B747 onboard systems
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B747 onboard systems
Hi, I am reading PMDG's operating manual for their B747.
I am at the chapter about aircraft systems and since I am a bit more interested in engineering and since the PMGD manual are not very detailed and in some chapters the manual has huge gap or the explanation isn't really understandable I am asking those on this forum who are experts when come to aircraft technics.
HYDRAULIC SYSTEM
Manual says that B747 has 4 independant hydraulic systems. It has 4 engine driven demand pumps (one per engine), 4 hydraulic reservoars and 4 air driven pumps. Then it says that engine 4 has also AC electric driven AUX hydraulic pump - used only to power brakes durring ground towing usage. Then in the next statement it comes to a bit contradictious statement with previous one (each engine has air driven pump) as manual says that engine 1 and 4 have bleed air driven AUX hydraulic pump and engine 2 and 3 have AC electric driven AUX hydraulic pump.
Logicaly stated I'll say that there are 4 engine driven pumps, 4 AUX pumps (bleed air driven in engine 1,4 and AC driven in engine 2,3) + additionaly AC driven AUX pump for brakes.
Now I don't know if APU has aslo mechanicaly driven hydraulic pump, but I gues that it can run anyone of four engine AUX pumps via bleed air or AC electric (in case all four engines are malfunctioning).
ELECTRICAL SYSTEM
Manual says that each engine has 115V, 400Hz, 90kVA AC generator driven via constant speed drive, and all four generators can be paralled if they all works well (providing 400Hz). Then there are additional 2 AC generators driven by APU of the same characteristics as those on engines, but they aren't paralled. Then manual says there are also 2 nickel-cadmiun batterys onboard and if I understood they can only be charged via external power source. But on the next side manual says that there are 4 battery busses. Then manual says that there are automatic SSB that split left/right side of the plane (this is needed if sides are not powered via paralled generators).
What I don't know here how many batterys are on board and what they can power (manual says all standbay systems). I predicts that this is just avionics. AUX hydraulic pumps are AC powered and I guess there are no inverters that will invert battery DC to AC?
And how is with DC busses manual talks about. Can you separare DC busses manualy via overhead panel?
I aslo don't know what is AC and what is DC powered.
PNEUMATIC SYSTEM
Provides pressure air for air cycle machine found in AC packs, start up engine, wings & engine anti ice, tank pressurization....
The question is if the bleed air from the engine for anti ice flows through wings leading edge and then return to the engine or is this one way path and bleed air blows through small holes in the leading edge?
Then another question is where is location of catalistic converter (to remove ozone). Then next question is how many heat exchangers are there. As manual says there are primary located before the compressor of air cyle machine and secondary after it. But manual also mentioned that there is air to air heat exchanger mounted in the engine bay so that airstream from the fan cooles the bleed air.
I am at the chapter about aircraft systems and since I am a bit more interested in engineering and since the PMGD manual are not very detailed and in some chapters the manual has huge gap or the explanation isn't really understandable I am asking those on this forum who are experts when come to aircraft technics.
HYDRAULIC SYSTEM
Manual says that B747 has 4 independant hydraulic systems. It has 4 engine driven demand pumps (one per engine), 4 hydraulic reservoars and 4 air driven pumps. Then it says that engine 4 has also AC electric driven AUX hydraulic pump - used only to power brakes durring ground towing usage. Then in the next statement it comes to a bit contradictious statement with previous one (each engine has air driven pump) as manual says that engine 1 and 4 have bleed air driven AUX hydraulic pump and engine 2 and 3 have AC electric driven AUX hydraulic pump.
Logicaly stated I'll say that there are 4 engine driven pumps, 4 AUX pumps (bleed air driven in engine 1,4 and AC driven in engine 2,3) + additionaly AC driven AUX pump for brakes.
Now I don't know if APU has aslo mechanicaly driven hydraulic pump, but I gues that it can run anyone of four engine AUX pumps via bleed air or AC electric (in case all four engines are malfunctioning).
