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Question About External Air/Power on the Queen

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So I have been reading up on the Queen the last few weeks in anticipation for release.  The manual that I have makes no mention of using external air in the normal operating procedures.  The only mention of external power, is that it may be already in use when entering the aircraft.  What strikes me as odd, is that the manual recommends turning the APU on right away during the initial cockpit preparation.  I have always been taught to use external air/power when available to save fuel and then start the APU about 5-10 minutes before push/start.  Now, I'm not going to mention the name of this carrier for privacy reasons, but I know that RSR would probably know the reasoning behind this as he has probably used this same manual ;).  I realize that this manual has a revision date of 1997, but I also have the manuals for every other aircraft at this airline during the 90s, and all of them state that external air/power should be used when available.  Why wouldn't the B747-400 manual recommend that either?  Here are the manual pages in question front and back (Note the text section at the top on the first image):

 

7472.jpg

 

Next Page:

7471.jpg

 

Then next up in the Cockpit Preparation - Captain section, the manual has the procedures to set up the Air Conditioning w/ the running APU as well, again with no mention of external air.

 

7474.jpg

 

Regards,

Rob

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You will get flight manuals I guess with the new 747 (we got them with the NGX and 777). When you do, you will need to use the supplementary procedure for what you want to do at the most suitable time.

 

Do your really old procedures have a supplementary procedure section? Check that

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You will get flight manuals I guess with the new 747 (we got them with the NGX and 777). When you do, you will need to use the supplementary procedure for what you want to do at the most suitable time.

 

Do your really old procedures have a supplementary procedure section? Check that

 

It has an additional section, but the only relevant section in it that mentions external power, is a procedure for Operation w/ Single External Power Source.  Like I said, I have other manuals from the same airline during the same time period, such as the 727, 757, 767, 737-300/500, A320, DC-10, even the 747 classic, and they all say to use external air/power when available.  That's why I find it strange that the B744 manual wouldn't mention it.  I'm just trying to figure out why. 

 

Regards,

Rob

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Hi rob

 

They must have had another volume or a different manual that gave them a step by step for supplementary tasks

 

Good luck

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my guess would be entirely on where in the world you are parked,and what facilities are available.Also the prevailing time and noise conditions that are applicable at that airport.

So while the procedures list the order they may not be available or applicable.

If it's first flight of day the engineers will probably been on and powered it all up anyway (we're nice like that !!)

Cheers

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Also, here's a video I found which seems to show the same thing on another major airline that operates the B744.  External power is connected and says available, however, the APU is on and appears to be the primary source of electrical power throughout all of the preflight.  It's not until 11:15 in the video that they request Ground Power be disconnected.

 

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If you purchased the airline2sim b777 cadet training captain mycroft gives a detailed explanation on power and which source it uses.

 

Greetings,

 

Koen meier

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If you purchased the airline2sim b777 cadet training captain mycroft gives a detailed explanation on power and which source it uses.

 

Greetings,

 

Koen meier

 

Thats the T7 not the Queen

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Thats the T7 not the Queen

The reason to start up the app is to now if it isn't failed because a company sop and their Mel say that the can either operate without an apu or not. External air is used to cooldown the cabin if the out side temperature is too high.

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The reason to start up the app is to now if it isn't failed because a company sop and their Mel say that the can either operate without an apu or not. External air is used to cooldown the cabin if the out side temperature is too high.

 

A few questions, even if checking if APU is operational, why use it throughout the entire pre-flight?  Surely, on a plane the size of the B744 that wastes a ton of fuel.  Next, if the APU is already on and running, why use external air?  Usually, on most other aircraft, external air is used in normal ops and then APU is used if external air is not adequate for cooling.  Like the manual says, the aircraft will probably be powered by external power, and while not mentioned, I'd assume also external air would be hooked up by engineering or left on by previous crew.  So I'm trying to figure out, why the seemingly standard procedure is to start the APU so early in the pre-flight procedure.  Are there any system quirks that would require this?  I can't see any advantages to doing it so early.  Seems like it just is a waste of money if you have external air/power available, yet a bunch of operators seem to operate it extremely early on the B744 compared to other fleet types.  I like this though - Very good discussion!  Hopefully, RSR will chime in!

