View Full Version : ADP Run Logic on 747-400

31st May 2002, 05:23
I seem to recall a previous question on this subject, but can't
seem to find it...

On some 747-400's, the ADP's are activated by "Flaps In Motion"
and "Flaps Out of UP signals" (amongst other things). What
generates these signals?

Flap Position transmitters (L/E? I/B TE? O/B TE Flap?)
Flap I/P actuator feedback?
Flap Lever RVDT's?
A combination of these?

I understand that a specific Flap Control Computer handles each
ADP and that there is no FCU redundancy for ADP control. i.e. The
Right FCU only handles the #1 ADP and the Left FCU handles
only the #4 ADP. Is this correct?


31st May 2002, 14:31
Er... thanks, ASFKAP... Now I have two questions/problems :D

(My original one about flaps... and now a new one about Body Gear Steering).

I have no idea why the BG steering should trigger an ADP to run on a 747-400 (I was under the impression that with the engines stopped, selecting the ADP to AUTO would run the ADP's continuously anyway).


31st May 2002, 15:26
Q & ASFKAP- on the Classic 747, the Nr 1 ADP kicks on at 22.5 deg nose steering angle, just in case it wasn't selected to Auto; its to drive the body gear steering which becomes active at that point.

1st Jun 2002, 10:36
tinyrice, I don't know what kind of 747 Classic you have operated, but all the ones I have in my logbook; i.e -100,-200,-300 with various engines, P&W, RR, CF6, were all the same. ADP operation depended on switch position. In Auto, pump runs when system demand causes EDP output pressure to fall below 2,600 psi. Once started, pump will run for at least ten seconds (or as long as system demand prevails). In off position,pneumatic supply is shut off and pump will not operate. With switch in continuous posn. pump will operate continuously.
I don't know about the -400, they don't have flight engineers on them but I shouldn't think the hydraulic system would differ much from the classic.

1st Jun 2002, 13:31
The ADP's must be in Auto. The FCU R will signal Hyd Sys 1 & FCU L will signal Hyd Sys 4 through there associated HYDIM card. On GE and P & W aircraft the pumps will run continously in flight with flaps extended. On the ground they will only run until flap position matches that of flap handle. As you say there is no FCU redundancy for this feature. If either FCU L or R is inop the flightcrew would have to select ADP 1 or 4 to On manually during landing/take-off. Not sure about the RR equipped aircraft, can you help us out here Spannersatcx?

The B747-200 has none of the above and just uses EDP low presssure (2600psi) as a signal to run the ADP in Auto, it runs for 10 to 12 seconds afgter 2800psi is attained.

As for the Body Gear Steering, we tow with the ADP at Auto so would run all the time.

Hope this is of some help.

1st Jun 2002, 15:58

As I said in my note -"just in case it wasn't selected to Auto".

1st Jun 2002, 16:28
747-400 (GE) #1 and #4 ADP's will run continuously in AUTO if the FUEL CUT-OFF switch is at CUT-OFF. Otherwise they will run in AUTO if the EDP pressure drops below 1400 PSI for longer than 0.3 secs (pump will then run for 14 secs to prevent cycling of ADP). If the TE FLAPS are away from ZERO position in the AIR the ADP will also run continuously . TE FLAP activation is like DENZIL said from the FCU's.
#2 and #3 ACMP's will also run if system pressure drops to 1400 PSI or the FUEL CUT-OFF switch is at OFF.
All logic is processed by the HYDIM.

1st Jun 2002, 21:25
Denzil, got a few days off so not worrying about work at the moment, been fishing and caught some lovely carp today. Will get back to you next week.;)

gas path
1st Jun 2002, 23:20
I see what you mean QAVION the AMM and the schematics are not very good so it's back to the training notes and mine state the right FCU will provide the signal to HYDIM system 1 card to turn on the pump (demand) for hyd. sys.1 whenever the flap control lever is repositioned and until the flaps are in agreement with the flap handle .The left FCU will do the same for sys 4.
So I would guess the answer to you original Q must be the flap handle RVDT:confused: :confused: and the PFM :D in the FCU.

2nd Jun 2002, 01:48
"The left FCU will do the same for sys 4.
So I would guess the answer to you original Q must be the flap handle RVDT and the PFM in the FCU."

Thanks (to all). It's the PFM that I'm interested in.
Is it smart enought to not run the pumps if,
say, Flaps 1 is selected (from up) ...as the leading
edges won't require hydraulics (I guess I should
now redefine my question to only include RR-
powered aircraft, which, as a rule, don't seem to
have the Flaps Out of Up logic). Is the PFM also
magic enough to know when, say, the inboard
TE's only are running out/in (say due to a
drive failure or flap transmitter failure) and will
only run the respective hydraulic system for those
flaps it can control or see the position of.

