Cold weather altimetry & seasonal changes to minimum altitudes
Joined: Nov 2002
Posts: 229
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From: Hogwarts
One popular misconception is that a lot of people think that they need to apply the temp correction directly to their ALTITUDE. It is the HEIGHT above the aerodrome where the QNH or QFE is measured that needs correcting.
On the ground at the ARP our altimeters should read APT elevation with aerodrome QNH set whatever the temperature. In ISA a CAT1 DA (with 200'DH) for an airport of 2000' TDZE would be 2200'. If it was -20C you would increase the DH to 230' so the DA becomes 2230'. The marker HEIGHT of say 1500' would be adjusted up to 1700' giving a marker crossing ALT of 3700' etc.
It looks like the temperature correction issue needs to be standardised worldwide. In the UK we also have to consider the extremes like -20C in Inverness (and -20C in London in 1981).
If mountains were compressable like air there would be no problem.
On the ground at the ARP our altimeters should read APT elevation with aerodrome QNH set whatever the temperature. In ISA a CAT1 DA (with 200'DH) for an airport of 2000' TDZE would be 2200'. If it was -20C you would increase the DH to 230' so the DA becomes 2230'. The marker HEIGHT of say 1500' would be adjusted up to 1700' giving a marker crossing ALT of 3700' etc.
It looks like the temperature correction issue needs to be standardised worldwide. In the UK we also have to consider the extremes like -20C in Inverness (and -20C in London in 1981).
If mountains were compressable like air there would be no problem.
Joined: Jul 2002
Posts: 39
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From: Earth
In Finland we easily get temperatures -10 celsius and below during winter.
If this is the case, during vectoring radar clears "descend to 2300ft, temperature corrected by ATC". When not vectored the clearance is "descend to 2000ft" and the pilot will report the altitude they will use according to their correction tables.
We have separate tables of altitudes what altitudes to use during vectoring in different temperatures.
If this is the case, during vectoring radar clears "descend to 2300ft, temperature corrected by ATC". When not vectored the clearance is "descend to 2000ft" and the pilot will report the altitude they will use according to their correction tables.
We have separate tables of altitudes what altitudes to use during vectoring in different temperatures.
Joined: Sep 2006
Posts: 2,181
Likes: 1
From: any town as retired.
Welcome Roger
Thank you for your post, and the video explanations.
As was mentioned on the comments after your presentation, the non precission is the problem, either hot and hi, or cold and lo.
Is the relationship to high pressure systems as found in Siberia, for example also similar to the temperature model.
In Siberia, the SLP can be 1045 perhaps, the temp -40c, easily. Do these balance out as ISA is no longer valid.
glf
As was mentioned on the comments after your presentation, the non precission is the problem, either hot and hi, or cold and lo.
Is the relationship to high pressure systems as found in Siberia, for example also similar to the temperature model.
In Siberia, the SLP can be 1045 perhaps, the temp -40c, easily. Do these balance out as ISA is no longer valid.
glf