ELECTRICAL SYSTEM
Manual says that each engine has 115V, 400Hz, 90kVA AC generator driven via constant speed drive, and all four generators can be paralled if they all works well (providing 400Hz). Then there are additional 2 AC generators driven by APU of the same characteristics as those on engines, but they aren't paralled. Then manual says there are also 2 nickel-cadmiun batterys onboard and if I understood they can only be charged via external power source. But on the next side manual says that there are 4 battery busses. Then manual says that there are automatic SSB that split left/right side of the plane (this is needed if sides are not powered via paralled generators).
What I don't know here how many batterys are on board and what they can power (manual says all standbay systems). I predicts that this is just avionics. AUX hydraulic pumps are AC powered and I guess there are no inverters that will invert battery DC to AC?
And how is with DC busses manual talks about. Can you separare DC busses manualy via overhead panel?
I aslo don't know what is AC and what is DC powered.
PNEUMATIC SYSTEM
Provides pressure air for air cycle machine found in AC packs, start up engine, wings & engine anti ice, tank pressurization....
The question is if the bleed air from the engine for anti ice flows through wings leading edge and then return to the engine or is this one way path and bleed air blows through small holes in the leading edge?
Then another question is where is location of catalistic converter (to remove ozone). Then next question is how many heat exchangers are there. As manual says there are primary located before the compressor of air cyle machine and secondary after it. But manual also mentioned that there is air to air heat exchanger mounted in the engine bay so that airstream from the fan cooles the bleed air.
Last edited by flybik; 15th Nov 2009 at 21:49.
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B747 hydraulics
I will just run through the hydraulics as lots to read here.
As you say each engine has a mechanical driven hyd pump - four systems.
Each system has an bleed air powered demand pump (ADP) in the rear of the pylon, also in each pylon is its own hydraulic system reservoir.
No.4 pylon also contains an AC powered aux pump (ACP) for primary brakes when on the ground.
As an extra some aircraft have an AC aux pump (ACP) in No.1 pylon for steering during towing.
Confusion:
On later aircraft some demand pumps changed from pneumatic to AC powered.
You will see the Nos 1 and 4 with bleed air and the nos 2 and 3 with AC powered demand pumps, but was dependant upon customer choice.
APU does not have a hyd pump fitted.
The APU will power the demand pumps with both air and AC electrics as required on the ground.
If an engine driven hyd pump fails or hyd pressure drops too low its demand pump will automatically cut in to supply oil flow and pressure. This pump will be powered by engine bleed air or AC electrics depending upon position.
If all 4 engines were malfuctioning that would be another story.
But I take it this was all 4 engine driven pumps then the demand pumps would auto cut in as required and then stop when the need had finished, the power would come from the engine bleed air or AC electric system.
Nos 1 and 4 are the most used hyd systems especailly during initial climb when gear retraction occurs and t/edge flaps are stowed and then similar for descent.
That's the basic layout but there will always be an airline that had some differences built in but the above is much the norm.
TW
As you say each engine has a mechanical driven hyd pump - four systems.
Each system has an bleed air powered demand pump (ADP) in the rear of the pylon, also in each pylon is its own hydraulic system reservoir.
No.4 pylon also contains an AC powered aux pump (ACP) for primary brakes when on the ground.
As an extra some aircraft have an AC aux pump (ACP) in No.1 pylon for steering during towing.
Confusion:
On later aircraft some demand pumps changed from pneumatic to AC powered.
You will see the Nos 1 and 4 with bleed air and the nos 2 and 3 with AC powered demand pumps, but was dependant upon customer choice.
APU does not have a hyd pump fitted.
The APU will power the demand pumps with both air and AC electrics as required on the ground.
If an engine driven hyd pump fails or hyd pressure drops too low its demand pump will automatically cut in to supply oil flow and pressure. This pump will be powered by engine bleed air or AC electrics depending upon position.
If all 4 engines were malfuctioning that would be another story.
But I take it this was all 4 engine driven pumps then the demand pumps would auto cut in as required and then stop when the need had finished, the power would come from the engine bleed air or AC electric system.
Nos 1 and 4 are the most used hyd systems especailly during initial climb when gear retraction occurs and t/edge flaps are stowed and then similar for descent.
That's the basic layout but there will always be an airline that had some differences built in but the above is much the norm.
TW
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PNEUMATICS
Bleed air for the LE is fed via a tube with little holes which blasts onto the rear side of the LE think of it as a o (tube) inside a D (the LE) the bottom of the D has periodical open sections to allow the bleed air to leak out.
