B747 Back up Hydraulics

[c130jage]

I have been asked the questions as to how a 747 can get hydraulics whilst all 4 engine are out in flight. I refer to the Jakarta incdent, I know Airbus aircraft have a RAT which provides a minimal pressure to power flight controls, but have no experience of Boeing aircraft. Can you help.

[411A]

I suspect Rainboe forgot about a couple of AC powered electric pumps.

Anyway, the original B747 was certainly not fool-proof with regard to hydraulics.
Witness JAL with all fluid loss.
There was only one first generation wide-body jet airliner that had hydraulic fusing as part of the original design (not added on, later)....the Lockheed L1011.
And yes, it has, just like the B747, four separate hydraulic systems.
A superb design.:ok:

[c130jage]

Thanks Guys, That resoves the question.

[Intruder]

Electric vs air-driven pumps were/are options on the 747. All our Classics have 4 air-driven pumps. Our 744s have 2 air-driven and 2 electric pumps.

[Deltabravowhiskey]

Classics, the #4 has an additional electric hydraulic pump used for Push/Tow operations, some versions had a #1 electric as well.

DBW

[spannersatcx]

not sure there will be enough wiggly amps to power AC electric pumps with all engines windmilling.:eek:

[vs69]

In addition to the 4 Engine driven pumps there are ADP's on systems 1 and 4 as they are heaviest users, AC motor pumps on 2 and 3 plus additional auxiliary ACMP on system 4 for braking when under tow/maint operations and as an option on system 1 for steering (these are powered by the ground handling bus though so will not be available in flight) slight drift from the original post I think but hopefully informative!

[junior_man]

And the 747-8 will have a RAT too

[411A]

And the 747-8 will have a RAT too

Just like the L1011, many years before.
Of course, one can then mention hydraulic power transfer units....:D

[SNS3Guppy]

In addition to the 4 Engine driven pumps there are ADP's on systems 1 and 4 as they are heaviest users, AC motor pumps on 2 and 3 plus additional auxiliary ACMP on system 4 for braking when under tow/maint operations and as an option on system 1 for steering (these are powered by the ground handling bus though so will not be available in flight) slight drift from the original post I think but hopefully informative!


Each engine has an engine driven hydraulic pump, or EDP. Each hydraulic system has an Air Driven Pump, or ADP. Standard is one electric hydraulic pump, or ACP, on system 4, and many airplanes have a system 1 ACP, as well.

You're correct that the electric ACP pumps powered through the ground handling bus, and therefore not available in flight.

Systems 2 and 3 do not have standard electric hydraulic pumps.

160 KIAS is the minimum windmilling speed, and this is for hydraulics. It has nothing to do with electrical power. It also does not permit use of gear or flaps, hydraulically.

[gas path]

Of course, one can then mention hydraulic power transfer units
...........that the original 747 classic also had!
Now I'm showing my age:(

Trapped 3 sys. fluid in a closed loop through a PTU operated by no. 4 system return pressure to operate the stab. IIRC.

[FlyingSpanner]

GULP!!

have to say that I have forgotten about any sort of PTU on the classic 747. Then again I did do the engineering course back in 1994 which was not yesterday!!!

However regards to the B744, yes as Rainbow said the AC pumps on systems 2 and 3 are options. If you look at MAS B744's (basic configuration) they have 4 ADP's across the ship. Took me by surprise first time I saw it as I had done the BA differences course from the classic.

Hope that this helps.

Flying Spanner :ok: :ok:

[spannersatKL]

Gas Path..correct.....you are probably the same age as me!! Look in D. P. Davis' book Handling the Big Jets the schematic is in there......though he even mentions the 'Load Evener' system originally fitted to the Wing Gears and not used in service to my knowledge...Agree a brilliant aircraft :ok: and a pleasure to work on....Unlike the torture endured by those of us who tried to keep in the air a certain 3 engined, 4 hyd system wide body previously mentioned!!! :}

I believe the 'Standard' 4 EDP/4ADP/1ACP pump distribution on the Classic became a 4 EDP/2ADP and 2 Electric Pump/1ACP system on the -400...progress, and 2 and 3 systems of course do not really need the 37 gallons a minute 'flow' of the EDP/ADP.

[spannersatKL]

Flying SPanner ....it would have been removed around 1970 during development of the aircraft........

[411A]

Unlike the torture endured by those of us who tried to keep in the air a certain 3 engined, 4 hyd system wide body previously mentioned!!!


