747-400 PILOTS ADP ?

[747FOCAL]

What position do most companies want the ADP switch set to on approach? On Off or Auto?

Be helpful if I knew the engine type as well and airline.

Thanks much. :)

[JJflyer]

Primary function of ADP is to provide hydraulic pressure in high-demand situations such as gear and flap cycles. ADP runs automatically to supplement EDP. This provided, that individual hydraulic system switch, is in auto position.

[747FOCAL]

I am looking for operationally what 747-400 pilots are doing at LHR to be specific. On Off or Auto. Thanks for the input.

[Wide-Body]

In auto unless in non normal situation
regards
Wide

[Captain Airclues]

They are called 'Demand Pumps' on the 747-400. Systems 1 and 4 have air driven demand pumps and systems 2 and 3 have electric motor driven demand pumps. The demand pump supplements the EDP during high demand conditions. All four demand pumps are selected to 'Auto' throughout the flight unless a QRH drill has dictated otherwise. This is standard Boeing procedure and applies to all airlines and all engine types.

Airclues

[QAVION]

"Systems 1 and 4 have air driven demand pumps and systems 2 and 3 have electric motor driven demand pumps."

Actually, this is optional Captain Airclues. Some 747-400 airlines have air-driven demand pumps on all hydraulic systems. Korean Airlines for example. However, I believe the same operating procedures apply (AUTO for landing).

Rgds.
Q.

[Cornish Jack]

Funny old things, the 744 ADPs. Different operating criteria for different power plant. One real oddity which is not mentioned in the basic tech manual is the 'hard-wire' tie-in between the FCUs and the ADPs. Loss of an FCU could affect an associated ADP.
Widebody - There are non-normal conditions in which the switch remains in Auto - e.g. Eng failure and EDP failure.

[747FOCAL]

Would any of the airlines have a standard procedure of switching the ADP to "ON" during Approach? Takeoff?

[QAVION]

"Loss of an FCU could affect an associated ADP."

We're not referring the the 747-400 lavatory "FCU" (Flush Control Unit) here, are we CJ? <img src="confused.gif" border="0">

I guess, not... I don't think there's a link between these and the ADP's... Unless (using a bit of poetic licence here )....

Person flushes toilet during flap retraction, activating the electric blowers for the toilet vacuum system. The engine spools up to compensate for the extra draw on the electrical generators, momentarily increasing the output of the engine bleed air system which causes the ADP to run faster.... :)

Cheers.
Q.

[Intruder]

When in Auto, the ADPs are turned ON automatically when the flaps are extended.

[747FOCAL]

Would you pilots have a problem with turning them to off once the gear and flaps are down? Probably not in case of go around I am betting.

[Cornish Jack]

Qavion
No, no....nowt to do with the 'dunnies'. The Flap Control Units are (rather oddly) hardwired to control particular ADPs - from memory, Left (or No 1)FCU to the No 1 ADP and Right (or No 3) to the No 4 ADP. Soooooo ..(for example) if you have a Left FCU failure, the No 1 ADP won't be commanded to run at Flap selection. This is noted in the MEL relief for despatch with FCU failure, where the related ADP must be switched to ON, not AUTO, for Take-off and Landing.

[Intruder]

747Focal:

Why would I want to turn off the ADPs? I don't selectively turn off any other backup systems! They backup the EDPs for the center autopilot, normal braking, autobrakes, antiskid, and nosewheel steering on approach and landing. With the engine at idle, the EDP alone is insufficient to maintain full pressure under even moderate hydraulic load.

Also, in the event of go-around, landing gear and flap retraction may be compromised, becoming a safety risk.

[747FOCAL]

If you read back at some of the other posts not mine you might be able to figure out why I am asking and what it means to you guys.

Thanks for the posts. You all have been helpful.

[Intruder]

I happened to have seen the first message or 2 regarding 747 approaches into LHR in another forum. However, you cannot assume that all those who post here also read all the posts in all the conferences.

If the ADPs are considered a significant source of noise on one of the quietest airplanes around, and someone is suggesting they be turned off on approach -- one of the most critical phases of flight -- then those people need to re-examine what has gone into attaining the level of aircraft safety we have now!

A couple years ago our airline found a very high correlation between the rate of tire failures on our 747-200 fleet and the use of flaps 25 for landing. Our -400 fleet has always used flaps 30. To prevent a tire failure and its possible consequences, ANYONE should accept another decibel of noise in this context.

[QAVION]

"No, no....nowt to do with the 'dunnies'."

Understood, CJ.... Just a feeble attempt at humour <img src="wink.gif" border="0">

The schematics (for our RR-powered aircraft) show the Right FCU inputting into the HYDIM to start up the #1 ADP when the flaps are in transit....and the Left FCU inputting into the HYDIM (different circuit board) to start up the #4 ADP with the flaps in transit.

Most CF6-powered aircraft seem to have the additional logic to run the ADP's when the flaps are also "out of up".

As you say, it's interesting to note that a particular FCU controls a particular ADP. Normally, if a particular FCU fails to perform its duties another will take over. If that fails, the third FCU will take over (but if the FCU's are hardwired to the ADP controls, then this is of concern).

Cheers.
Q.

[Cornish Jack]

G'day again Q
Yes, I got the funny intent - just didn't put the appropriate smileys in the reply <img src="smile.gif" border="0"> <img src="smile.gif" border="0">
You are probably aware of the other peculiarities of the FCUs in that they don't act quite like the usual triplex redundant systems. The 'normal' condition has TWO FCUs operating (one controlling and the other taking care of display output). If there is then a failure, the remaining one of the two takes over the whole shooting match and if that subsequently fails, No 3 steps in. Not quite what one would expect ! Why??? <img src="confused.gif" border="0"> ...give in. Probably seemed like a good idea at the time. :)

[747FOCAL]

The logic for RR vs GE and Pratt is different. And once on the RR powered 747s ADPs stay on until reset from the cockpit. No I am not suggesting turning them to off you would never make a go around with engine failure.

They are noisy but do not show up in the noise foot print.

[Ford Airlane]

I do not wish to unnecessarily discredit someone based on my feeble knowledge of noise abatement, but I cannot imagine the flaps and demand pumps contribute in anything more than a miniscule way to the noise an aircraft makes.

The noise comes from the engines. Even the airflow over the flaps could not possibly compare to the noise generated by the engines.

As a simple example, I saw the space shuttle take off and land once in Florida. Take-off was noisy because of the engines. Landing was very quiet (apart from the two sonic booms!!), because it was gliding.

Am I missing something?

<img src="confused.gif" border="0">

[Checkboard]

As noise as we hear it is an amplitude modulated wave, then all noise is additive - any monor hum, buzz or whatever will be heard in addition to the moise of the engines, although it may not be load enough to be individually distinguishable.

As to whether flap noise is above the human threshold of perception - listen to a 146 retract the flaps sometime!

[747FOCAL]

A 747 on approach without engines on will ring about 101.5 dB from airframe noise alone and it is the flaps that make the most of it on a 747.