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Rockliffe

How high do I fly?

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OK, I'm sure this is a question I should know the answer to, but to be honest, there are quite a few questions that I should know the answer to but don't! So, when I'm creating a flightplan, how do I calculate the best, or optimum, altitude to fly. Help as always appreciated, cheers fellas.

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Take into account East or West travel, IFR or VFR, winds, trip duration, and terrain/obstacles.

 

You'll get better fuel consumption higher up, usually.

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Mmmm, sure, but is there not some kind of calculation that determines the optimal height. eg, if I'm flying from point A to point B and the distance is only 80 miles then how high do I fly? It is unlikely to be above 20,000ft so...?? Should it be 15,000ft or maybe 12,000ft? Sure, if it's 1,000 miles I can safely say I'll fly at flight level 320 or am I missing something?

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Howard,

 

It also depends on the type of aircraft being flow. Lets take a piper seminole for example (I am very fimiliar with this twin from real world experience), I am going to fly as high as practical up to around 10,000ft since it is not pressurized. Take into account that I am IFR and going eastbound this will get us 9k, 7k, or 5k. Then I am going look at the winds to see which is the most favorable, Lets say 5 and 7k are favorable. I will end up flying at 7k if the route is long enough or 5k if it is a short hop.

 

With jets, the higher you are the better fuel economy youy will get. I am not sure if there is a forumla for optimum climb times but I typically start my flight planning at FL280 since I fly short regional jet ops and work up from there paying attention to winds/icing/direction of travel and so on.

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Thanks for the reply Tom. I should actually have mentioned that I am talking about flying liners rather than GA. While I understand with GA I don't see an issue, it's just when creating an actual flightplan beforehand with say the NGX. So from what you've said, there doesn't seem to be any particular formula for determining the altitude with the ascent/descent rate and distance. It seems odd though... I mean the height to fly will be different on a 100 mile flight than a 400 mile flight, and how would you determine that at the flightplanning stage? If it was a 1000 miles, as I said, you could safely create a plan cruising at FL320 or similar, couldn't you? Or am I simply making things more complicated than they really are?

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Hi!

 

I'm only a sim flyer so I can't really give you info exactly like in the real world but I can mention a few things I do which help me choose a cruise altitude.

 

1. Find a real world flightplan for the flight (if you're interested in that option):

 

Good sites are:

www.Flightaware.com

www.Simroutes.com (for the US mainly)

The Euroute database (for Europe mainly)

The Avsim flightplan forum.

 

In many cases these will have real world cruise altitudes/flight levels used by real airlines on these flights. From my experience at least in Europe some of them go suprisingly high even on shorter sectors (like Ryanair 737's flying at FL380). They also sometimes post step climbs for medium and long-haul flights too which is good.

 

2. If I'm not using a real flightplan I just pick anything. Normally for 737 flights of an hour or two this is between FL300 and FL400. I think FL310,330,350,370 etc. are for West-East and FL300,320,340,360 etc. are for East-West but I'm kinda unsure. If it's a shorter flight like London-Manchester or London-Paris then I use the 1:3 rule. You multiply by 3 so say getting to 30,000ft will take 30x3 which is about 90 or roughly 100 miles. So 100 miles to get up there and 100 miles in descent would probably be fine for a 280 mile trip or something. It's nice to be in cruise for a little time rather than just going up or down for the whole flight!

 

Anyway I'm no real pilot so I'm sure others can give better info but thought I'd mention the couple of simming things I do!

 

Many thanks,

 

Pierre

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Everything in the jet world is based on fuel economy. With that said, with real world ops, what you file may not be what you are assigned. If your flying the NGX you have GPS and won't be paying much attention to the MEA for navigation reception. GPS gives you more flexibility for altitudes since you can also go "off-route" as in off of a jetway, this allows for more aircraft to fly the same altitude. If your taking a jet route that is highly populated ATC may give you a different altitude for traffic avoidance.

 

I do not have the NGX (please don't hate me) but those that do can chime in on climb performance and I am sure there's not too much of a time difference from climbing extra 4 or 5 thousand feet. Keep in mind that with pax your also looking for the best ride so if FL360 offers the best ride and FL380 the best economy by a few minutes, you may file 360 to give the guys in the back paying the fuel bill the best ride.

 

Hope this also helps.

 

You also are not alone in 121 operations, you always will have a dispatcher to figure this stuff out.

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80 flying miles in the 737 NG... I probably wouldn't go much higher than 14,000... and if you're full of pax you probably won't go higher than 10,000

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80 flying miles in the 737 NG... I probably wouldn't go much higher than 14,000... and if you're full of pax you probably won't go higher than 10,000

 

I would be above 10k at least, that way I can go fast.

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I think Tom's replies are probobly the best if you are "hardcore" (ie trying for realistic ops). Also, yes you would have a pre made flight plan in the RW.

 

For me, its Flightaware. I did some short hops in the new Avro RJ today and this is how they went:

For EWR to AVP in the Avro RJ, I used 6k for the 80 mile cruise. There was no Flightaware route of a comparabe aircraft so i had to flat out guess.

For the flight from AVP to BOS (FL180) then BOS to EWR (FL160) I looked up some flights on flightaware and went with those.

 

For longer flights I also take into account the GW. if you've flown your addon aircraft at different weights, then you have an idea of what time of climb performance you should expect. A fully loaded (addon aircraft) usually sucks wind as you get near it's service ceiling. So in some instances, a multi step cruise plan would help as well

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I would be above 10k at least, that way I can go fast.