Now the LE AI cannot be used with the LE flaps extended as the LE gets protected from the relative airflow by the LE flap ie Retracted _D extended D\ hope you can imagine what I'm talking about, this would result in overheating of the LE and therefore the restriction.
There is one pre cooler in each pylon to reduce the temp initally for the bleed system and it's components.
Each pack has a heat exchanger it's actually 2 (primary and secondary) stacked on top of each other and appear as one unit the cat converter is at part of the pack after the ACM is finished and prior to entering the A/C I think from memory it's after the water separator, but could have that wrong.
ELEC
Two batteries APU and MAIN, will have to get back to you on details. (APU batt does more than just the APU it's a bit understated naming it APU batt - a hangover from the classic where it was solely for the APU).
Bleed air for the LE is fed via a tube with little holes which blasts onto the rear side of the LE think of it as a o (tube) inside a D (the LE) the bottom of the D has periodical open sections to allow the bleed air to leak out.
Now the LE AI cannot be used with the LE flaps extended as the LE gets protected from the relative airflow by the LE flap ie Retracted _D extended D\ hope you can imagine what I'm talking about, this would result in overheating of the LE and therefore the restriction.
There is one pre cooler in each pylon to reduce the temp initally for the bleed system and it's components.
Each pack has a heat exchanger it's actually 2 (primary and secondary) stacked on top of each other and appear as one unit the cat converter is at part of the pack after the ACM is finished and prior to entering the A/C I think from memory it's after the water separator, but could have that wrong.
ELEC
Two batteries APU and MAIN, will have to get back to you on details. (APU batt does more than just the APU it's a bit understated naming it APU batt - a hangover from the classic where it was solely for the APU).
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Pneumatics, etc
Yes, lot's to answer here, but I'll throw in my 2pence worth:
Bleed air for leading edge heating is indeed blown into a cavity behind the leading edge devices. It vents overboard via rectangular cut-outs on the underside of the wing, just behind the leading edges. As a result of the design, wing anti-ice is ineffective with the leading edges extended (flaps 1 and greater).
Catalytic converter? Not sure about this one... Not in the engine pylon/cowling, that's for sure. However there may be one to process air for the cabin, downstream of the a/c packs. At cruising altitude, perhaps adding ozone to the atmosphere is a good thing?
Regarding heat exchangers, yes there is also an air-to-air exchanger in the bleed line from each engine, located in the cowling (or perhaps the pylon).
Batteries: yes, two onboard. One for the aircraft (located in flight deck), one for the APU (located in the APU compartment, forward of the turbine, and heated by a thermal blanket).
Yes, there are inverters to produce AC power from the batteries. They power quite a few items, best to check your manual, as exact details will differ by model/customer preferences.
No, you can't separate DC busses on the overhead panel. Well, not without pulling circuit breakers anyway!
Bleed air for leading edge heating is indeed blown into a cavity behind the leading edge devices. It vents overboard via rectangular cut-outs on the underside of the wing, just behind the leading edges. As a result of the design, wing anti-ice is ineffective with the leading edges extended (flaps 1 and greater).
Catalytic converter? Not sure about this one... Not in the engine pylon/cowling, that's for sure. However there may be one to process air for the cabin, downstream of the a/c packs. At cruising altitude, perhaps adding ozone to the atmosphere is a good thing?
Regarding heat exchangers, yes there is also an air-to-air exchanger in the bleed line from each engine, located in the cowling (or perhaps the pylon).
Batteries: yes, two onboard. One for the aircraft (located in flight deck), one for the APU (located in the APU compartment, forward of the turbine, and heated by a thermal blanket).
Yes, there are inverters to produce AC power from the batteries. They power quite a few items, best to check your manual, as exact details will differ by model/customer preferences.
No, you can't separate DC busses on the overhead panel. Well, not without pulling circuit breakers anyway!
The Classic and the 400s are slightly different.
Hyd.
The extra pumps on the Classic were termed ADPs and were air driven. They cut in automatically when the system pressure dropped below 2400psi (I think), or could be manually selected. There was also the DC Aux powered pump for pushback swithched on the FE's panel
The 400 extra pumps are known as Aux pumps. 1 and 4 are air driven and run when a servcie such as gear or flaps are selected. 2 and 3 are AC powered and are only really there to give pressure to the flying controls in emergency situations when main system pressure drops. They won't run otherwise.
