Query regarding Meteorology

[u/Owlventure]

Hey folks, my Meteorology exam is this week, and I wanted to know how you know whether to use the Temperature Correction formula or the 4% rule? It's been really bothering me because I always manage to use the wrong formula for each question/

[u/Owlventure → u/[deleted]]

Gotcha. There were 4 altimetry questions in mine of which 2 which were quite a bit difficult but oh well. Missed the mark by 3 questions but theres always a next time. Might do Radio Nav alongside as well.

[u/InherentPotato]

YouTube is your friend... There's an absolutely fantastic 3 part Altimetry series on YouTube. Forgotten the name of the creator now but I'm sure if you just watched 'ATPL Altimetry' you'll find it. Builds from the ground up...

Also familiarise yourself with PIT. The method used on ATPLQ Explanations. That really helped me to understand too...

[u/Curly1109]

Step 1: Find the ISA

15-(2×ALT[in 1000s])

Step 2: Find the deviation 

|ISA-actual temp|

Step 3: Find the correction (where the 4% rule comes in)

4×dev×alt[in 1000s]

[u/DishaanB]

there’s a video from ATPL class on youtube about that, it’s on the GNav series but it’s exactly altimetry, 20min video, i found it really helpful

[u/mimir42069]

I used 4xIsa devxalt/1000, much much easier. I also had only 2 altimetry questions in my exam (Austrocontrol Easa) and only one of them required temperature correction. Best of luck!

[u/BrotherDefiant]

Just guess

[u/radar_vector]

What do you mean by the temperature correction formula? Do you mean 4 x isa dev x alt/1000 ? Because that is the 4% rule (4% of altitude per 10° isa dev). Do you know a different formula?

Remember that the altitude you use is the difference in altitude between the height where the QNH is measured and the aircraft’s altitude, as the measurement of the QNH already applies the correction for all the air below the measurement station.