Ah, but the pilots loved it...and still do.:ok::}

[Swedish Steve]

However regards to the B744, yes as Rainbow said the AC pumps on systems 2 and 3 are options. If you look at MAS B744's (basic configuration) they have 4 ADP's across the ship. Took me by surprise first time I saw it as I had done the BA differences course from the classic.

If by MAS you mean Malaysia Airlines, their B744 have ACMP as demand pumps in sys 2 and 3. Just went out and tryed it. APU off, 2 and 3 pressurise the hyds, so the AMM must be right.

[Willit Run]

744's were delivered with the #2&3 back up hydraulic systems with either air driven pumps or AC powered electric pumps. Twas an operator option. So, you never really know what your gonna have untill you climb in one.

We had a saying, our fleet was standard until we got the second airplane.
Obviously, we are talking about the used market.

The newest plane I have flown was the Tristar and at the time it was 10 or 12 years old. and that was 8 years ago!

[411A]

The newest plane I have flown was the Tristar and at the time it was 10 or 12 years old. and that was 8 years ago!

You should have flown 'em directly from the factory...what a joy.:ok:
Even today, a nice aeroplane, although getting old...just like yours truly.:}

[HURZ]

I was told by on of our big men that the 747-800 will have a RAT. Boeing and the FAA obviosly just "forgot" to have a RAT installed on the previous 747s.

Everything gets better now...:}

[dream747]

May I ask a few questions regarding the pumps... :}

How and where does the ADP get it's source of air from? Directly from the engine bleed air?

Should all the 4 engines decide to quit would there still be a source of electrical power without having the batteries to come online since the AC motors are powered by EDPs (if I remember reading it this way!)?

Cheers... and as usual, thanks to all! :}

[EHRD-0624]

Funny everybody always mentions the BA and KL encounters with vulcanic ashes but total silence on SQ. They encountered a similar engine out situation somewhere over Indonesia on a B742 and managed to get it safely down at Jakarta on not more than one and a bit despite zero forward visibility due to grit-blasting of cockpit windows, poor weather conditions (rain and moderate crosswind) and ILS u/s.

[glhcarl]

Funny everybody always mentions the BA and KL encounters with vulcanic ashes but total silence on SQ. They encountered a similar engine out situation somewhere over Indonesia on a B742 and managed to get it safely down at Jakarta on not more than one and a bit despite zero forward visibility due to grit-blasting of cockpit windows, poor weather conditions (rain and moderate crosswind) and ILS u/s.

An other phenomenon that was attributed to volcanic eruptions was the crazing of the cabin windows. Thousands where having to be changed prematurity. There was a large study done in the 80's of the problem and was traced to the the acidity of the volcanic ash. Corrective action was to throughly wash windows of aircraft that flew through volcanic clouds.

[SNS3Guppy]

A crazed cabin window is the least of concerns when flying through volcanic ash.

An older technique for a volcanic ash encounter involved use of the Overheat Test button on the window heat panel, to shatter the outer panes of the forward cockpit windows to restore some visbility after being damaged by volcanic ash.

That had no effect on the cabin windows of course...but cabin windows are far down the priority chain if a volcanic ash encounter has occured.

[spannersatcx]

How and where does the ADP get it's source of air from? Directly from the engine bleed air? From the bleed air manifold, so you can still use the ADP even if the associated engine is not running, or from the APU.

Remember these ADP's are demand pumps and only cut in when the EDP can not supply enough pressure, normally in high work load situations, gear/flaps etc etc.


since the AC motors are powered by EDPs (if I remember reading it this way!)? I presume you are talking about the AC demand/aux pumps. EDP's running or not (Engine Driven Hydraulic Pump) has no bearing on AC generation at all.

[SNS3Guppy]

Remember these ADP's are demand pumps and only cut in when the EDP can not supply enough pressure, normally in high work load situations, gear/flaps etc etc.


When selected to AUTO, yes. When selected to CONTINUOUS, no.

Should all the 4 engines decide to quit would there still be a source of electrical power without having the batteries to come online since the AC motors are powered by EDPs (if I remember reading it this way!)?


The batteries are already online, and in absence of generator power, external power, or APU generator power, are the sole source of electricity.

At this stage one is down to standby power, with few items powered off the standby bus, and a short time to enjoy it.

EDP's are engine-driven hydraulic pumps, and don't power anything with electricity, as they only pump hydraulic fluid.

AC motors, or the AC hydraulic pumps, are powered by electricity...but have nothing to do with the engine driven pumps. The electric hydraulic pumps, one on number 4 system and sometimes one on number 2, provide supplementary hydraulic pressure for ground operations, such as towing and powering body gear steering (hydraulic system No. 1) and for applying the parking brake (hyd system No. 4).