No 4 pump in all 400s also had an Aux position which operates a separate DC pump to power the brakes. It's an option to fit it to the number 1 system as well. These tend to be found on GE powered aircraft where you can start two engines on one side at once on pushback. But if you do, you don't want to start the outside of the turn engines, otherwise the tug loses the battle!
The ADPs/Demand pumps are there to increase flow or back the the EDP in the event of it's failure. In the event of an engine failure and no ADP/Demand pump you lose the system as well as there is no way of cross feeding the systems. But if the HP core is still windmilling, the EPP will still produce workable pressure down to about 120 knots I gather.
Electrics:
The batteries on the Classic were on the flight deck (bloody silly place to put them - if one has a thermal runaway it fills the flight deck with noxious fumes. It happened on one of my company's aircaft and the guys had to land on Oxygen. How that got certifiied I don't know!). On the 400, the main batteries were in the radio electrics bay. They are normally charged by the TRUs from the IDGs, but they could be charged from a GPU or the APU on the gound. But if they were very flat they had to be removed as charging very flat NiCads with big currents can make them go bang.
Flight on batteries only is measured in minutes. Not a likely scenario or one you would want to be faced with. The batteries only power the hot batt busses, the batt busses and the AC standby busses.
You can start a 747 on batteries only. I did it once in a 400, but you have to watch the charge rates carefully afterwards. the APU battery takes a massive hit and you only really have one start attempt. All three batteries are the same and interchangebale. But you have to lug batteries the whole lenght of the aircraft to do that.
The SSB joined sync bus 1 and 2 to sync bus 3 and 4. The only time you would do this is if you had lost either sync bus to a double gen failure as you wouldn't connect one bad sync bus to another in case you lost the lot. But 90KVA is a massive supply, so one gen per sync bus was more than adequate.
The APU gens are the same as the ones on the IDGs and can be intercahnged. But as the APU gen frequency is controlled by the APU speed and there is no way of independantly adjusting them, they cannot be parralleled. The Classic ahd no safety interlinks and closing the SSB with both APU gens on line was not a good idea. The APU gens can't be used in flight or parrallled to the IDGs on the ground.
The elec system is very good on the 747 - it was almost a direct copy of the VC10's. The VC10 designers all got jobs at Seattle when Vickers made them redundant.
Pneaumatics.
The de-ice blows air around the inside leading edges and is a total loss system. It doesn't work itf the LE devices are deployed. It's very hot and an anti-ice overheat is a biggy as far as emergencies go as it can start melting metal!
The cat is an option on 400s only (I think). It's between the packs and the plenum chamber. You have no control over it from the flight deck.
All of the info on this thread is general as Boeing build aircraft the way the customer wants. so there are a lot of user specific options. there are also a lot of differences between aircraft in the same fleets in some airlines.
And I haven't flown one for over 4 years, so my memory is getting dim!
Hyd.
The extra pumps on the Classic were termed ADPs and were air driven. They cut in automatically when the system pressure dropped below 2400psi (I think), or could be manually selected. There was also the DC Aux powered pump for pushback swithched on the FE's panel
The 400 extra pumps are known as Aux pumps. 1 and 4 are air driven and run when a servcie such as gear or flaps are selected. 2 and 3 are AC powered and are only really there to give pressure to the flying controls in emergency situations when main system pressure drops. They won't run otherwise.
No 4 pump in all 400s also had an Aux position which operates a separate DC pump to power the brakes. It's an option to fit it to the number 1 system as well. These tend to be found on GE powered aircraft where you can start two engines on one side at once on pushback. But if you do, you don't want to start the outside of the turn engines, otherwise the tug loses the battle!
The ADPs/Demand pumps are there to increase flow or back the the EDP in the event of it's failure. In the event of an engine failure and no ADP/Demand pump you lose the system as well as there is no way of cross feeding the systems. But if the HP core is still windmilling, the EPP will still produce workable pressure down to about 120 knots I gather.