The logic is probably so complex, I doubt I would
simulate this on the ground (using a real aircraft)..
and I wonder if the accuracy of a simulator would
be able to mimic the failure of specific flap position
transmitters. If there are any RR-powered 744
pilots out there, you may be able to provide the
first piece(s) of the jigsaw puzzle.... Do the ADP's
operate when the L/E flaps are extended to
Flaps 1 in the air? (by observing the Hydraulic
synoptic during this period).

Thanks again!


2nd Jun 2002, 14:53
Before someone corrects me #1 and #4 ADP low pressure should read 2600 PSI and not 1400 PSI.

2nd Jun 2002, 15:35
Hot Dog - you are of course correct, #1 ADP in Auto. I had a brain fart..........

Cornish Jack
4th Jun 2002, 12:02
Hi Q
We did this particular dance some time back. :) It's a funny old logic system and gets its inputs from flap requests and EDP output pressure. The flap logic in 'Roller' powered aircraft is different to the P&Ws and GEs. The flap logic inputs are as given in the MM. The EDP failure case is always looking at the EDP output pressure and, if that drops below the stipulated cut-in pressure, the ADP will run AND CONTINUE TO RUN until the EDP pressure increases above 1600 psi. (N.B. The 12 - 14 second run parameter is disabled as long as the EDP pressure remains below 1600 psi)
When I was still active in the 400 arena, we checked this area with Boeing, including the apparent anomalies of cut-in pressures on RR as against other power plants. I posted the results here about two years or so ago but the recent Pprune software upheaval may well have consigned the archive to the great 'wheely-bin' of the ether.
I will do a search through my papers to see if I still have the original correspondence and post, if successful.

6th Jun 2002, 03:19
"I will do a search through my papers to see if I still have the original correspondence and post, if successful.

Thanks, CJ.

An independent source confirmed a few days ago that the ADP's run on a CF6-powered 744 even when selecting Flap 1 (so I suspect that the logic is fairly dumb, not actually looking at the requirement for hydraulics). This may even be the case when the flaps have switched to Primary Electric ops during a hydraulic flap drive failure.


6th Jun 2002, 21:31
Flaps > 0 in flt and Flaps in transit (magenta on EICAS) on ground, will run ADP's. This is what I originally said!!!! The FCU's will still signal the ADP's to run in Primary Electric mode. as for the logic, it must be simple it's a Boeing:eek:

By the way any jobs going in Oz???? :cool:

7th Jun 2002, 02:17
"Flaps > 0 in flt and Flaps in transit (magenta on EICAS) on ground, will run ADP's. This is what I originally said!!!!"

There was probably still room for abiguity, Denzil (at least in my mind :D ). i.e. Flaps > 0 can mean

1. Flap lever greater than zero
2. TE flap position greater than zero
3. Any flap greater than zero
4. Etc...

Yes, GE/P&W-powered 744's have both "flaps out of up logic" AND "flaps in transit logic" but, unfortunately, the "out of up" logic masks the flaps in transit logic. I'm wondering how the flaps in transit logic behaves by itself (as on the RR-powered aircraft).

"The FCU's will still signal the ADP's to run in Primary Electric mode. as for the logic, it must be simple it's a Boeing "

As a maintenance engineer, that's the way (ah hah) I like it :p

"By the way any jobs going in Oz????"

If there is/was, I'd say chances are that most jobs will be/have already been swallowed up by ex-Ansett personnel (after Ansett's collapse).


10th Jun 2002, 21:59
I think there is some confusion here and since I am currently studying ADP logic on 747s lets see if I can clear this up.

All 747 series aircraft carry the same Fairchild Controls ADP. The design is 35 years old, though there is a replacement that is not only more powerful, but MUCH quieter and is found on the 767 & 777.

The ADP is designed to supplement hydraulic pressure during times of low pressure, failure or when the airplane is configured such that a failure may cause an unrecoverable configuration(ie. can't get the flaps/gear up for go around.

It is different on all three engine configurations as far as where the hydraulic pressure must dip to come on automatically. The RR version comes on first and once on remains that way until cycled(this is due to the RB211 having a small core). The GE and Pratt are relatively the same.

Flap movement on ground can make the ADP come on. Anytime the Flap lever is in excess of 25 degrees the ADP is on and running continually. Excessive control input by the pilot can also make them come on. Fuel cutoff or flow failure causes them to come on sensing the impending engine failure.

Some operators OPs manual calls for the ADP to be set to ON during approach. Most set to Auto.

How you guys like the noise coming off of the ADP?

10th Jun 2002, 22:43
No confusion, the ops are as detailed in the B747-400 training notes and AMM.

11th Jun 2002, 10:24
What I am reading in the Boeing Maintenance Manual (my bible) contradicts a lot of the answers that are being provided here (and by my other, normally reliable source).