[glhcarl]

A crazed cabin window is the least of concerns when flying through volcanic ash.

An older technique for a volcanic ash encounter involved use of the Overheat Test button on the window heat panel, to shatter the outer panes of the forward cockpit windows to restore some visbility after being damaged by volcanic ash.

That had no effect on the cabin windows of course...but cabin windows are far down the priority chain if a volcanic ash encounter

The cabin windows crazing didn't happen immeditely while flying throught the volcanic ash cloud. The window crazing shows up weeks or months later. If it was not addressed the outer panes would fail. So to prevent failures aircraft that were exposed to the ash cloud would have all the cabin windows changed. When a operator has to replace more than 100 windows at $300 per window it becomes a real concern.

[NSEU]

How and where does the ADP get it's source of air from? Directly from the engine bleed air?

In the air, engine bleed is the only source of air... unless you left the APU running after starting it on the ground (and were below a certain altitude... the APU runs out of "steam" at higher altitudes)

Should all the 4 engines decide to quit would there still be a source of electrical power without having the batteries to come online since the AC motors are powered by EDPs (if I remember reading it this way!)?

To get any electric powered hydraulic pumps to operate in the air, you need the engines to windmill fast enough so that the high speed rotor (N2 or N3) is above 50%. Engine electrical generators do not operate below this speed.

Electric pumps on #2 and #3 maybe be considered optional.. but there is a lot of aircraft flying around with this option. I wouldn't be surprised if the electric versions outnumber the non-electric ones.
Note that you still need main bus electrics to control the air-driven pumps, so, again, windmilling speed is a factor.

Rgds.
NSEU

[dream747]

Thanks for the clarifications!

Sorry if I sound confused, what about the primary source of power for the alternators to power the electric demands of the airplane? Does this come from the engine?

[BelArgUSA]

In simple words -
The 747 have 4 electrical generators (1 per engine).
They produce alternating current 115V/400Hz and each are 60 KVA of power.
The APU is also equipped of 1 or (option) 2 same generators (for ground use).
The 747 Classic APU cannot be used in flight to produce electricity.
DC (28V) is produced by 4 transformers rectifiers which change the 115V current.
A small aircraft battery stores 24V DC for emergency use.
Another similar battery stores 24V DC to start the APU.
xxx
:)
Happy contrails

[gas path]

The APU is also equipped of 1 or (option) 2 same generators (for ground use).....although rated at 90kva due to better cooling :8
HEY! how did we get from backup hydraulics to window crazing and now electrics :confused::}

[SNS3Guppy]

To get any electric powered hydraulic pumps to operate in the air, you need the engines to windmill fast enough so that the high speed rotor (N2 or N3) is above 50%. Engine electrical generators do not operate below this speed.


You're talking about the -400, then?

This isn't possible on the Classic, as the electricl pumps can't be powered in flight, nor can electricity be obtained from windmilling powerplants...it's hydraulics only with a minimum mindmilling speed of 160 KIAS, and no normal gear or flaps.

[Intruder]

There is a lot of confusing information being posted here.

It is impossible to windmill an engine fast enough to run the generator or to supply sufficient bleed air to run a hydraulic demand pump. ONLY the engine-driven pump will work when the engine is windmilling, and ONLY above approx 160 KIAS.

After the APU is shut down, it cannot (-400) or shall not (Classic) be restarted while airborne, so it is not an option for an airborne hydraulic failure. The APU generators shall not be used airborne.

While the Classic has 4 air-driven demand pumps (1 per engine/system) in addition to the engine-driven pumps, the -400 is available in several optional configurations where 1 or 2 of the air-driven demand pumps is replaced by an electrical pump. The air-driven pumps require bleed air from at least 1 running engine connected to the bleed-air manifold, and the electrical pumps will run (as selected/required) as long as there is at least 1 engine running and its generator is powering the synch bus.

The electrical Aux pump on system 4 runs ONLY on the ground, and cannot be run airborne (except in some cases of failed air/ground switch logic). It is sized to charge the parking brake accumulator ONLY, and will not reliably run ANY other hydraulic system.

I am aware of only 1 case of a 2-system hydraulic failure on a 747, and no cases of a complete, 4-system failure. While the 747-8 may have a RAT, I don't know why anyone thinks it necessary for hydraulic power (though it would be nice for emergency electrical power).

[SNS3Guppy]

After the APU is shut down, it cannot (-400) or shall not (Classic) be restarted while airborne, so it is not an option for an airborne hydraulic failure.


Not necessarily. Some APU installations permit airborne operation, and some don't. Where the APU in flight operation is permitted, it's restricted to 15,000'.