Electrics:
The batteries on the Classic were on the flight deck (bloody silly place to put them - if one has a thermal runaway it fills the flight deck with noxious fumes. It happened on one of my company's aircaft and the guys had to land on Oxygen. How that got certifiied I don't know!). On the 400, the main batteries were in the radio electrics bay. They are normally charged by the TRUs from the IDGs, but they could be charged from a GPU or the APU on the gound. But if they were very flat they had to be removed as charging very flat NiCads with big currents can make them go bang.
Flight on batteries only is measured in minutes. Not a likely scenario or one you would want to be faced with. The batteries only power the hot batt busses, the batt busses and the AC standby busses.
You can start a 747 on batteries only. I did it once in a 400, but you have to watch the charge rates carefully afterwards. the APU battery takes a massive hit and you only really have one start attempt. All three batteries are the same and interchangebale. But you have to lug batteries the whole lenght of the aircraft to do that.
The SSB joined sync bus 1 and 2 to sync bus 3 and 4. The only time you would do this is if you had lost either sync bus to a double gen failure as you wouldn't connect one bad sync bus to another in case you lost the lot. But 90KVA is a massive supply, so one gen per sync bus was more than adequate.
The APU gens are the same as the ones on the IDGs and can be intercahnged. But as the APU gen frequency is controlled by the APU speed and there is no way of independantly adjusting them, they cannot be parralleled. The Classic ahd no safety interlinks and closing the SSB with both APU gens on line was not a good idea. The APU gens can't be used in flight or parrallled to the IDGs on the ground.
The elec system is very good on the 747 - it was almost a direct copy of the VC10's. The VC10 designers all got jobs at Seattle when Vickers made them redundant.
Pneaumatics.
The de-ice blows air around the inside leading edges and is a total loss system. It doesn't work itf the LE devices are deployed. It's very hot and an anti-ice overheat is a biggy as far as emergencies go as it can start melting metal!
The cat is an option on 400s only (I think). It's between the packs and the plenum chamber. You have no control over it from the flight deck.
All of the info on this thread is general as Boeing build aircraft the way the customer wants. so there are a lot of user specific options. there are also a lot of differences between aircraft in the same fleets in some airlines.
And I haven't flown one for over 4 years, so my memory is getting dim!
Last edited by Dan Winterland; 16th Nov 2009 at 01:51.
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No, you can't separate DC busses on the overhead panel. Well, not without pulling circuit breakers anyway!
MD
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Bleed air for leading edge heating is indeed blown into a cavity behind the leading edge devices.
Then in the next statement it comes to a bit contradictious statement with previous one (each engine has air driven pump) as manual says that engine 1 and 4 have bleed air driven AUX hydraulic pump and engine 2 and 3 have AC electric driven AUX hydraulic pump.
A minor point to be sure, but I believe you can isolate the DC busses on the overhead panel: by pressing the Bus Tie Breaker switch, you also open the respective DC Isolation Relay...
You can start a 747 on batteries only. I did it once in a 400, but you have to watch the charge rates carefully afterwards. the APU battery takes a massive hit and you only really have one start attempt. All three batteries are the same and interchangebale. But you have to lug batteries the whole lenght of the aircraft to do that.
I'm not sure what you mean by starting a 747-400 on batteries. Bleed air is required, so you need more than batteries. Also, batteries will not open the AC-powered Wing Bleed Isolation Valves if they have been previously closed, so you cannot get External Air into the wing bleed ducts for engine start. Just curious, but why would there be a large drain on the batteries? Other than the ignitors and EEC power(for less than a minute) for a single engine and the usual Standby Power stuff, I don't see any additional requirements. A single 747-400 battery can pump 50 amps for an hour on the test bench.
[quote]The APU gens can't be used in flight or paralleled to the IDGs on the ground.[quote]
Later/modified Elec Bus Control Units allow APU power if all engines generators are out (however, the APU cannot be started inflight ... at least not without a lot of CB pulling).
Rgds.
NSEU
Don't know much about the 747 but.
Why would a customer want to have the operation of wing anti-ice with the LED'S deployed as an 'option' ?
I would think all customers would want this feature or am I missing something?
Why would a customer want to have the operation of wing anti-ice with the LED'S deployed as an 'option' ?
I would think all customers would want this feature or am I missing something?