 

Yep I agree... that's why I wrote 10... the magic number in the US...

 

Since Howard is flying in the UK and I don't know their rules... I'd still think 100-140 for a cruise altitude.

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I used to fly BWI-RIC, which is about 120 mi...generally topped off at 20,000 feet in an A320. Any higher was just plain useless--I once tried 30,000 and was told to descend before I reached it. For 80 mi I would recommend around 15,000-18,000.

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Rockliffe, if your flying the NGX and program your route including the SID and expected STAR, when you go to set the cruise altitude, the FMC will display the optimal cruise altitude based on the distance of your route, weight of the a/c at the time, etc. You can then use that as a guide.

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Yep I agree... that's why I wrote 10... the magic number in the US...

 

Since Howard is flying in the UK and I don't know their rules... I'd still think 100-140 for a cruise altitude.

 

If you're out in the sticks with no one around you can always ask ATC for "high speed" below 10k, the 747s always ask for it (and they usually get it) because full manoeuvring margin is only available at or above Vref+100, which can be above 250kts for a heavily loaded 747.

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If you're out in the sticks with no one around you can always ask ATC for "high speed" below 10k, the 747s always ask for it (and they usually get it) because full manoeuvring margin is only available at or above Vref+100, which can be above 250kts for a heavily loaded 747.

 

This rarely if ever happens, the atc wont let you break the rules just because you don't want to fly with your flaps down for a few minutes.

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Also Howard,

Enter your airports in "Top Routes" on the link below and use the routes and look at the ALT, but like above always look what the FMS ALT gives as the best. If you use a flight with a FL320 and your FMC says FL280, when using FSX ATC just ask for a different ALT you have to ask for decent by XXXXXft.

http://www.vataware.com/index.cfm

 

BTW old friend I thought you might have seen my post you know where?

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Also Howard,

Enter your airports in "Top Routes" on the link below and use the routes and look at the ALT, but like above always look what the FMS ALT gives as the best. If you use a flight with a FL320 and your FMC says FL280, when using FSX ATC just ask for a different ALT you have to ask for decent by XXXXXft.

http://www.vataware.com/index.cfm

 

BTW old friend I thought you might have seen my post you know where?

 

Hi Dave, good to hear from you, thanks for the info. erm BTW old friend I thought you might have seen my post you know where? ??

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From the charter work I do, i use the general rule of thumb. Take the distance and add 2 zeros up to a few thousand below your service ceiling. ex 250NM trip = FL250. If you go above this you are usually climbing to your cruise altitude then almost immediately descending for your intended approach(IFR).

 

 

This rarely if ever happens, the atc wont let you break the rules just because you don't want to fly with your flaps down for a few minutes.

 

Dude in canada this happens all the time, its not breaking the rules but more an exception. The other thing is Air Canada almost always flys 250-300knots below 10,000ft and tells Center that they are holding 250(buddy is a 25 year veteran ATC at YWG ACC).

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I think the OP might be asking if there is an algorithm for a jet airliner that could be applied, with flight distance being the input variable and cruise altitude being the output, that would allow for:

- Climb with VNAV (assumed optimum rate of climb/ airspeed) to cruise alt

- Cruise for a minimum of 30 minutes

-Descent with VNAV (optimum descent rate to HAA of 2,000 feet

- Slow to VRef + 20

-Cross FAF, 2,000' HAA

 

There will be a critical number for "distance" that above which "altitude" will be capped at service ceiling, and (as othes have posted here) wind, weight and cost index might dictate the desired altitude. Below the critical number of "distance", service ceiling is not attainable in the distance, and regardless of all other factors, max altitude is governed primarily by distance.

 

Of course, the equation above would change radically for different categories of aircraft, although I would think that most pax jets could be separated into "light" or " heavy" and should be similar within their respective categories. What I might suggest is several flights of less than 1 hour duration and note the recommended altitude in the Perf Init screen, and make up a table.

 

Thanks, Bruce.

 

 

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From the charter work I do, i use the general rule of thumb. Take the distance and add 2 zeros up to a few thousand below your service ceiling. ex 250NM trip = FL250.

 

That's what I wanted! Thanks, a godd tip...

I think the OP might be asking if there is an algorithm for a jet airliner that could be applied, with flight distance being the input variable and cruise altitude being the output, that would allow for:

- Climb with VNAV (assumed optimum rate of climb/ airspeed) to cruise alt

- Cruise for a minimum of 30 minutes

-Descent with VNAV (optimum descent rate to HAA of 2,000 feet

- Slow to VRef + 20

-Cross FAF, 2,000' HAA

 

There will be a critical number for "distance" that above which "altitude" will be capped at service ceiling, and (as othes have posted here) wind, weight and cost index might dictate the desired altitude. Below the critical number of "distance", service ceiling is not attainable in the distance, and regardless of all other factors, max altitude is governed primarily by distance.

 

Of course, the equation above would change radically for different categories of aircraft, although I would think that most pax jets could be separated into "light" or " heavy" and should be similar within their respective categories. What I might suggest is several flights of less than 1 hour duration and note the recommended altitude in the Perf Init screen, and make up a table.

 

Thanks, Bruce.

 

Cheers Bruce, yes, I was after some kind of formula, but what has been suggested above is a good guideline, thanks...

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+1 to sgtscarfy

Anything less than 300 miles use the distance for the altitude, eg.

For 80nm use 8000ft (if westbound, I would use 9000ft for eastbound) and so on...

Dan

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