The testing of the 747-400 1 and 4 ADP's involves, in one part, the selection of Flaps 5. This seems to suggest that Flaps 1 is insufficient to activate the ADP (It also repeatedly mentions trailing edge flap being greater than 0, not leading edges greater than 0). I don't think the aircraft logic is a dumb as being made out here. Perhaps the confusion is arising from the fact that there are a number of time delays built into the system. If you are retracting flaps after landing to UP, with the engines still running, then the ADP's should run for a minimum of 10 seconds after the TE have stopped moving (talking here about the flaps in motion logic). So the ADP's will still be running with the TE flaps up and probably after the LE flaps have retracted also.

If someone could confirm, on departure (after pushback/on the ground), with the engines running on a RR, GE or P&W -powered 747-400 that the selection of Flaps 1 only (no further) from UP, will not activate the ADP's, I would be most appreciative.
If the Boeing Maintenance Manual is wrong, as it sometimes is (just as pilots' manuals are), then I will gladly let Boeing know.


11th Jun 2002, 13:33
From Doc 29-11-08......"When engine driven hydraulic pressure falls below 2600 +/-50 psig or the aircraft flaps are set to greater than approximately 25 degrees, the turbine(ADP) assemblies will automatically start up to provide additional hydraulic pressure."

Now we do have a noise issue during taxi at some major EU airports caused by the ADP. Depending on what the piltos are doing the Hydraulics can get taxed during taxi to Takeoff and the ADPs come on. At idle all the way up to approach power the ADPs are louder than the engines themselves. This happens more often on RR powered airplanes than the GE or the Pratt. Also the RR configuration is different than the GE or the Pratt such that it allows more noise to escape out the boat tail.

From what the hydraulics guys are telling me, flushing a toilet can cause the ADPs to come on.

Oh, there are two configurations on ADP and are operator specified.... The operator can specify 2 per wing or 2 per airplane. Have no info on which configuration is more prominent out there.

16th Jun 2002, 06:05
"No confusion, the ops are as detailed in the B747-400 training notes and AMM."

And what if the two books disagree, Denzil? ;)

In the face of such confusion, my "source" has agreed to humour me and recheck his findings (hope to get an answer next week).

According to my airline maintenance manuals for the GE powered 747-400, the following applies:

AUTO Operation For #1 ADP

1) #1 Engine Fuel valve Closed (in the air or on the ground) = ADP #1 runs

2) "TE Flaps" In Transit (air or on ground) = ADP #1 runs

3) "TE Flaps" not zero (in air) (for 0.3 seconds) = ADP #1 runs (for a minimum of 10 seconds)

4) #1 EDP less than 1400psi (for 0.3 seconds) (air or ground) = ADP #1 runs (for a minimum of 14 seconds after EDP returns to 1600psi).

For the RR-powered 747-400 #1 ADP

1) #1 Engine Fuel valve Closed (in the air or on the ground) = ADP #1 runs

2) "TE Flaps" In Transit (air or on ground) = ADP #1 runs

3) #1 EDP less than 2600psi (for 0.3 seconds) (air or ground) = ADP #1 runs (for a minimum of 14 seconds after EDP output returns to 2,825psi).

I haven't any values for P&W aircraft, but they probably have the additional logic for Flaps Out of Up, like the GE-powered aircraft.

747 Focal...

I'm glad to say I haven't yet come across a case of flushing toilets activating these pumps :D ... but, yes, air-driven demand pumps can be very noisy at times....especially if there are four of them fitted (as often seen on P&W-powered aircraft). However, when recently checking for #4 ADP ops after pump control problem rectification, I couldn't hear it start up or shut down above the noise of the packs (I was standing at the nose gear with phones on at the time). Perhaps because the air vent for the #4 ADP is on the right hand side of the strut. I had to walk towards the engine to be able to hear it.


17th Jun 2002, 13:56

Thanks for the info. From what I can tell, and I would think where I am at, that there is a lot of literature on the ADP operation and none of it seems to agree.

The placement of the cooling intake and the exhaust was most probably responsible for you not being able to hear the ADP until you moved. They are designed to reflect away from the cabin.

Testing them this month and next at Paine. Hopefully the functional test guys will know how they are supposed to operate.


22nd Jun 2002, 03:06
Here's an update on the ADP logic to add to the confusion....

My source tells me that he tried selecting Flaps 1 from Up on departure (in a 747-400 with GE engines)... and the ADP's did not run. This seems to fit the Boeing Maintenance Manual's "TE only" logic (on the ground with engines running). However, he tells me that when he went from landing config to UP in one go at the end of the flight, the ADP's didn't stop running until the flap indicator showed UP (i.e. LE's and TE's).

Perhaps there is some kind of EICAS indication delay, rather than a glitch in the logic? (e.g. after the TE flaps had stowed an electrical signal would have to be sent to the ADP via cards, wiring, etc and the ADP valve would have to close. The closed signal would then have to go to EICAS via wiring/computers, etc, to display the ADP-not-running indications. Perhaps by the time all this had happened, the inboard LE's would have already retracted?).