[Willit Run]

Intruder,
Wasn't the JAL crash many years ago a result of all four hyd. systems being severed when the pressure bulkhead came apart?

[BelArgUSA]

JAL 123 was the flight - mid 1980s. Over 500 victims.
Loss of the 4 hydraulic systems, because faulty repair of aft pressure bulkhead.
No hydraulics = loss of all flight controls.
xxx
:{
Was not a happy contrails day...

[Intruder]

It is possible that total hydraulic failure was named as the proximate cause of the JAL crash. However, that was, as you said, a catastrophic airframe failure that in turn caused the other failures. There was NOTHING that another hydraulic pump or RAT could have done in that situation.

[Earl]

Some 747 classics have a electric pump for number 1 system also, I think the old JAL classics had this and a few others.
Both the number 1 and number 4 electric pumps get there power from the ground handling bus and cannot be powered in flight.

[411A]

There was NOTHING that another hydraulic pump or RAT could have done in that situation.

While this is true, there remains one other safety feature that was fitted to only one type of first generation wide body jet transport, originally, from the factory (not added later).
Hydraulic fusing.
The type?
TriStar.
A superb example of aircraft systems redundancy...bar none.

[Dan Winterland]

Thought it would be the Tristar!

On my current type, the manuals state that Hyd power is available from a windmilling engine, but with no guidance as to what speed that is. The simulator gives us a warning of low Hyd press at around 130 kts if the PTU isn't operating. But a mate who had an engine failure for real one day said the windmilling engine kept of generating enough Hyd pressure down to about 40 knots. They didn't get a warning until they were turning off the runway!

[Old Fella]

Four hydraulic systems, RAT, spacious cockpit, superb autopilot and autoland system. Never had the pleasure of a -524 powered variant, but it must have been an improvement on the -22B. Still the only aircraft to use DLC to my knowledge and it was a pleasure to crew.

[mustafagander]

To stick to the topic.

The B747 WILL have 3000psi with all engs windmilling down to about 160kts.

There is no possibility of any 115VAC with engs windmilling.

There is no possibility of any ADP with engs windmilling.

Gear and flaps will be available, albeit at reduced rates, with all engs windmilling. This will not result in loss of control - system 2 & 3 hydraulics can handle flight controls while systems 1 & 4 are busy.

[NSEU]

There is no possibility of any 115VAC with engs windmilling.

Well, I hate to burst the bubble....

A 744 pilot was telling me recently that he lost an engine in cruise. However, at cruise speeds, his dead engine was windmilling fast enough to produce 115Vac. He even said it took them a while to realise that they had actually lost an engine, because everything was working "normally" (he said).

I believe this was one of the interesting discoveries when BA's 747 engines flamed out with volcanic ash... They were getting a lot more electricity than was reproduced in their company's simulators... which told them they should only be getting Standby Power.

To the gentleman/men who were asking earlier, yes, I was referring to the so-called "optional" electric pumps on #2 and #3 systems on the 744, not the 747 which has only air-driven pumps available in the air.

Some 744 electrical bus control units have logic which allows the APU generators to come online even in the air if all four engine generators have died. However, the APU needs to be running prior to takeoff.

(Sidenote) I believe the start logic can be fooled by pulling a certain air-ground system circuit breaker (not all), but this is well outside the realm of standard operating procedures. IF you could get the APU started and providing power, AND you had electrics pumps fitted to #2 & #3 hydraulic systems, then you could conceivably power any of the electric pumps, perhaps even the AUX pump/s (as the aircraft thinks it is on the ground).... BUT, what is the point, when you should have sufficient hydraulics for flight control from windmilling engines.

Rgds.
NSEU

[SNS3Guppy]

Gear and flaps will be available, albeit at reduced rates, with all engs windmilling. This will not result in loss of control - system 2 & 3 hydraulics can handle flight controls while systems 1 & 4 are busy.


Again, perhaps you're talking about the 744, because the Classic's procedures are clear; do not use gear or flaps with windmilling hydraulics. The demand is great enough with gear that additional augmentation is required with the ADP. For that reason, with windmilling engines, hydraulic extention of gear or flaps will not be available.

Our procedure very clearly states "Do not operate flaps or gear."

If gear or flap operation is necessary, there's always alternate extention. There's obviously very little electricity available to do that, and it's not available for long.

