B747 Back up Hydraulics

[SMOC]

As said with no hydraulics the gear would have been lowered by the alternate system, therefore leaving the gear doors open and a hell of a gale blowing around the wheel well, hopefully providing some additional cooling to the electric flap motors to allow you possibly that bit of extra time to get them in the best position to make an approach from. When the chips are down you have to try whatever you can pull from your bag of tricks and not leave it in "the hands of a---h"

[Bullethead]

In a four engined airliner you may also get limited pitch control by using different thrust levels on the inboard engines compared to the outboard engines.

Regards,
BH.

[john_tullamarine]

In a four engined airliner ...

That might be workable at low speed due to nacelle inlet normal forces but how would it work at high speed ?

[SNS3Guppy]

Well yes, it has.

A 747 lacking hydraulics has been flown and landed using alternate flaps for pitch control? Really? Where and when?

The flap motors are located in the wheel wells on a 747. Even thought the larger gear doors reclose after the gear has been extended(normally), there are still big gaps for air to get into the wheel wells. "Wind-chill factor"

Under normal operation the gear doors close, but not in alternate extention, and this is, of course, a thread on loss of hydraulics and back up hydraulics. The gear doors in a situation involving loss of hydraulics would normally be open.

I haven't seen anything stipulating reduced cooling periods with the gear down; apparently Boeing didn't feel this pertinent. Point is, while you may be able to achieve some semblence of a stable descent, trying to fly the airplane around on the alternate flap motors...the ones that take five and a half minutes to move the flaps...is really more of a sim exercise than an alternate way to land the airplane.

Certainly one will try what one can...but to think of it as another way to fly the airplane or to control the airplane is a bit of a stretch.

[Earl]

The lengthy period with alternate flaps is just between flap 1 and 5, the rest of the way is a little slower than normal but not so bad.
Lots of distance to cover between flaps 1 and 5.
The only overheating I have ever seen was from the leading edge flaps using the alternate system.

[NSEU]

Under normal operation the gear doors close, but not in alternate extention, and this is, of course, a thread on loss of hydraulics and back up hydraulics.

Well, actually, it began as thread about the Jakarta incident which involved the loss of engines, but not the loss of all hydraulics. It was hijacked by the JAL incident.

I used the words normally and still to indicate cooling under (semi-)normal circumstances. I expected the experts to fill in the gaps about alternate extension (and the extra cooling) for themselves, not correct me for not doing so.

[spannersatcx]

I've got a little lost somewhere, are we talking 747 classic or -400?
I think it's still about the classic, (I get easily lost) anyway the 25 minute cooling down period is after one full down and one full up cycle. It takes around 6 mins to go from 0 to 30.

If it is the 744 (I don't think it is) then alternate flaps are a completely different kettle of fish.

[BigJoeRice]

"though he even mentions the 'Load Evener' system originally fitted to the Wing Gears and not used in service to my knowledge..."

The 747-100's we operated at TWA in the early 70's had both the load evener system (a most unfortunate concept) and the PTU in the stab bay.

[spannersatKL]

Thanks Big Joe didn't realise the system (load evener) actually entered service though was not there for long! A wonderful aircraft probably the best if you ask me.

(27 years keeping them in the air ...)

[BigJoeRice]

the best if you ask me too..............sorry got all teary eyed.

[BigJoeRice]

The tops of the wing gear and adjacent body gear struts were inter-connected with a two inch(ish) diameter pressure balance line so that excess pressure buildup in one gear on one side during landing and taxi, could be "shared" with the other gear on that side. The line was filled and bled via a service port and I suppose you could think of it as a hydraulic spring. I heard the DC3 has a similar arrangement but don't quote me on that. In service it was found to be unnecessary because the gears worked together just fine and I think it was gone by the time the -200's appeared.

[411A]

heard the DC3 has a similar arrangement but don't quote me on that.

DC-3?
Nope, never heard of it, and I'm rated on the machine.
Now, C-47's for the AAF etc....possible, never flew those.

[Jumbo Driver]

Originally Posted by BigJoeRice

The tops of the wing gear and adjacent body gear struts were inter-connected with a two inch(ish) diameter pressure balance line so that excess pressure buildup in one gear on one side during landing and taxi, could be "shared" with the other gear on that side.

Never heard of it myself and I flew the -100s for about 20 years - but it sounds to me suspiciously like the Hydrolastic suspension found on the ADO16 and the later ADO15 ...


JD

[BigJoeRice]

Jumbo Driver
"Never heard of it myself and I flew the -100s for about 20 years"

Lucky you on both counts.....

411A
"DC-3? Nope, never heard of it, and I'm rated on the machine".

It was a folk tale doing the rounds at TWA back in the day; perhaps propaganda by somebody trying to justify it. Thanks for putting that one to bed.

[SNS3Guppy]

Guppy, you normally write extremely long, readable and informative contributions here, but I can't help feeling you are not fully understanding what this is about. Have you flown 747? What I'm saying is the 747 Alternate or Reserve flaps (I can't properly remember what they were called, it was 4 types ago) have been electrically operated in the air, and medium trim changes occurred due to location of the flaps- they give you an element of pitch control. The electric motors are designed to get the flaps to move slowly, but we are discussing the case when all 4 hydraulics are gone, the control column is waggling back and forwards to no effect, I have carved my way into the roof void and played trapeziums like a monkey on the control runs to no effect (bit of a waste of time that one!), and we are now back in the seat watching awful phugoids expanding each cycle, and we're thinking 'well, better not play with the emergency flap motors because they might burn out?' Why do you not think it would work? Most technically literate 747 pilots have the knowledge that it is available as a last resort.

I currently fly the 747, yes. And no...no 747 has ever been successfully flown, much less landed, following loss of all four hydraulic systems, using the alternate trailing edge flaps.

Why do I think it would not work? You already asked me if I thought it would work, and I replied that I would not speculate. Why do you keep asking the same question? Your question is asked and answered. Move on.

We're thinking 'well, better not play with the emergency flap motors because they might burn out, are we? Doubtful. However, do you suppose the trailing edge alternate flaps, which take 5-6 minutes to run full cycle, are up for flying the airplane with continuous inputs as required, for the duration of the time period necessary to fly to, reach, and operate the airplane on an approach to a landing? Again...it hasn't been done. Perhaps it might work, perhaps not...and certainly one will try everything one can...but to think of it as an alternate means of controlling the airplane following loss of hydraulics would be in error. It's not intended for that, it's not designed for that, it's not a procedure in our manuals for that, or taught for that...it falls more in the same category as a opening the doors in a cessna 150 to effect a turn...it might work, but it's ancillary to the purpose of the control and a coincidence if it does. The alternate flaps control is not an alternate pitch mechanism. The airplane has no reversionary control or electrical ancillary control, and the intended protection is redundancy, not electrical alternate trailing edge flaps.

[NSEU]

Over the years on B747 100, 200, 300, 400 & SP I have been involved in shutting down 5 engines, 4 RR & 1 GE. Even on the SP which as you no doubt recall was kinda fast in crz, the A/C gen went off line rapidly.

I find your friend's claims about A/C gens remaining on line with the engine shut down unsupportable from my own personal observation. Not theory, observation.

Mustavagander, I believe you, but my 744 pilot friend has restated that his generators stayed online (on two occasions). Not sure what engine he has on his aircraft though... Maybe he has P&W.

I'll keep digging.

Rgds.
NSEU