K Wennerholm

ECON CRZ, page 2/3

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Hi! When input FL340 in FMC the CRZ LEG's shows FL410. In ECON CRL page 2/3, CRZ ALT, I find STEP TO FL410. Can anyone here explain why? When I change STEP TO, the LEGS change to. My aircraft follow STEP TO FL410 if I not change the value. Are there a TRIM digital display in the B747 like in the B777?

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What does it say for step size. The STEP TO is basically telling you the altitude in which you'd perform your next step climb and then it would tell you how far you'd have to fly before you were able to make the climb. The reason is that jet engines are more efficient at higher altitudes, but if you're heavy on departure, you might not actually be able to climb that high. You'll climb to a lower altitude, say flight level 300, burn off fuel, then climb to flight level 320, burn off fuel, then climb to flight level 340....I think you get the picture. The fact that you have your cruise altitude set to flight level 340 and the step climb telling you your next altitude is flight level 410 leads me to believe you have a rather unusual step size. Of course, a screenshot of what you're seeing would definitely help.

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Just now, Captain Kevin said:

What does it say for step size. The STEP TO is basically telling you the altitude in which you'd perform your next step climb and then it would tell you how far you'd have to fly before you were able to make the climb. The reason is that jet engines are more efficient at higher altitudes, but if you're heavy on departure, you might not actually be able to climb that high. You'll climb to a lower altitude, say flight level 300, burn off fuel, then climb to flight level 320, burn off fuel, then climb to flight level 340....I think you get the picture. The fact that you have your cruise altitude set to flight level 340 and the step climb telling you your next altitude is flight level 410 leads me to believe you have a rather unusual step size. Of course, a screenshot of what you're seeing would definitely help.

Hi, Kevin! I will take a look at the step size in my flight later today. I going to send you a screen shot. Can you give me your email. I do not know how to publish a screenshot here at  AVSIM. Do you know what is AVSIM an abbreviation for?

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Just upload it to a photo hosting website like Imageshack or something and post the link here. I have no idea what AVSIM stands for if it stands for anything at all, but my guess would be on AViation SIMulation. That's just a guess, mind you. I could be completely wrong.

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More likely explanation is that FL340 is much too low for his weight so as soon as he reaches TOC he is already at SC and since he is probably light he is going all the way up.

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Just now, downscc said:

More likely explanation is that FL340 is much too low for his weight so as soon as he reaches TOC he is already at SC and since he is probably light he is going all the way up.

My TOW=255,6 Kg

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Just now, Captain Kevin said:

Just upload it to a photo hosting website like Imageshack or something and post the link here. I have no idea what AVSIM stands for if it stands for anything at all, but my guess would be on AViation SIMulation. That's just a guess, mind you. I could be completely wrong.

Her comes the pic of my CDU according to our agreement later today. I have changed the value from 410 to 350 FYI.

 

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Cruise ALT of FL345 is very odd... why that value?  Why the step climb?  AVSIM is the name of this forum that is hosting the PMDG subforums.

Have you flown the Tutorial?  If you are new then it is going to seem like drinking from a fire hose.  Start with the Tutorial then ask questions about it.

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   Yes, I have fly the tutorial with the same result. The step climb is a problem. Can I just delete it in FMC? The Tutorial does not concern about step climb at all. Pleas tell me how to select/calculate Cruise ALT. What kind of parameters determines the CRZ Alt? Now I only select a value without a logical background

 

 

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Just quickly reading this.  Sounds like your wondering why the plane is planned. Step climb automatically and you don't want it to.  It's it's telling you to Step higher than programmed because on the PERF INIT page you left Step at ICAO.  Put 0 in 6R and you won't have any programming issues anymore.

