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Guest pilotbrian0

Curiosity about Pack Management on 744(F)

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Guest pilotbrian0

This question applies to both teh 744 and 744F.It may seem like I'm splitting hairs here since I am using the packs on normal mode, they are working, they are splitting the work between the 3 of them etc etc.The question is: What is the trigger for the packs to switch from A to B or back to A at the end of a flight? The manual states that it automatically switches from one flight to the next, but I can't find anything definitive about what the trigger is. I wouldn't even ask, except that there are times when I don't completely power down the plane at the destination For example: There was one route I was flying where the turnaround was a mere 25 mminutes. Now, assuming passenger boarding and whatnot, that means... no time to power off the cockpit (OK OK so if the flight attendants flipped that one switch at the back and there was a GPU connected I could completely power down, for our sake, let's assume no GPU, so I HAVE to have the APU running).So, what is the trigger? Is it all packs turned off at landing? Is it "On the ground" then packs off? Would really appreciate an answer so I can be sure that I trigger the auto switch when I do such short turnarounds.-Brian

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I don't suppose most pilots really care if it's A or B. I guess it's more of an issue with making sure that they get equal usage.Good question though. I don't imagine you'd have to power down completely. I'd guess the trigger would be either some time after touchdown, or when all engines have been switched off.PS. Is your flight with a 25 min turnaround a real world flight? I ask becasue I'm wondering about the brake cooling period (ie you may be weight limited in that situation)Hope I've helpedPaul

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Guest pilotbrian0

funny you should mention that.The flight is a real world flight... kinda...It's actually a situation where I landed like 4 hours early and said, "OK, now, who's the next 747 to leave here?" and there was one 25 minutes later.I got lucky and had a light brake landing (long runway REALLY light coming in) and was able to get away without weight limitations.Having just completed a flight, I noticed that it switched to A as soon as all 4 engines had shut down (B had been running all the way to Chicago from Hong Kong, real time, autopilot off for more than half the trip, now let me tell you, THAT is entertainment! :D)-Brian

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Guest pilotbrian0

I fly without AP all the time.Infact, I don't think I've more than twice turned the autopilot on before hitting Cruise flight.I also have an aircraft with a modified panel to remove the autopilot. It's my "Let's just FLY" aircraft (a modified default C-172)-Brian

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"The question is: What is the trigger for the packs to switch from A to B or back to A at the end of a flight? The manual states that it automatically switches from one flight to the next, but I can't find anything definitive about what the trigger is. I wouldn't even ask, except that there are times when I don't completely power down the plane at the destination"There's nothing in my manuals about the source of the trigger, but it may be an air to ground transition.Note that there won't be a normal automatic switchover if electrical power is interrupted. Since switchover is also controlled by failures (including loss of elec power to the Pack Temperature Controller) the first controller to power up will have command. However, during normal aircraft power up (from a dead ship), certain busses come online first, so, almost invariably, with the Pack controllers in NORM, PTC "A" will be the controller in command.Cheers.Q>

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Guest pilotbrian0

Sorry, but the manual clearly states(11-8):The Pack controller logic will automatically change the pack control mode between each subsequent flight.And for that matter, how are you starting the aircraft that some buses come online and some don't? The aircraft is designed so that all 4 buses come on together unless circumstances prevent that.Also, I've found that the trigger is on landing, as the controllers switch over from A to B or back to A between when I'm on final and when I'm taxiing in. I have had ONCE a situation in which the previous flight had been A. I power up, and during that process, for some reason a couple of buses weren't powered (don't remember which ones) and it goes to A originally. Once all the buses were powered, I look again, and it's B.I think the plane is smarter than you give it credit for (and smarter than any piece of software running on a desktop computer has ANY right being :()-Brian

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"Sorry, but the manual clearly states(11-8):The Pack controller logic will automatically change the pack control mode between each subsequent flight."Brian.... How does this differ from what I said?"And for that matter, how are you starting the aircraft that some buses come online and some don't? The aircraft is designed so that all 4 buses come on together unless circumstances prevent that."Dead ship... Battery On (Battery Bus powered), Standby Power on (Standby Bus powered), etc. ie. There is a certain bus power-up sequence. On some 744's, if you don't have the battery switch ON when applying external power to a dead ship, the SSB doesn't close. Etc.... "Also, I've found that the trigger is on landing, as the controllers switch over from A to B or back to A between when I'm on final and when I'm taxiing in. I have had ONCE a situation in which the previous flight had been A. I power up, and during that process, for some reason a couple of buses weren't powered (don't remember which ones) and it goes to A originally. Once all the buses were powered, I look again, and it's B."My statement about "A" being in command from a dead ship was taken straight from my manuals. I'll have a play with this system when I have the opportunity, and see if I can come up with an explanation for what we both are seeing. e.g. Dead-shipping for a certain amount of time may reset the system to "A", whereas short term power anomalies on certain busses may generate the situation you are seeing.Cheers.Q>

