ISA deviation
Thread Starter
Joined: Apr 2006
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From: Leicestershire
ISA deviation
I'm currently studying for exams upcoming in feb and i'm going through questions to try and get it all stuck into my head firmly, since i didnt do much in the past week of christmas my brain doesnt seem to function anymore (too much drink) and i cant find the answer i need anywhere, so i was wondering if anyone could post up how to find out ISA deviation at a given FL and also the formula for NAM and NGM.
Thanks
Thanks
Joined: Oct 2002
Posts: 96
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From: In transit
Hi,
Not sure this is what you're asking for but for the ISA deviation, take the Temperature given and the Flight Level, lets say -45°c and FL350
What you do is this:
Surface T° is 15°c decreasing 2°/1000ft, ISA T° at FL350 is therefore 35x2=70° - 15°= -55°c
So in this example we are ISA +10°c.
For NAM/NGM:
NAM= TAS*(NGM/GS), just remember that NAM/TAS=NGM/GS
There is also NGM = NAM +/- [(Wind speed*Time)/60]
Voilà
I hope this is what you asked for
J
Not sure this is what you're asking for but for the ISA deviation, take the Temperature given and the Flight Level, lets say -45°c and FL350
What you do is this:
Surface T° is 15°c decreasing 2°/1000ft, ISA T° at FL350 is therefore 35x2=70° - 15°= -55°c
So in this example we are ISA +10°c.
For NAM/NGM:
NAM= TAS*(NGM/GS), just remember that NAM/TAS=NGM/GS
There is also NGM = NAM +/- [(Wind speed*Time)/60]
Voilà
I hope this is what you asked for
J
Joined: Oct 2002
Posts: 96
Likes: 0
From: In transit
you're always given a starting point in the questions, if nothing is mentionned you assume ISA conditions and you start from 15°c at ground level and decrease every 1000ft.
Now if the temperature is let's say -23°c @ 22000ft and you have to work out the t° @ FL390, you start from -23°c and substract 2°c /1000ft up to the right level.
Bare in mind not to go lower than -56.5°c (if in the Gen Nav or Instrumentations exams for example), i.e. if they tell you the t° @ FL250 is -40°c and ask for t° @ FL390, it's going to be -56.5°c, not less
. I remember a couple of questions like that during these exams
Mcgoo,
They have removed the formulas for NGM in the new CAP edition, I know as I have it in front of me for my Flight Planning exam
Happy New Year!
Now if the temperature is let's say -23°c @ 22000ft and you have to work out the t° @ FL390, you start from -23°c and substract 2°c /1000ft up to the right level.
Bare in mind not to go lower than -56.5°c (if in the Gen Nav or Instrumentations exams for example), i.e. if they tell you the t° @ FL250 is -40°c and ask for t° @ FL390, it's going to be -56.5°c, not less
. I remember a couple of questions like that during these examsMcgoo,
They have removed the formulas for NGM in the new CAP edition, I know as I have it in front of me for my Flight Planning exam
Happy New Year!
Joined: Oct 2005
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From: uk
Thread Starter
Joined: Apr 2006
Posts: 60
Likes: 0
From: Leicestershire
thanks for the help, i'll be sure to have a read through the cap, i would never of spotted that if someone didnt point it out, I'll have to find the question where you needed to calculate the isa deviation, i'm sure it didnt give you a start temp, maybe it's the drink i better lay off it for a while.
Thanks for the help
i better lay off it for a while. Thanks for the help