 

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1 hour ago, Ken Wennerholm said:

   Yes, I have fly the tutorial with the same result. The step climb is a problem. Can I just delete it in FMC? The Tutorial does not concern about step climb at all. Pleas tell me how to select/calculate Cruise ALT. What kind of parameters determines the CRZ Alt? Now I only select a value without a logical background

Okay, so there are many factors that determine what cruise altitude you should select. One of the first is direction of flight. If you're flying west, you'll fly at an even altitude, like flight level 340 or 360. If you're flying east, you'll fly at an odd altitude, like flight level 350 or 370. The fact that you've selected flight level 345 is highly unusual. The next thing to take into consideration is the weight of the aircraft. You really do need to plan your flight and look at the charts in order to figure this out, but if you want to do it the quick and easy way, just pick one (it won't matter at this point since you'll change it anyway, but you need to punch something in for the FMC to do its calculations), then go to the cruise page, which is the page you're already looking at in the screenshot you posted. You will see your optimum altitude is flight level 376 and your maximum altitude is flight level 408. You want to be as close to optimum as possible, so in this case, if you were flying west, you would select flight level 380. If you were flying east, you would select flight level 370. Right now, your step size is showing as ICAO, but in normal circumstances in RVSM airspace, it's generally 2,000 feet, so you'd want to punch in 2000. When you've done all that, the STEP TO should then show you what your next step climb altitude is and how far you have to fly to get there. If you've done everything I've just said, your next step climb altitude should be flight level 400 or 390, depending on if your initial altitude was 380 or 370.

Now what if your flight was running north and south. Between heading 000 and 179, you'd be considered flying east, so you'll use an odd altitude. Between heading 180 and 359, you'll be considered flying west, so you'll use an even altitude. Hope this helps.

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9 hours ago, Captain Kevin said:

Okay, so there are many factors that determine what cruise altitude you should select. One of the first is direction of flight. If you're flying west, you'll fly at an even altitude, like flight level 340 or 360. If you're flying east, you'll fly at an odd altitude, like flight level 350 or 370. The fact that you've selected flight level 345 is highly unusual. The next thing to take into consideration is the weight of the aircraft. You really do need to plan your flight and look at the charts in order to figure this out, but if you want to do it the quick and easy way, just pick one (it won't matter at this point since you'll change it anyway, but you need to punch something in for the FMC to do its calculations), then go to the cruise page, which is the page you're already looking at in the screenshot you posted. You will see your optimum altitude is flight level 376 and your maximum altitude is flight level 408. You want to be as close to optimum as possible, so in this case, if you were flying west, you would select flight level 380. If you were flying east, you would select flight level 370. Right now, your step size is showing as ICAO, but in normal circumstances in RVSM airspace, it's generally 2,000 feet, so you'd want to punch in 2000. When you've done all that, the STEP TO should then show you what your next step climb altitude is and how far you have to fly to get there. If you've done everything I've just said, your next step climb altitude should be flight level 400 or 390, depending on if your initial altitude was 380 or 370.

Now what if your flight was running north and south. Between heading 000 and 179, you'd be considered flying east, so you'll use an odd altitude. Between heading 180 and 359, you'll be considered flying west, so you'll use an even altitude. Hope this helps.

Thank´s! You help me a lot! Now I going to practice.

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Hi Guys

I have no issues with the discussions to date, however when using a planning tool (Simbrief), it gives specific Step Climbs in total contrast to the FMC. At the moment I am doing YSSY-RPLL. Simbrief, using a TOW of 742,300 lbs, gives me a step climb of FL340 at DOLIB (890nm Syd) - that sounds about right to me given I'm a touch heavy and a further SC to FL360 2120nm Syd). However, the FMC gave me a SC to FL350 almost immediately after takeoff (Opt 339). (yes, I know its contrary to direction of flight)

It begs the question, are Step Climbs calculated during the flight planning phase, based purely on FMC calculations or a combination of both?

 

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7 hours ago, youngie63 said:

It begs the question, are Step Climbs calculated during the flight planning phase, based purely on FMC calculations or a combination of both?

I would think a combination of both. The FMC is going to calculate them based on the information you put in, so if you put in something non-standard, it's going to go off of that. At the same time, generally speaking, you'd plan it out before you got to the plane, so you would already know what initial cruise altitude should be.

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14 hours ago, youngie63 said:

when using a planning tool (Simbrief), it gives specific Step Climbs in total contrast to the FMC

This comes up often enough I think it might belong in the Introduction manual.  PMDG has programmed the FMC to provide a realistic simulation of the actual systems using Boeing performance data not available to hobbyists who are creating fine but non-professional applications that we have access to in the simulation world.  The guy that does this for PMDG has a PhD in Aerodynamics (or similar).  My money is on the FMC.  In the RW, you'll find licensed dispatchers working with professional and very complex systems that model each aircraft. It is a different world from the simulation world.  One more consideration is that you are not going to start your step climb regardless of flight plan or FMC without clearance from ATC.