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Guest pilotbrian0

I'm curious, I've usually only turned on a pack AFTER providing power to all 4 buses. I know you can power a pack controller from the battery, but is it just "A" that can?What about the standby bus? If the standby bus is off, will the pack be powered? (IE, is it the standby bus, or the battery that the pack powers off when starting up?) What if i don't engage the battery, but connect EXT 2 (not 1, hypothetical)? Would only B work?I doubt PMDG modeled (if it's there in the real craft) some kind of "after so long, it defaults back to..." logic, as they probably didn't expect people to do what I typically do which is land, and then have the sim run through the full 2+ hour cool down/offload/onload turnaround period that happens after a trans-pacific flight (after 15 hours of flight time, that plane has definitely EARNED that break :()So: Here's the scenario that played out on my computer last night. I landed at KORD after a nearly 15 hour trip from VHHH. In flight, I had a pack controller A failure, so on landing I was operating B. When I shut down, it was on B. Completely shut down, I mean totally cold and dark (not even GPU connected). Maintenance did their "magic" and it was ready to fly again.I go in and power it up by turning on the battery, turning on the standby bus (no ground power, so no point turning on GPU). While maintenance worked I went and got food (sim sat for almost 3 hours, I talk a lot when I eat :() anyways, I turn on the bat, turn on the stby bus, and start the apu.Once hte APU was running, I turn on pack 2 and APU bleed. I checked the synoptic, and it said pack 2 was running off A. I powered up the main buses off APU 1 and 2 and look at the synoptic again, it said pack 2 was now running off B.Now, I'm not even going to try and guess what path the logic took there, as it was certainly muddled by the failure of controller A inflight the previous flight (it was A's turn, but A decided it didn't want to :() But it is curious that it knew to switch to B when it could.Now, the question is, and this is for PMDG or anyone who knows the REAL plane:In PMDG, is this the way it was intended?In the real plane, is this the way it works or does it do something different?I know, I'm still splitting hairs here, but when one gets a simulation like PMDG, they try to eke every ounce of realism out of it they can :D

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whats the point of flying without the autopilot? i cant imagine anything more boring that keeping it trimmed for a 5+ hour flight at cruise...

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Guest pilotbrian0

How about leaving it on autopilot for a 5+ hour flight at cruise?The plane I fly RW (small plane, I'll admit) has an autopilot. The autopilot came on ONCE when I was having radio problems, and I told the autopilot to fly at current altitude and heading while I figured out what was wrong. That's in roughly 100 hours of flight time, and I wouldn't have it any other way!-Brian

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"In the real plane, is this the way it works or does it do something different?"I'm sure someone at Boeing has the answer to this one. The manuals only give you the basics (need-to-know stuff).On the real aircraft it is not a good idea to mess around with AC Busses, switching them on and off. You tend to generate faults by doing this, so I probably won't find an answer to your questions anytime soon. Many airplane systems use more than one electrical bus, so you are making systems work in a way they weren't designed to operate (and could damage the systems as a result)."What about the standby bus? If the standby bus is off, will the pack be powered? (IE, is it the standby bus, or the battery that the pack powers off when starting up?) What if i don't engage the battery, but connect EXT 2 (not 1, hypothetical)? Would only B work?"REAL packs are NOT designed to be run without main AC/DC power. However, Boeings (767, 777, 744) vary in the way they react to electrical power loss. On a fully powered 744, you can turn on the packs, then shut down the electrical system and, assuming you still have a source of bleed air to drive the packs*, the packs will still continue to run, BUT you could damage the pack because you have depowered your pack protection circuits.*Note: The 744 APU requires the Battery to run.Even if I went to the effort of experimenting with the Pack Temp Control system, there is no guarantee that one airline's 744 will behave exactly the same as another airline's 744 (or for that matter, one aircraft behaving the same as the next aircraft). Airlines usually acquire the aircraft for their 744 fleet over a period of many years, so you are bound to get variations (modifications, upgrades, etc). PMDG, on the other hand, has only one or two versions (but that is not to say that they won't react differently in the environments (computers) in which they are placed).Yes, there are differences between PMDG and reality. I wouldn't fret over it however ;) I don't think you'll find RW pilots overly concerned about which controller is in command of a particular pack, just as long as there is ONE in command.Cheers.Q>

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Guest pilotbrian0

"I don't think you'll find RW pilots overly concerned about which controller is in command of a particular pack, just as long as there is ONE in command."Well, generally speaking, the language of pilots is filled with, "If it's working DON'T TOUCH IT!" :(So yeah... Like I said, I'm not overly concerned, I just want to establish in my sim as realistic operations as possible, and this is one area I have been unable to develop a "appropriate" procedure for, as I did not know what caused what. Now I know what causes it, in this sim aircraft, and have developed procedures for it.-Brian

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