# How to Calculate The Top Of Climb/Cruise Altitude?

Actuly(sorry spelling) I would like both! As I said,I’m a math freak.

I made an equation out of it, since you like math ;)

GS is Ground Speed
CRZ is Cruise altitude
VS is Vertical Speed

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And for cruise altitude?(I’ll give ya time;)

Are you asking how to work out what cruise altitude you should use for a route?

not for a certain route.

Roughly speaking:

Cruise FL = Trip distance (nm) e.g. for 60 nm flight optimum is FL060

Once you go above distances of 250 nm you can just head up to somewhere in the region of FL300-400.

This will also help.

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And for cruise altitude, it’s basically as high as you can, below service ceiling. This is to ensure the highest fuel efficiency possible. IRL it would be given to you by either your FMC/MCDU, by ATC, or by your airline.

I didn’t know exactly how to calculate it, but I found this. Enjoy.

The higher you fly (in the troposphere) the colder the air is, which makes the thermodynamic cycle of all air-breathing engines more efficient. Also, the air gets thinner, so your friction drag is reduced at the same TAS. The specifics depend on the thrust over airspeed, and generally you want to fly at a lift coefficient between

and

where cD0 is the zero-lift drag and AR the wing’s aspect ratio.

The higher value is perfect for piston engines and props, and the lower one for turbojets (think fighter aircraft engine). With a turbofan you will be between both values. To yield more precise results, both formulas will be longer, but these are the major factors for optimum lift coefficient.

Since there is an optimum cl for maximum range, you might want to climb continuously during the flight to compensate for the lower mass (due to fuel burn) with lower air density, so in reality you adjust altitude in steps, in accordance with traffic control.

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So I calculated a ToC of GS as 220 CRZas 12000 and VS as 1800. I got 23.9. Is this correct?

Also, 125 x fpl distance gives a reasonable cruise altitude.

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Oh,thank you man,but I am the age of 12, So my math-Knowledge goes as far as 7th grade. Like I said I love math,but im not that far into it yet. Could you simpliify?[quote=“Mats_Edvin_Aaro, post:13, topic:73128, full:true”]
And for cruise altitude, it’s basically as high as you can, below service ceiling. This is to ensure the highest fuel efficiency possible. IRL it would be given to you by either your FMC/MCDU, by ATC, or by your airline.

I didn’t know exactly how to calculate it, but I found this. Enjoy.

The higher you fly (in the troposphere) the colder the air is, which makes the thermodynamic cycle of all air-breathing engines more efficient. Also, the air gets thinner, so your friction drag is reduced at the same TAS. The specifics depend on the thrust over airspeed, and generally you want to fly at a lift coefficient between

and

where cD0 is the zero-lift drag and AR the wing’s aspect ratio.

The higher value is perfect for piston engines and props, and the lower one for turbojets (think fighter aircraft engine). With a turbofan you will be between both values. To yield more precise results, both formulas will be longer, but these are the major factors for optimum lift coefficient.

Since there is an optimum cl for maximum range, you might want to climb continuously during the flight to compensate for the lower mass (due to fuel burn) with lower air density, so in reality you adjust altitude in steps, in accordance with traffic control.
[/quote]

Is this a efficent(sorry spelling) calculation? I will bbl.

THAT, is a good thumb rule.

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Climb until ya’ stall:)

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Your “divide by 3” rule should be replaced by this for the most accurate calculation:
Divide by pi, raise to exponent e and take the square root.

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Another example of Andrew thinking he’s funny.

Wow lots of different and complicated ways of computing this!!

I like to keep it simple and through this forum have found these two simple formulas!

CRUISE HEIGHT

Total Distance / 7 = Flight Level.

Eg 240/7= 34 = FL340.

TOP OF DESCENT

FL / 3 = Distance To Go ( DTG) when to start your descent

eg FL340 / 3 = 113 nm.

Above are a rule of thumb and need to be adjusted for aircraft weight, traffic conditions etc but works in most cases!

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1. WMKK-WSSS TOTAL DISTANCE = 200 nm
200/7= 28.57= FL290
2. CALULATE TOD*
FL290
290/3 = 96.6
Start your descent when 97 nm from dest.
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Spot on there!

Keeping it simple. Like.

Thanks,Ya’al! See ya flying sometime.(Maybe)