B747 Back up Hydraulics
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.
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.
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There is no possibility of any 115VAC with engs windmilling.
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
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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.
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.
Usual disclaimers apply!
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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.
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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.
All of this is of course IIRC and old age.
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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.
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Sorry guys but the A/C pumps were on system 1 for braking and system 4 for steering
I believe the start logic can be fooled by pulling a certain air-ground system circuit breaker
Last edited by spannersatcx; 30th Sep 2008 at 21:24.
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.
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.
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am aware of only 1 case of a 2-system hydraulic failure on a 747, and no cases of a complete, 4-system failure.
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.
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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.
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.
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classic Hyd
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.
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.
Last edited by Earl; 1st Oct 2008 at 04:40.
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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.
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.
Last edited by Earl; 1st Oct 2008 at 04:19.
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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.
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.
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Flaps 10 would have not given them a takeoff warning.
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...
If all three generators trip offline, RAT extends automatically...a nice safety feature.
Usual disclaimers apply!
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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)
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)
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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.
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.