[gas path]

JFI we use the aux. pumps during maintenance and they will quite nicely operate the gear and flaps, albeit not together. Due to the flow rate they are slow but are very useful to assist with rigging and/or leak checks. The only time they complain is on gear lowering when the pumps cannot keep up the flow rate as the legs freefall, so the legs will starts to 'bounce'. A bit disconcerting! For that reason its one leg at a time then there is not a problem.:8

[matkat]

Sorry guys but the A/C pumps were on system 1 for braking and system 4 for steering some aircraft also had an option of an ACP on system 2 also for brakes in the event of the #1 failing but you had to open the system via a spring guarded switch in front of the Capts control column.
All of this is of course IIRC and old age.:}

[SNS3Guppy]

JFI we use the aux. pumps during maintenance and they will quite nicely operate the gear and flaps, albeit not together. Due to the flow rate they are slow but are very useful to assist with rigging and/or leak checks. The only time they complain is on gear lowering when the pumps cannot keep up the flow rate as the legs freefall, so the legs will starts to 'bounce'. A bit disconcerting! For that reason its one leg at a time then there is not a problem.


Not an option in flight, of course.

[c130jage]

Sometimes you just wish you had not asked a question to start a thread !!!
I must admit it makes interesting reading though/
Thanks to all for the responses

[spannersatcx]

Sorry guys but the A/C pumps were on system 1 for braking and system 4 for steering Wrong way round, 4 for brakes 1 for steering.

I believe the start logic can be fooled by pulling a certain air-ground system circuit breaker You can trick it to simulate airmode when on the ground by pulling cb's it's a bit more difficult to trick it to groundmode when in the air, it takes a bit more than pulling cb's, we used to do it when on jacks in a hangar.

[mustafagander]

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.

Guppy,

I'm not talking about procedures, I'm talking about what is possible.

[TowerDog]

am aware of only 1 case of a 2-system hydraulic failure on a 747, and no cases of a complete, 4-system failure.

Then there was the Pan-Am 747 that lost 3 hydraulic systems on take-off, came back and landed and the whole thing was captured on film.
With only 1 system he did not have quite enough elevators to flare and hit pretty hard, bounced and came back down in one piece.

After shutting down, the airplane tipped over on the tail as the body-gear was still retracted.

[411A]

Then there was the Pan-Am 747 that lost 3 hydraulic systems on take-off, came back and landed and the whole thing was captured on film.

Ex-SFO, departure on runway 01L.
Hit approach lights at the far end.
Flaps 10 takeoff instead of the required flaps 20.
Right after this, PanAmerican added, right at the end of their before takeoff check...a configuration check, flaps, spoilers, stab trim.

[Earl]

Brakes can be selected to system 1 on the F/E panel if needed.
But you need to make sure that you have accumulator pressure showing in the brake pressure gauge.
If not and you shift system 4 to system 1 then you will lose system 1 also as it will be dumped out through system 4.
This will then give you a dual hydraulic failure.
On a normal operation system 4 powers the brakes and everything on the outside, meaning brakes, wing gear and outboard flaps.
System 1 everything on what we call the inside, body gear, nose wheel steering and the inboard flaps.
If 1 and 4 are gone then the gear can be lowered manually with the switches on the overhead panel, just the gear doors remain open as no hyd to close them.
Brakes will then be the reserve brakes which operates off system 2.
But once parked pressure has to be maintained to system 2 as there is no accumulator and once the engines are shut down then the parking brake becomes another problem, this can be accomplished with the apu air and the system 2 ADP until chocked.
Also some other anti skid sensing issues when using system 2 brakes.
There are also some 747 classics that can use the apu air source in flight, this is usually shown with a placard above the apu panel.
But I have never seen one that allowed you to use the APU electrics as for one it would never parallel with the engine driven generators.
Two it is in the manuals as forbidden.
Now if you lost all engine driven generators would it work, maybe.
But no procedure for it.
Someone want to expand on this feel free.
Starting to sound like a recurrent here, sorry.
Hope this helps.

[Earl]

411A,
Flaps 10 would have not given them a takeoff warning.
1.Takeoff warning is Leading edge flaps extended.
2. Trailing edge flaps takeoff position, either 10 or 20.
3. Spoilers armed.
4. Body gear steering centered.
5. Stab trim in the green range.
Advancing the throttles to takeoff thrust with the number 3 being the one that triggered the warning, flaps 10 would have been sensed as ok and no takeoff warning would be heard.
This is why 2 people check the takeoff data.
Really easy to be on the wrong chart.
If we were all perfect we would not be in this job, ha ha.

[SNS3Guppy]

Guppy,

I'm not talking about procedures, I'm talking about what is possible.


Say again?