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Why would a customer want to have the operation of wing anti-ice with the LED'S deployed as an 'option' ?
I just looked at the wiring schematics for a number of different airlines, but couldn't find any with the inhibit fitted, but having said that, all of these airlines have manual operation of WAI (apart from the automatic shutoff on the ground). If a disable relay is fitted for an on-ground inhibit, then I'm sure it wouldn't be too difficult to string a few wires from the Flap Control Units to the WAI relays.I suspect the effect of air shielding was later considered to be not as serious as first thought, so Boeing didn't mandate the fitment of this automation.
Cheers.
NSEU
There are very few places or times in the world where you will gather enough ice after extension of the LEDs to matter enough to justify the cost of fitting an option like that, I would think.
Holding without ATC allowing sufficient speed to keep the aircraft clean would be the only problem, I would think.
Holding without ATC allowing sufficient speed to keep the aircraft clean would be the only problem, I would think.
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Checkboard, the option is not to add heating to LE devices, but to inhibit the heating of the leading edge of the wing when the leading edge flaps are extended.
When deployed, the LEDs move up and in front of the wing leading edge. Some of them have a small air gap for air to flow between them and the wing, but others don't(if I remember correctly there is a rubber seal on the back of them which actually contacts the wing, allowing no air flow. Without cooling airflow, the LE's might get a bit hot. I've seen what happens when the heat is not inhibited on the ground, the metal wing leading edges buckle.
Rgds
NSEU
When deployed, the LEDs move up and in front of the wing leading edge. Some of them have a small air gap for air to flow between them and the wing, but others don't(if I remember correctly there is a rubber seal on the back of them which actually contacts the wing, allowing no air flow. Without cooling airflow, the LE's might get a bit hot. I've seen what happens when the heat is not inhibited on the ground, the metal wing leading edges buckle.
Rgds
NSEU
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APU Generators
The APU gens are the same as the ones on the IDGs and can be intercahnged.
APU generators are not interchangeable with IDGs, the IDG is a combined GEN/CSD. It was possible to interchange early 747 APU gens with PW and GE engine gens but not RR.
TW
''3 batteries? An option?
I'm not sure what you mean by starting a 747-400 on batteries.''
2 main batteries in the radio electric bay and 1 in the apu bay. All 3 are the same item and can be interchanged.
With just DC from the main batts running the aircraft, you start the APU from the APU bat. When that is running, you have AC and bleed air to start the main engines. Í only did that once when picking up an aircraft from maintenance on a remote stand and the power cart's frequency was too far out to connect it to the aircraft. The literature stated that the APU batt was good for three starts, but seeing how long it took for the charge rate to come down afterwards, I don't believe it. I would be suprised if we could have got another start out of it.
''APU generators are not interchangeable with IDGs, the IDG is a combined GEN/CSD'''
I thought I remebered reading the gen part of the IDG could be unbolted and fitted in place of the APU gen and vice versa. This was on early GE powered 400s, but I could be getting confused with the Classic.
Of course, all of these could be options. There seem to be a lot in Boeings unlike in Airbus where they believe you should accept the way they build it.
I'm not sure what you mean by starting a 747-400 on batteries.''
2 main batteries in the radio electric bay and 1 in the apu bay. All 3 are the same item and can be interchanged.
With just DC from the main batts running the aircraft, you start the APU from the APU bat. When that is running, you have AC and bleed air to start the main engines. Í only did that once when picking up an aircraft from maintenance on a remote stand and the power cart's frequency was too far out to connect it to the aircraft. The literature stated that the APU batt was good for three starts, but seeing how long it took for the charge rate to come down afterwards, I don't believe it. I would be suprised if we could have got another start out of it.
''APU generators are not interchangeable with IDGs, the IDG is a combined GEN/CSD'''
I thought I remebered reading the gen part of the IDG could be unbolted and fitted in place of the APU gen and vice versa. This was on early GE powered 400s, but I could be getting confused with the Classic.
Of course, all of these could be options. There seem to be a lot in Boeings unlike in Airbus where they believe you should accept the way they build it.
Previous posts have covered your questions to a large extent but with some confusing data.
There are a number of differences between 747 Classic aircraft and the 747-400.
