View Full Version : B747-400 QRH: "HYD CONTROL 1,4"
Bluescan
17th Jul 2016, 17:56
Good evening everybody.
In the B747-400 QRH I find the "HYD CONTROL 1,4" NNC.
Why is there no such checklist/advisory message for system 2 and 3?
I've tried to search for an answer to this question but without results, so this might be a no brainier for everyone else.
The only reason I might find is that demand pumps 1 and 4 are commanded ON when selector is in AUTO and trailing flaps are in transit or extended past "1". System 1 and 4 have some quite demanding tasks during takeoff and landing and loss of system pressure is maybe more critical.
Do anybody have some insight in this logic? :)
Best regards,
Bluescan
Intruder
17th Jul 2016, 19:26
Probably the highest demand on the hydraulic system is the landing gear, which are on 1 & 4.
mustafagander
18th Jul 2016, 10:59
It seems pretty straight forward to me. The QRH action is to turn the ADP(s) manually on to potentially avoid slow operation if the control fault is affecting the demand pump sensing. If it is another control fault, no harm done.
Think about the missed approach certification requirements for one.
Just curious... Is the QRH the same on 744s with 4 ADPs?
Willit Run
18th Jul 2016, 16:27
NSEU,
AFAIK, All -400's have 4 ADP's. ( alt.demand pump) However, #2&3 ADP's can be either electric or pneumatic depending on the original operator. All -400's have the #4 system w/ an electric Aux pump and some operators also have the #1 system with an electric aux pump.
spannersatcx
18th Jul 2016, 18:09
I thought ADP stood for Air Driven Pump?
Willit Run
19th Jul 2016, 02:02
Sometimes it does; as on the classic.
The -400 can have either electric or air driven Demand pumps. United elected to go with all four powered by pneumatics. All the ones I have flown, Ex Malaysian, ex JAL, ex ANA, ex cargolux, have electrically powered demand pumps. That seems to be the Boeing norm.
I believe Korean Air Lines also has 4 ADPs (air-driven pumps).
Sorry for the confusion... I've never heard of the expression "Alt Demand Pump". Aux perhaps.
The Air Driven Pumps on the inboards are normally associated with PW engines, so I assumed the extra hydraulic flow was for the reversers. Extra demand was given as a reason for the message inclusion, hence my question.
Cheers
spannersatcx
19th Jul 2016, 11:49
CX, demand pumps are ADP's (Air driven pumps), well the RR ones anyway.
Thanks, Spanners... PW reverser theory abandoned (as reason for ADPs on inboards).
Intruder
19th Jul 2016, 19:51
Our PW-engined 744s still have Air-driven Demand Pumps on 1 & 4, Electric-driven Demand Pumps on 2 & 3, as well as Engine-driven Hydraulic Pumps on all 4.
Bluescan
19th Jul 2016, 22:32
Thank you all. :-)
spannersatcx
20th Jul 2016, 16:26
EDP being Engine Driven Pump!
Funny how abbreviations can lead to such diversity of meaning?
Willit Run
21st Jul 2016, 03:28
And to further confuse things; some operators, (JAL birds) have electric AUX pumps on #1 and #4
And to further confuse things; some operators, (JAL birds) have electric AUX pumps on #1 and #4
Not so uncommon... British, El Al, KLM, Qantas and South African have/have had 2 Aux pumps.
The ultimate gold standard of 744 is
AUX (ACMP) on 1 & 4 (Towing - body gear steering, brakes)
ADP on 1 & 4
ACMP on 2 & 3
The most basic, cheaper, maintain parts commonality with the "classic" is/was
AUX (ACMP) on 4 (brakes)
ADP on 1,2,3 & 4.
Boeing used* to let you customise (added expense to Boeing) however those days are over and the gold standard it is 👍
*Unless you're POTUS, military or just insanely loaded.
The -8.
AUX (ACMP) on 1 & 4 (Towing - body gear steering, brakes)
ADP on 1 & 4
ACMP on 2 & 3