[Earl]

As for the aircraft that have the rat it is only effective with the airspeed.
747 classic has no Rat.
Forgot the numbers for the Tristar but do know with the airbus 300 its useless below 130 kts.
Would be on the ground then anyway.

[411A]

Flaps 10 would have not given them a takeoff warning.


Many differences with PanAmerican 747 aircraft, just as with their 707 airplanes, before.
Customer option, originally.
In the SFO case, a change of runway at the last minute.
Takeoff planned on the longer runway (flaps 10), but flaps 20 needed on the shorter runway, due to TOW.
A rather big wake-up call for PanAm, at the time, hence the configuration check prior to departure, to be sure that the correct flap selection was made.

I knew the Chief Pilot, Pacific at the time, nice guy.

Forgot the numbers for the Tristar...

160 knots, minimum, powers B system only.
If all three generators trip offline, RAT extends automatically...a nice safety feature.

[mustafagander]

Guppy,

From post 46. It is possible to extend SAFELY gear and flaps with 4 engs windmilling. I agree that it may not be an approved procedure in your airline.

[SNS3Guppy]

If you say so.

[gas path]

Hydraulic fuses fitted to all the brake lines at the A/Skid modules they are there to protect the integrity of the hydraulic systems if a brake line is damaged. They are a simple poppet and spring with a manual reset lever and 'trip' if there is a sudden high flow rate and drop in pressure downstream.
The other hydraulic fuses are there to protect the hydraulic system integrity if the rear pressure bulkhead should fail (JAL 123) these are basically the same except they are self resetting when the pressure either side of the poppet is equal. (+/- 5psi)

[boofhead]

The 744 has a fuse in the #4 hyd system. In the event of a JAL-type incident they would have one elevator, one set of spoilers and whatever else comes from the #4 system. Enough to fly.
There is a kit available to retro-fit the Classics with a fuse, but the cost is high enough that most operators declined to fit it. Criminal, that.
The Classic has an electrical pitch control that only a handful of pilots and flight engineers know about, and few practice with it in the sim, but it does work and I recommend you try it. Never know if you will need it. If the JAL crew had known about it maybe they would not have lost the airplane. Maybe. But most pilots who try it in the sim seem to get back on the ground, maybe not on a runway though. Could be used to put the airplane into a large open area or a lake, and with practice a safe landing on a long runway is feasible. If you understand the Classic system, you can get a similar effect on the 744, using the Standby Flap control, but once again you need to think about it before the emergency happens and practice it in the sim first.

[SNS3Guppy]

The Classic has an electrical pitch control that only a handful of pilots and flight engineers know about, and few practice with it in the sim, but it does work and I recommend you try it. Never know if you will need it.


In the Classic, are you talking about trying to vary pitching using alternate flap extention?

The elevators are powered by hydraulics, with no manual reversion. The stabilizer trim system is powered by hydraulic motors, without an electric reversion. What electric system are you talking about?

Pilot input controls hydraulic actuation of the inboard elevators, and the inboard elevators control the opposite outboard elevator by cable to a hydraulic actuator...There isn't an electric motor to the inboard or outboard elevators, and the motor moving the horizontal stabilizer is composed of two hydraulic motors.

Electric input from the control wheel switches only signals the stabilizer trim drive units to operate, but there's no electricity moving the stab; it's commanding sequence valves for the hydraulic motor to operate, and it's operated hydraulically. Take away the hydraulics and the electric trim switches can be moved all day long, to no avail.

Likewise, the pedestle manual trim levers do nothing more than sequence hydraulic fluid to move the stab trim unit motors, and involve no electrical motors.

With this in mind, how is electric pitch control available? If a trim runway occurs, electrical input to the stab trim can be interrupted by pushing on the control column in the opposite direction of the runaway travel, but the solution there ultimately involves hydraulics, too; the cutaway switches on the pedestle to cut hydraulic power to the hydraulic trim motors. With that cut, or lost...what's left to drive the stab trim unit?

[gas path]

Actually squire boofhead is sort of right! The classics alternate T/E flaps switches IIRC were marked 'pitch up' for the outb'd and 'pitch down' for the inb'd, so I guess there would be a pitch change albeit extremely slow. However whether it would have been useful or not if used in anger I don't know.
Or indeed if the alternate motors lasted long enough, they don't take too kindly to being run up and down continiously.:8

[SNS3Guppy]

I imagine that in extremely calm conditions, the alternate flap switches could be used to effect pitch change, though that might make for an interesting approach and landing. Travel on the normal flaps takes about 45 seconds. Go to the alternate switches, and the rate is greatly reduced; full travel takes five and a half minutes. That's a little long to be making corrections while flying an approach. Certainly if it's all you've got, it's all you've got...but you're going to get faster changes by trimming for a speed and using power.

