Trip distance vs cruising alt: is there a rule of thumb?
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Trip distance vs cruising alt: is there a rule of thumb?
Now that i'm moving from spamcans into the world of larger aircraft that require descent planning,etc i would like to know if there is a formula or rule of thumb for roughly calculating the max altiude for short legs. I'm aware that larger ac have tables i their manuals to be used for flt planning.
What i mean is while FL350 might be ok for a 300nm flight it might be too high for a 100nm leg.
Thanks
What i mean is while FL350 might be ok for a 300nm flight it might be too high for a 100nm leg.
Thanks
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Wouldn't that be dependant on the enroute MEA's MOCA's ? and for that matter your companies Perfromance section which is where all the flight plans and cruise levels are decided .....will decide whats the best level for any given distance taking into consideration both time and feul burn ........
typically there is no rule of thumb to a FL however if u wanna know about descent planning from ny level the rule of thumb that works everytime and gets your a/c on profile ... is
FL into 3 + - 10 for wind should get you there everytime !
eg : If your cruising at FL 350 den multiply this fig by 3 + 10 depending on wind which is at what distance you would have to ask the boys at control to descend !
typically there is no rule of thumb to a FL however if u wanna know about descent planning from ny level the rule of thumb that works everytime and gets your a/c on profile ... is
FL into 3 + - 10 for wind should get you there everytime !
eg : If your cruising at FL 350 den multiply this fig by 3 + 10 depending on wind which is at what distance you would have to ask the boys at control to descend !
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The rule of thumb depends on your typical rate of climb, rate of descent, and how long you want to be level in the cruise - you will have some minutes climbing, some minutes cruising, and some minutes descending.
In our case, we climb and descend at 2000 fpm at lower levels (the rate reduces in the 20's), and I like at least 5 minutes in cruise so that I can do the paperwork and brief the approach.
So, for a trip that will take 20 minutes, we'd be prepared to go to FL150 (which we would reach in 7 1/2 minutes of climbing). For a trip that takes 30 minutes we'd go as high as FL250. After that the rate of climb gets more complicated, so levels after that get more cautious, but you get the idea. Note that the reality will need to factor in ATC restrictions, step climbs and so on, but the principle works.
In our case, we climb and descend at 2000 fpm at lower levels (the rate reduces in the 20's), and I like at least 5 minutes in cruise so that I can do the paperwork and brief the approach.
So, for a trip that will take 20 minutes, we'd be prepared to go to FL150 (which we would reach in 7 1/2 minutes of climbing). For a trip that takes 30 minutes we'd go as high as FL250. After that the rate of climb gets more complicated, so levels after that get more cautious, but you get the idea. Note that the reality will need to factor in ATC restrictions, step climbs and so on, but the principle works.
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And don't forget ATC restrictions... for example we limit some short-haul flights to FL245 over the London area - keeps up top free for the big heavy things flying a lot further.
Capt Manuvar,
The short answer to your precise question is yes, a rule of thumb does exist. Here it is:
**The distance to be flown in nautical miles divided by ten equals the maximum altitude in thousands of feet to plan for shorter trips.**
In jets, this seems to work out best on segments of between 200-300 nm. Outside this range, other considerations (some of which are mentioned in previous posts) often dictate that a different altitude be selected. This formula may be used as a starting point in short range altitude planning and should be adjusted after due consideration of the many factors that should influence your selection of an enroute cruise level.
The short answer to your precise question is yes, a rule of thumb does exist. Here it is:
**The distance to be flown in nautical miles divided by ten equals the maximum altitude in thousands of feet to plan for shorter trips.**
In jets, this seems to work out best on segments of between 200-300 nm. Outside this range, other considerations (some of which are mentioned in previous posts) often dictate that a different altitude be selected. This formula may be used as a starting point in short range altitude planning and should be adjusted after due consideration of the many factors that should influence your selection of an enroute cruise level.
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Another method:
1/2 the total track miles and multiply by 3.
e.g. 100nm equates to FL150.
This usually gives around 1-3 minutes at cruise. Boeing look at optimum cruise level as spending at least 1 minute at cruise.
1/2 the total track miles and multiply by 3.
e.g. 100nm equates to FL150.
This usually gives around 1-3 minutes at cruise. Boeing look at optimum cruise level as spending at least 1 minute at cruise.
<<I consider 10% of the trip length and add 5:>>
LearjetGA,
I like that alot. I will use it whenever I am flying out of an area where you can expect no climb delays or early descents from ATC. Thanks,
WH
LearjetGA,
I like that alot. I will use it whenever I am flying out of an area where you can expect no climb delays or early descents from ATC. Thanks,
WH