 

-Rob

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Simply put -- delaying APU start is what the Airbus manuals refer to as a "Green Operating Procedure" -- in other words, it is a procedure to save fuel/reduce noise etc that diverges from the standard way of operating but is approved as it does not impact on safety (indeed, the A320 supplementary procedure simply says "APU start.........DELAY" and isn't any more specific about it than that). The B747 FCOM I have simply says in the normal procedures (P2 Preflight Procedure) -- "APU Selector (if needed)....START, then ON" -- so it doesn't necessarily require the APU to be started at that stage, but if you don't have ground power then it would be necessary to start the APU at that point in order to establish electrical power for the rest of the procedures.

 

Some airports have noise restrictions on the running of APUs, but these are normally much less restrictive for widebodies because of the additional power (of both the electrical and cooling variety) they require, and if it the ambient temperature is particularly cold (or extremely hot) the restrictions are often relaxed further -- for example, here's the Heathrow restrictions:

 

FPGWXoW.jpg

 

Low-pressure pre-conditioned air can often be a bit wheezy (if it is available at all) and the APU is much more efficient at heating/cooling the cabin (note that the LP conditioned air does not go through the packs -- is a different thing to the HP external air that can be used to start the engines in the event of an unserviceable APU: as I understand it, external HP air would not normally be used to drive the packs).

 

There are other advantages to starting the APU early as well: the most notable of which would be to ensure it actually does start! (It would be a bit embarrassing to get everything ready to push in time for your slot and then discover the APU is unserviceable and have to call for a start cart). This is as one might imagine less of an issue for short-haul aircraft where you can start it early on the first flight of the day and subsequently be reasonably confident it will in fact start for the next sector (and indeed if it failed in between you would likely know about it when you tried to start it on the taxi-in).

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Low-pressure pre-conditioned air can often be a bit wheezy (if it is available at all) and the APU is much more efficient at heating/cooling the cabin

 

This is a real consideration when it's hot or cold, the LP air does not provide any regulation of temperature and soon the flight deck becomes quite stuffy. 

 

 

 


external HP air would not normally be used to drive the packs).

 

Very true, the source of external HP air is generally much louder than the on-board APU.

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LP air is pretty weak, and as Dan mentioned, it isn't regulated very well. When I worked ramp at IAD, it was all we could do for the SAABs (they didn't have APUs), but they would either be awfully hot or frigid cold, depending on the outside air.

 

HP air is pretty rare. It's mainly used for engine starts where the APU is inop.

 

With that in mind, it's best to get the APU running to get better air on the plane. If you're using the APU, then you might as well switch power over to it. Rampies have been known yank ground power without confirmation from the crew (at some locations more than others). The earlier you get away from the GPU, the better chance you have at avoiding that mess.

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This is all very interesting. As I was reading more into the Pneumatic/Air Conditioning system, it would appear that in my manual, this particular airline's 747s only had high pressure external air receptacles aft of the Packs that would have to go through the packs in order to provide air conditioning. It makes no mention in both the textual description or the system diagram of low pressure external air connecting directly into the mix manifold. This would explain why they start the APU at the beginning of preflight. Otherwise, the crew would have no airflow unless using high-pressure external air. So did not all 747s have a low pressure receptacle? Or was this something added to most of them later on?

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Rampies have been known yank ground power without confirmation from the crew
I have done that to myself a few times. Its usually a Picard facepalm moment, if ever there was one...

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LP air is pretty weak, and as Dan mentioned, it isn't regulated very well. When I worked ramp at IAD, it was all we could do for the SAABs (they didn't have APUs), but they would either be awfully hot or frigid cold, depending on the outside air.