Further, if you do indeed have a full hydraulic loss, and power is a big part what you're doing, then you also have no roll control beyond splitting the flaps...again, better hope for a calm day, an extremely long runway and very uniform engine response.

[BelArgUSA]

In the 707, we had an alternate procedure extending inboard flaps to get the nose up, or extending outboard flaps to get nose down in case of trim problems. Panel overhead captain's head was even indicating what switch to use. Also we could use partial spoilers, inboards or outboards. Although such procedure does not exist in 747, it could be achieved. I will play that game in a simulator one of these days, to see what can be done.
xxx
After all a 747 is just a big 707 with a lot of extra goodies.
xxx
:8
Happy contrails

[spannersatcx]

I would be climbing into the roof space with the crash axe Trouble is they've removed the crash axes from out 747/744:eek:

[SNS3Guppy]

But before I did, I would be climbing into the roof space with the crash axe and trying to pull those bloody control cables with my asbestos gloved hands until I got the right one!


If you're talking about a hydraulic loss, what those "bloody control cables" would be doing is...nothing. They only port hydraulic fluid to actuators...and without any fluid, you'd be doing nothing more than what you're doing with the control column...nothing.

[boofhead]

Al Haynes could have used this system in the DC10 except that that airplane does not have the electric backup to the flap. One point of the Boeing system is that an airplane will fly the speed at which the failure occurred, unless you can change the trim setting somehow. The DC10 did not have that option, but the 747 Classic does. As the flap is extended, the trim speed reduces. As the gear etc is moved, the trim speed can be changed to adapt by extending the inboard or outboard flaps accordingly. With engine power to assist in turns, rate of descent and speed adjustments, it is possible to set up a slow approach with flap set and by moving one set of flaps to even maintain a glidepath. It is an exercise you can try in the sim. Turbulence would be a bad thing, but still better than just sitting there on your hands.
One note of warning; do not pulll the throttles closed for the touchdown, or else the airplane will nose in. Wait until you are on the ground.
In the 744 you can achieve the same effect by pulling either the inboard or outboard flap circuit breaker (just behind the FO seat) and extend or retract one set to achieve the same thing, but with a hydraulic fuse, that should not be necessary.
I remember wondering out loud why those arrows showing the trim change were on the electric switches for the alternate flap in the Classic and was lucky enough to be flying with a smart South African fellow who explained it all to me. He said they used to include it in the type rating courses but dropped it when told the chance of such a failure was so low. A few hundred people might, if they were able, correct that opinion.

[411A]

Al Haynes could have used this system in the DC10 ...

If Al Haynes had been in an L1011 instead of a DC-10, he would have had a much better chance of landing the airplane in one piece...due to hydraulic fusing...built in at the factory, not added later on.:cool:
Face it folks, the 'ole TriStar was so far ahead of its time, it's unreal.
Speaking with a (now) retired Boeing design engineer a few months ago, he related that when Boeing looked at the L1011 years ago, they found the systems integration/redundancy so very good, it was a huge wake-up call to the folks in Seattle.
Lockheed, simply the finest, straight out of the factory, years ago.:ok:

PS: and yes, one can split the spoilers for pitch control, just like on the 707, years before.
A superb design.

[dream747]

Hey all couldn't resist this post. I don't have the wealth of knowledge to add to this post - I'm just a professional pilot wannabe.

But I really enjoyed learning in this post. Thanks for sharing everyone!

[TowerDog]

If Al Haynes had been in an L1011 instead of a DC-10, he would have had a much better chance of landing the airplane in one piece...

Okay, but what about the L-10 in the everglades?
Superior design, but no autopilot disconnect warning?

Or the L-10 aborting after V-1 in JFK due to false stall warning?


Good bird but not invincible...:rolleyes:

[stilton]

Not fair to blame Easterns L1011 crash on the aircraft really, perhaps there should have been a louder autopilot disconnect warning but what happened to 'FLYING THE AIRCRAFT' someone should have been dedicated to that task exclusively.


And at JFK what kind of Pilot reacts to a stall warning after rotation by PUTTING IT DOWN ON THE RUNWAY ! by any standard that was irrational behaviour to a spurious warning, the aircraft was flying, the only appropriate response would have been to push the power up and lower the nose a tad.


Had the stick shaker go off a few time myself over the years after rotation, not that unusual with gusts or a 'sticky' aoa vane, putting it down again is unthinkable and disastrous in any aircraft.


Ridiculous to blame these accidents (officially attributed to Pilot error) to design deficiencies.