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Thanks guys, pretty much confirmed what l thought. That said, if a captain decides to stick with the flight planned SC's, shouldn't he be able to manually program the FMC accordingly in the VNAV page E.g. at time 'xxxxz' climb to 'FLzzz' or at 'Wpt' climb to 'FLzzz'. Just curious as the PMDG FMC will allow some changes but not those specified in the examples.

 

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6 hours ago, youngie63 said:

Thanks guys, pretty much confirmed what l thought. That said, if a captain decides to stick with the flight planned SC's, shouldn't he be able to manually program the FMC accordingly in the VNAV page E.g. at time 'xxxxz' climb to 'FLzzz' or at 'Wpt' climb to 'FLzzz'. Just curious as the PMDG FMC will allow some changes but not those specified in the examples.

No, because you can't just change altitudes without getting approval from the air traffic controller. Yes, it might be in the flight plan, but what's planned and what actually happens are two completely different things. Once you get the approval to change altitudes, then you can punch in the cruise altitude on the cruise altitude line.

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8 hours ago, youngie63 said:

That said, if a captain decides to stick with the flight planned SC's, shouldn't he be able to manually program the FMC accordingly in the VNAV page E.g. at time 'xxxxz' climb to 'FLzzz' or at 'Wpt' climb to 'FLzzz'.

Hi,

You can enter manual stepclimb in the leg page by entering the three figures of the flightlevel followed by S (ex: 350S) but you'd better leave the steps calculated by the FMC. The step climbs of the flight plan are based on fuel consumptions and winds predictions. Shoud your fuel consumptions and winds be a bit different in the real flight and your theoretical step climbs from the flight plans won't be optimum while the FMC will update the calculations throughout the flight.

Keep it mind that the step climbs in the flight plan are just "advisory" with regards to the waypoints they are attached to. You don't have to execute them as per the flight plan, except for change of levels required due to changes of airways or airspaces.

Also as said by Kevin, no change of level is allowed without clearance from the ATC no matter what (except of course in case of TCAS alert).

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9 hours ago, youngie63 said:

Thanks guys, pretty much confirmed what l thought. That said, if a captain decides to stick with the flight planned SC's, shouldn't he be able to manually program the FMC accordingly in the VNAV page E.g. at time 'xxxxz' climb to 'FLzzz' or at 'Wpt' climb to 'FLzzz'. Just curious as the PMDG FMC will allow some changes but not those specified in the examples.

Trust the plane over the dispatch paperwork. That paperwork is a plan. It is not actuality. That plan could have been made hours before the flight, with weights that weren't adjusted (note the adjustment lines on all dispatch paperwork). The FMC will have the best performance data, so go with its step function, unless there is a specific reason to do otherwise (fixed cruise segment due to a NAT crossing, for example).

Don't overcomplicate the issue, either. Putting the altitudes in there is only relevant to getting a better idea of performance (specifically fuel burn), and again, only necessary if you know you will be forced into that altitude for some reason or another (NAT crossing, max altitude on an airway, and so on). The function is NOT to be used as a way of getting the plane to automatically climb (that isn't a function of the real jet anyway).

Short version: if you do not have some sort of altitude restriction, set the step size to whatever you need it to be and leave it alone. Don't overcomplicate it, as many simmers are apt to do when handed an FMC.

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My experience with dispatch is that they are pretty darn precise.  At least my airline releases are within an hour and the weights are given after pax are loaded and bags are scanned inside the aicraft.  If they are deviations, are usually for winds or reroutes.  There are manual dispatch weight adjustments, but they are given prior to takeoff and updated in the FMS.  Like anything, trust but verify, however dispatch is pretty darn good.

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11 hours ago, icaruss said:

My experience with dispatch is that they are pretty darn precise.  At least my airline releases are within an hour and the weights are given after pax are loaded and bags are scanned inside the aicraft.  If they are deviations, are usually for winds or reroutes.  There are manual dispatch weight adjustments, but they are given prior to takeoff and updated in the FMS.  Like anything, trust but verify, however dispatch is pretty darn good.