 

HP air is pretty rare. It's mainly used for engine starts where the APU is inop.

 

With that in mind, it's best to get the APU running to get better air on the plane. If you're using the APU, then you might as well switch power over to it. Rampies have been known yank ground power without confirmation from the crew (at some locations more than others). The earlier you get away from the GPU, the better chance you have at avoiding that mess.

 

Our guy from a well know sandy airline related a tale of one their 777s readying for departure at a regional UK airport. The APU hadn't yet been started and the Skipper in a moment of brain fartedness just reached up and selected Primary (they didn't have secondary connected) to avail. Clunk, darkness. Apparently the SOP here is to not panic and select it back on instantly as that upsets all the CBs but quick as a flash he punched back to on. Clunk, myriad of yellow cautions that took an hour to clear. Happiness in a T7 is P-A-D-P-A. T7 Cadets will get that one :)  

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As I was reading more into the Pneumatic/Air Conditioning system, it would appear that in my manual, this particular airline's 747s only had high pressure external air receptacles aft of the Packs that would have to go through the packs in order to provide air conditioning. It makes no mention in both the textual description or the system diagram of low pressure external air connecting directly into the mix manifold.

 

 

Seems unlikely, but perhaps there is an option to have no conditioned air connectors. I'm only aware of an option to have two (on a Freighter) instead of the usual three. Experts?

 

Airlines do come up with many odd rules for APU usage. Whilst I agree that turning on the APU early avoids a lot of hassle in the final fraught stages of departure, the beancounters (company accountants) think they know better.

 

Hopefully they've factored these into the equation:

Sometimes external conditioned air is insufficient and pilots can stop passengers boarding if the aircraft isn't cool enough. Delays incur costs and make pax unhappy (and may switch to another airline)

Sometimes power transfers between ground and APU can cause electrical glitches which may need time to be sorted (delays and angry pax). Pax may stress out when the emergency exit lights come on.

Sometimes engineer or groundstaff time could be better spent fixing last minute defects than stowing electrical and conditioned air stuff (more delays and angry pax) Rushing can cause engineers to make maintenance errors or injure themselves. Costs variable (zero dollars to hundreds of millions).

If the APU doesn't start (delays and angry passengers).

 

The beancounters usually always win. :fool:

 

For the technically minded... There is a check valve on each conditioned air connector. You shouldn't have conditioned air on at the same time as the packs as the pressures from each source may vary and cause the check valve to oscillate... leading to premature check valve failure (or you may damage the conditioned air system. Sometimes these check valves can break away from their hinges. If the check valve breaks off completely (and disappears into the duct), the associated pack then discharges its air into the (honeycomb composite) wing to body fairings. At some point the pressurized wing to body fairings may decide to part company with the aircraft. They go off with a boom. =@  Since my old airline's fuel saving policy came into effect, I had never seen so many problems with this system.

 

Rant off.... :wink:

 

Cheers

John H Watson

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Seems unlikely, but perhaps there is an option to have no conditioned air connectors. I'm only aware of an option to have two (on a Freighter) instead of the usual three. Experts?

 

Excellent post sir. So normally, the 744 has three external air connectors? I'm assuming 1 for low pressure pre-conditioned air and 2 for high pressure bleed air? I've found another manual, this one straight from Boeing instead of United's own training center. This one also only mentions high pressure bleed air on pg. 302 of the attached pdf and nothing about low pressure pre-conditioned air.