The Tristar never had a design caused accident, quite incredible really, Douglas could have done a lot better.

[gas path]

As good as it was/is didn't an EAL L1011 come very close to a hull loss when the 'fail safe' shaft failed?:ooh: Due in part to a location bearing failure caused by an oil fire inside the LP shaft.
IIRC the fan and shaft assy crawled its way up the 'S' duct and caused the loss of 3 hydraulic systems. I guess in that case the damage was upstream of the hydraulic fuses?
Not long after that a (Fan Catcher) mod. came out. Still it is one damn clever bit of kit...dunno why the RAF make such a meal of it.:E

[411A]

Another 'almost' for the L1011 was over the Arabian Gulf, enroute KHI.
A wheel burst in the wheel well at FL290, ruptured the pressure hull, and disabled three of four hydraulic systems.
The airplane was diverted to DOH, with only system D fluid remaining, and landed very nicely by the First Officer...which was required, due to the Captains pole then being unserviceable.
SV trained for this procedure at each sim detail for F/O's...the quite good training showed when the chips were down.

[Dan Winterland]

The "Pitch Up" and "Pitch Down" indications on the overhead panel on the 74C are reminers as to which way the aerodynamic trim goes when using the Alternate Flap extension. I'm pretty sure the intention wasn't to give the crew an alternate pitch control system. Having used them in the sim, I'm certain that pitch control would be near impossible.

[SNS3Guppy]

I'm not sure how deft one could be with those controls. As stated before, they take over five minutes to move full travel; they're very, very slow. Additionally, per some manuals, they work hard; a 20 minute cooldown period for the motors after having fun full travel. Working them back and forth sounds good on paper and in the simulator...but the airplane isn't the simulator. Imaginary motors in the sim have no duty cycle because they don't exist; real motors burn out, seize, burn brushes, fail where you don't want them to, and may not work out nearly as well as in the simulator.

Remember that for all it's training value, the simulator still pretends to show that which does not exist.

[NSEU]

Additionally, per some manuals, they work hard; a 20 minute cooldown period for the motors after having fun full travel.

Isn't the cooling period only applicable to ground ops? The JAL 747 had the gear down... so plenty of cooling at altitude

[SNS3Guppy]

Gear isn't really applicable to electric flap motors. In fact, the motors are working a lot harder under an airload to move the flaps, than they might on the ground.

I would imagine you would run all flap half way, then you could play with inboards and outboards separately to avoid overheating. If some motors did burn out, hopefully you would still have the other flap sections still working getting pitch up or down on that inboard or outboard section only.


Some motors? There are only two.

The Leading Edge Devices have separate motors for the groups, but for the trailing edge you have a choice; inboard or outboard.

[SNS3Guppy]

I don't know how many motors each flap section has.


Sure you do. I just told you. Two motors; one for in board flaps, one for outboard flaps.

Also although they work hard in the air, with the gear down, cooling is much better.


Why does putting the gear down cool electric flap motors? Further, for a given airspeed, how does the gear have any effect on the load under which the flap motors are operating?

The answer is the same in both cases...no effect.

They'd also not work very hard retracting.


Not so. The load on the torque tubes exists up or down.

Don't you think it would work?


I don't speculate. Has it ever been done before?

[NSEU]

Why does putting the gear down cool electric flap motors?

The flap motors are located in the wheel wells on a 747. Even though 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"

I get the point about increased airloads, though (thanks for the reminder, Guppy)... However, I'm not sure how much they would increase in the flap ranges we are talking about for pitch control. I'd imagine extension would be more in the fore-aft plane, than the up-down plane.

Further, for a given airspeed, how does the gear have any effect on the load under which the flap motors are operating?

Did anyone actually say this?

Rgds.
NSEU

[john_tullamarine]

Not directly pertinent to the present discussion but an interesting observation -

In the early days of CRM work, my airline was a main player in Oz. One of the emergency refresher school exercises for a while involved role play with two people out of each other's sight co-operatively trying to achieve a goal involving difficult communication against the clock. A typical exercise was for one to communicate the arrangement of a set of coloured blocks with a goal that the other should rearrange his/her set to match.

I found it interesting in the extreme that, nearly to a (wo)man, the aircrew folk played it down to the wire. Conversely, the non-aircrew folk tended to "throw in the towel" when it became evident that the clock was likely to win .. think I would rather the former fighting attitude in the cockpit with an unusual, potentially catastrophic failure .. than the fatalism of the latter ?

I'm with Rainboe .. if nothing else at least it fills in the time before you die.

[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" :ugh:

[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. :ugh:

[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]

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