the 777 [document here (http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&allowInterrupt=1&RevisionSelectionMethod=LatestReleased&Rendition=Primary&dDocName=PCT_289998)], the pump appears to be all-hydraulic (no electrical requirements), so there seems to be no reason why it should't work if the engines are running and only the electrical supplies have failed.
My question is, why do you lose the engine driven hydraulic pumps if you lose AC power?
The left and right hydraulic systems of the 777 each use an engine-driven main pump (EDP) and an electrically-driven demand pump. With the engines running, if all electrical AC sources are switched off (i.e. L and R engine-driven generators, backup generators and APU gen), the electrically driven pumps switch off as expected. However the L and R EDPs also switch off, as a result of which the left and right hydraulic systems depressurise.
Is this a quirk of the simulator, or a feature of the real aircraft? I've been unable to find any reference to this in the FCOMs, and looking at the datasheet for the actual EDPs used on the 777 [document here (http://www.eaton.com/ecm/idcplg?IdcService=GET_FILE&allowInterrupt=1&RevisionSelectionMethod=LatestReleased&Rendition=Primary&dDocName=PCT_289998)], the pump appears to be all-hydraulic (no electrical requirements), so there seems to be no reason why it should't work if the engines are running and only the electrical supplies have failed.