 

https://www.google.com/url?sa=t&source=web&rct=j&url=http://landrover.narod.ru/gershon/AIRPLANTANK/747-400_operations_manual.pdf&ved=0ahUKEwjs-vyEyMDRAhWDKyYKHUIHAhcQFggjMAQ&usg=AFQjCNFKpHVAA7BwrnsqWohx15ez4fNSPA&sig2=BO0Y9akj_8y4TIVmA6MFhg

 

This whole time, I've assumed the two air receptacles behind the packs were the only ones and that low and high pressure both connect to them. I've been driving myself nuts looking at the diagram trying to figure out how low pressure pre-conditioned air could go from these two receptacles to the mixing manifold with the packs off(which would close the pack control valve and restrict further flow to the mixing manifold unless it somehow went through the trim air manifold.) But knowing now, that there is a third receptacle for pre-conditioned air that is ahead of the packs and connects directly to the mixing manifold makes a lot more sense. So that must've been an option on earlier passenger 744s. I've seen some United 744s hooked up to external air, so maybe some of their earlier birds, elected for the 2 receptacle option, which would explain why my manual doesn't mention pre-conditioned air. Now that I think about it, didn't the first version of the PMDG 747 only offer pneumatic high pressure air?

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So normally, the 744 has three external air connectors?

 

 

My old airline had six.:

 

Three were for hp air (hot, high pressure bleed air). These all feed into the centre bleed manifold. I've seen KLM manuals with only 2 however.  I thought it might be an engine thing (some engines being harder to start than others), but I think all our aircraft had 3 (and we had RB211's and CF6's).

 

Three for cool/cold lower pressure conditioned air which were fed into the aircon manifold downstream of the individual packs. Freighters optionally have two (maybe less, but I don't know why they would). I wouldn't call it super low pressure. You would want to turn off the conditioned air supply before you disconnected the hoses.

 

Here's a pic of the high pressure connectors (bleed air supplied by a "start cart").... all go into the one spot behind some small panels.

ExtAir3.jpg

 

The conditioned air connection points are in the same general area (forward of these) and are behind large hinged pack access panels (sorry, no pics)

 

Cheers

John H Watson

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My old airline had six.:

 

Three were for hp air (hot, high pressure bleed air). These all feed into the centre bleed manifold. I've seen KLM manuals with only 2 however.  I thought it might be an engine thing (some engines being harder to start than others), but I think all our aircraft had 3 (and we had RB211's and CF6's).

 

Three for cool/cold lower pressure conditioned air which were fed into the aircon manifold downstream of the individual packs. Freighters optionally have two (maybe less, but I don't know why they would). I wouldn't call it super low pressure. You would want to turn off the conditioned air supply before you disconnected the hoses.

 

Here's a pic of the high pressure connectors (bleed air supplied by a "start cart").... all go into the one spot behind some small panels.

ExtAir3.jpg

 

The conditioned air connection points are in the same general area (forward of these) and are behind large hinged pack access panels (sorry, no pics)

 

Cheers

John H Watson

 

Thanks, this helps a lot.  I know UAL has PW4056s on their 747s.  Maybe the connections are a little different as you had mentioned.  This leads to my eventual question - What configuration will the PMDG 747v3 have, or does this change with airline specific options liveries?

 

Regards,

Rob

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I don't think it's going to make much difference to what you would experience in the sim unless PMDG models air mass in the bleed ducts :Tounge: e.g. pressure is not always a good indication of what a system will do (e.g. the AUX hydraulic pumps output around 3000psi... but they are small pumps and would have problems doing the same job as Air-Driven Pumps such as retracting gear). I recall that the AUX pumps even move the flaps more slowly than the ADPs during ground tests. 

 

Assuming a perfect airport, the aircraft should be supplied with constant pressure at all 4~6 connectors. The hp external air all goes into the same part of the centre bleed duct. You can't change where it goes... Same for the cool conditioned air... it goes into the mix manifold.

 

I have a photo of an ECS synoptic showing EXT AIR providing pneumatic pressure to the packs and the  L duct pressure shows only 11psi and the R duct pressure shows 12psi. This is not enough to start an engine, but we could go into a "start mode" on the ground cart...  and hopefully this would provide enough pressure for engine start.

 

The logic behind the message EXT AIR on the synoptic is very complex. There are no microswitches to tell the airplane that the external air hoses are plugged in. The airplane has to see the effect of ext air before it will display EXT AIR.

 

Hope this makes sense.

Cheers

John H Watson

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