Agreed, but that's not the point. Don't force the plane into following the dispatch SCs simply to have it follow the dispatch exactly, unless, of course, there is a specific reason (those I mentioned earlier).

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Thoughts from me:

Generally I agree with Kyle. However, I know of at least one airline whose guidance to pilots was/is to stick to the OFP levels as they were planned for the optimum levels based on forecast winds (and, potentially, ATC restrictions etc) and therefore they considered them likely to be more accurate/efficient than the FMC overall. There is also an issue that at one point the CFMU types were getting cheesed off with pilots climbing as high as possible despite being flightplanned at lower levels and thus screwing up their flow management (because if you split a sector vertically based on a certain number of aircraft planned at a lower level and they all climb up in to the higher sector it ends up overloaded). In practice, regardless of the guidance I think most pilots just climb as high as they can as soon as they can (i.e. follow the FMC).

However, with Boeing Winds these days I think the quality of the FMC wind data is much better now and thus I think it provides better results. Thus -- yes, ATC permitting I would go with the FMC.

As mentioned above, what you should do if you know you are not going to be able to climb/will be required to climb at a certain point is enter that in to the FMC as this will improve your time/fuel predictions.

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1 minute ago, skelsey said:

Generally I agree with Kyle. However, I know of at least one airline whose guidance to pilots was/is to stick to the OFP levels as they were planned for the optimum levels based on forecast winds (and, potentially, ATC restrictions etc) and therefore they considered them likely to be more accurate/efficient than the FMC overall. There is also an issue that at one point the CFMU types were getting cheesed off with pilots climbing as high as possible despite being flightplanned at lower levels and thus screwing up their flow management (because if you split a sector vertically based on a certain number of aircraft planned at a lower level and they all climb up in to the higher sector it ends up overloaded). In practice, regardless of the guidance I think most pilots just climb as high as they can as soon as they can (i.e. follow the FMC).

All of these would classify as:

"unless, of course, there is a specific reason (those I mentioned earlier)."

...so, I'm confused as to why we're continuing down this path.

 

 

If there is a reason that you are going to do X. Do X. It is also advisable to let the aircraft know that you are doing X.

If you're looking at a default PFPX plan, though, and it simply shows it expects you'll probably be at X altitude by Y point, and throws in an advisory altitude/speed in the OFP, and you have no idea why it did that - go with the flow, and don't overcomplicate things.

There are people up front because we have yet to substitute computers for brains. Use your brain. "Will this help me, and is this necessary?" Look at some of the odd stuff PFPX will toss into a plan. Some people do 42 backflips, 10 pushups, and finish by bobbing for apples, just to get the FMC to match that plan (that makes little to no sense). There's no need. "Does this make sense? Is it telling me to be at X altitude for a specific reason other than the assumption of the normal FMC step profile? Yes? Okay, mod the data. No? Okay, leave it alone."

It's really, actually, incredibly simple. The problem is that real world dispatch is usually manually setting those params, or they're using more powerful planning tools for optimization. PFPX is limited to the user, and most people don't even know you can set segment restrictions (like across the NATs), but people trust the program as if it were a human doing it. Wrong.

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Sure. As I say, I'm not disagreeing with you -- if the wind data is accurate (as it is now IRL, more so than in the past, with AOC Boeing Winds uplinks) then the FMC is an excellent tactical tool. Just throwing in some additional background as to why sometimes it might be appropriate to follow the OFP (or indeed why "XXX pilot says we're supposed to follow the OFP...") or why it might not be, or indeed why it might not be appropriate to follow either if you look at the wind forecast/hear from another aircraft that there's a whacking great headwind or turbulence at FLxxx.

PFPX and Simbrief can (and do) optimise levels based on the wind forecast etc (though the PFPX optimisation in particular I find rather odd).

31 minutes ago, scandinavian13 said:

There are people up front because we have yet to substitute computers for brains. Use your brain.

Absolutely. However, to make the best decisions it's necessary to understand how the system(s) (both on the planning side and the aircraft side) work and how they are arriving at their numbers.

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PFPX vs a real world dispatch software operated by a certified dispatch are two completely different scenarios.

Anyways, bottom line is a release gives you a good plan to follow, unless it warrants a deviation by the pilot, due to different conditions from those planned.  Commonsense really by the pilot is the rule of thumb.  

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