ECON CRZ, page 2/3

[Wennerholm 44]

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?

[Captain Kevin 586]

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.

[Wennerholm 44]

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?

[Captain Kevin 586]

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.

[downscc 1,327]

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.

[Wennerholm 44]

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

[Wennerholm 44]

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.

 

[downscc 1,327]

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.

[Wennerholm 44]

   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

 

 

[thibodba57 462]

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.

 

[Captain Kevin 586]

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.

[Wennerholm 44]

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.

[youngie63 4]

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?

 

[Captain Kevin 586]

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.

[downscc 1,327]

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.