Hydraulics
All 747’s have 4 independent systems. Each system is powered by an Engine Driven Pump (EDP) as the primary power source and a “Demand Pump” as a supplemental source.
On a classic 747’s all demand pumps were Air Driven Pumps (ADP’s). On a standard 747-400 only systems #1 & #4 had the same ADP’s and #2 & #3 had ACMP’s (AC Motor Pumps) since they did not need the high flow rate of an ADP. However, some operators requested Boeing to install ADP’s in all 4 systems. On a standard 747 there is a low output AC pump in #4 system for ground towing. Some operators requested an identical pump in #1 system.
In flight the “Demand Pump” in system #2 & #3 never operated unless there was a failure of the EDP or the engine was shut down .
The ADP in systems #1 & #4 always operated during gear and TE Flap operation as the EDP could not meet the flow demand on its own.
There are no APU driven hydraulic pumps. Use a Demand Pump (whether ADP or ACMP) for hydraulic power using bleed air or electric power from the APU.
A 747 APU cannot be used in flight for electric power.
Electrical
There are 2 batteries, Main & APU. They are charged whenever the aircraft is powered regardless of source.
There is a Standby Power system which powers the very essential loads which is probably confusing as this is more important than the Essential Power system ie. the Standby Power system powers less equipment than the Essential Bus system. Yes, it is all avionics and last ditch avionics at that. There is an inverter that powers very essential avionics loads only. If all engines fail a 747’s windmilling engines’ provide enough hydraulic power to maintain control without recourse to a RAT or use of electric pumps provided speed is maintained above a certain figure.
Pneumatics
Wing Anti-Ice air exits to ambient via slots in the lower surface.
Contrary to some previous posts Wing Anti-Ice is inhibited on the ground. It is only available in flight regardless of LE device operation. The only inhibit is air/ground logic.
Catalytic converters fit between the Pack Valve and primary heat exchanger but are an optional feature. There is 1 heat exchanger per pack. The heat exchanger physically is a single unit but has two separate flow paths: primary and secondary The air flows from the Pack Valve to the primary section then to the ACM and back to the secondary section.
The heat exchanger in the nacelle is a Precooler, which reduces the bleed air temperature to the temperature required by the pneumatic and air conditioning systems. It may be installed in the pylon or on the engine depending in engine type.
There are a number of differences between 747 Classic aircraft and the 747-400.
Hydraulics
All 747’s have 4 independent systems. Each system is powered by an Engine Driven Pump (EDP) as the primary power source and a “Demand Pump” as a supplemental source.
On a classic 747’s all demand pumps were Air Driven Pumps (ADP’s). On a standard 747-400 only systems #1 & #4 had the same ADP’s and #2 & #3 had ACMP’s (AC Motor Pumps) since they did not need the high flow rate of an ADP. However, some operators requested Boeing to install ADP’s in all 4 systems. On a standard 747 there is a low output AC pump in #4 system for ground towing. Some operators requested an identical pump in #1 system.
In flight the “Demand Pump” in system #2 & #3 never operated unless there was a failure of the EDP or the engine was shut down .
The ADP in systems #1 & #4 always operated during gear and TE Flap operation as the EDP could not meet the flow demand on its own.
There are no APU driven hydraulic pumps. Use a Demand Pump (whether ADP or ACMP) for hydraulic power using bleed air or electric power from the APU.
A 747 APU cannot be used in flight for electric power.
Electrical
There are 2 batteries, Main & APU. They are charged whenever the aircraft is powered regardless of source.
There is a Standby Power system which powers the very essential loads which is probably confusing as this is more important than the Essential Power system ie. the Standby Power system powers less equipment than the Essential Bus system. Yes, it is all avionics and last ditch avionics at that. There is an inverter that powers very essential avionics loads only. If all engines fail a 747’s windmilling engines’ provide enough hydraulic power to maintain control without recourse to a RAT or use of electric pumps provided speed is maintained above a certain figure.
Pneumatics
Wing Anti-Ice air exits to ambient via slots in the lower surface.
Contrary to some previous posts Wing Anti-Ice is inhibited on the ground. It is only available in flight regardless of LE device operation. The only inhibit is air/ground logic.
Catalytic converters fit between the Pack Valve and primary heat exchanger but are an optional feature. There is 1 heat exchanger per pack. The heat exchanger physically is a single unit but has two separate flow paths: primary and secondary The air flows from the Pack Valve to the primary section then to the ACM and back to the secondary section.
The heat exchanger in the nacelle is a Precooler, which reduces the bleed air temperature to the temperature required by the pneumatic and air conditioning systems. It may be installed in the pylon or on the engine depending in engine type.
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Contrary to some previous posts Wing Anti-Ice is inhibited on the ground. It is only available in flight regardless of LE device operation. The only inhibit is air/ground logic.
Yes, WAI is inhibited on the ground. There is nothing contrary here. My reference to damaged leading edges were a result of a system failure.
A 747 APU cannot be used in flight for electric power.
The ADP in systems #1 & #4 always operated during gear and TE Flap operation as the EDP could not meet the flow demand on its own.
2 main batteries in the radio electric bay and 1 in the apu bay. All 3 are the same item and can be interchanged.
Rgds.
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CV880, KLM (Royal Dutch Airlines) have the leading edge inhibit for WAI (I've just found a wiring schematic for it). I'm sure there are other airlines with this option. LH?
For those with access to Boeing manuals ...
Boeing Wiring Diagram Manual (WDM 27-51-11) shows an output from the Flap Control Units (pin H6 in plugs DM7879CA, DM7881CA & DM7880CA), in dashed lines, to "30-11-11" (which refers to the WAI). However, when you go to 30-11-11, there is no cross reference to the flaps. "H6" is internally labelled "FLP 1 NOT RET" (???)
Rgds.
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Another B744 electrical question
Normally batteries (APU and Main) are recharged continuously by AC Bus 1 through the Ground Service Bus and the battery chargers. Meanwhile DC Bus 3 powers the Main Battery Bus and the APU Battery Bus.
If one should lose AC Bus 1 in flight, will the batteries slowly discharge? Or will DC Bus 3 keep them charged?
MD
If one should lose AC Bus 1 in flight, will the batteries slowly discharge? Or will DC Bus 3 keep them charged?
MD
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The batteries will discharge relatively slowly. Normally the Batteries are not connected to the Main and APU Battery Busses, unless you do something silly like put the Standby Power switch to BAT. However, the batteries will be connected to the Main HOT and APU HOT Battery Busses.
There are quite a few things on the hot battery busses, but some will be low current, like the clocks, and some things will be running quite nicely on their normal AC power.
The loss of AC 1 will probably keep you rather busy, so don't forget about the Batteries
Rgds.
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There are quite a few things on the hot battery busses, but some will be low current, like the clocks, and some things will be running quite nicely on their normal AC power.
The loss of AC 1 will probably keep you rather busy, so don't forget about the Batteries
Rgds.
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Thanks for the prompt response.
I thought the Batteries were connected to their respective Battery Busses (through their Hot Battery Busses) every time the Battery Switch was selected on? I just wasn't sure whether power could flow back to the batteries from the Battery Busses...
Now I'm curious, as our FCOM has very little information on this... aside from A/Throttle, EPR limit indications, LNAV/VNAV, Antiskid and left side pitot heat what else happens? 
Normally the Batteries are not connected to the Main and APU Battery Busses
The loss of AC 1 will probably keep you rather busy, so don't forget about the Batteries
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The Hot Bat buses will only be connected to their respective Battery Buses until DC 3 is powered. Doing this energises the Battery Transfer Relay and de-energises the Battery Relay. With the Battery Relay de-energised, the Hot & regular bat buses are divided.
Well, I thought the items you mentioned would keep you busy : ). I have a long list of items affected by AC 1, but not handy at the moment. Of course, there are variations between different versions of the -400, including engine type differences.
From memory, I recall the C IRU will be running off one of the Hot Bat Buses, but won't cut out after 5 minutes like it does when you're running on Standby Power only.
Cheers
NSEU.
Well, I thought the items you mentioned would keep you busy : ). I have a long list of items affected by AC 1, but not handy at the moment. Of course, there are variations between different versions of the -400, including engine type differences.
From memory, I recall the C IRU will be running off one of the Hot Bat Buses, but won't cut out after 5 minutes like it does when you're running on Standby Power only.
Cheers
NSEU.