cold weather IFR altitudes

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jlfd26
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cold weather IFR altitudes

Post by jlfd26 » Wed Feb 20, 2013 6:57 am

I was studying once again my CAP-GEN and something caugt my attention. In the mountainous regions page there is a paragraph where it is written:
in winter when air temperatures may be much lower than those of the international strandard atmosphere (ISA), aircraft should be aperated at an altitude which is at leat 1000 feet higher than the published MEA/MOCA
I was wondering what is much lower for you guys? -10?-30?

Thanks for the answers
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ahramin
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Re: cold weather IFR altitudes

Post by ahramin » Wed Feb 20, 2013 11:09 am

When the temperature is low enough to affect your altitude by 20% of the terrain clearance. In mountainous areas this would be 300-400 feet.
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pdw
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Re: cold weather IFR altitudes

Post by pdw » Wed Feb 20, 2013 4:03 pm

OK, the 20% correction is at around -30C ... but doesn't that become a much larger correction (ie 2000' higher than MEA) needed if that's 10K above the station in mountains ?
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SplitS
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Re: cold weather IFR altitudes

Post by SplitS » Wed Feb 20, 2013 4:20 pm

Do what keeps you safe. Keep it simple - dont fly at the MEA/MOCA, fly higher. Correct your altitudes when 0 or below. Simple no?
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bezerker
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Re: cold weather IFR altitudes

Post by bezerker » Wed Feb 20, 2013 6:32 pm

Just do the corrections and you will be fine.

-30° is approximately where the correction is 20%

25 mile safe altitude and other non-mountainous areas only give 1'000' clearance.

So, at a 5,000' 25 mile safe at -35° you may hit terrain (25% of 5,000 is 1,000).

In a mountainous area there may be a 10,000' safe altitude, in which case you may be 2,000' lower than anticipated at -30°.
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ski_bum
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Re: cold weather IFR altitudes

Post by ski_bum » Sat Feb 23, 2013 6:51 am

The is an excellent app for the iPhone/iPad called cold altitude, I believe it was designed by an Air Canada pilot... Works awesome and use it all the time in the arctic.
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ahramin
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Re: cold weather IFR altitudes

Post by ahramin » Sun Feb 24, 2013 2:33 pm

-30 is where the correction hits 20% at 200 feet difference between altitude and alimeter setting source. It is NOT where the correction hits 20% for everything. I hear this a lot from a lot of airline types lately who have failed to read and understand what the 20 is a percentage of.

As said, MEAs have terrain clearance of 1000 to 2000 feet. It doesn't take -30 degrees to get an error of 200 feet at 5000 feet.
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jlfd26
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Re: cold weather IFR altitudes

Post by jlfd26 » Tue Feb 26, 2013 12:46 pm

thanks for the answers

is there an equivalent app in the android market because I got rid of my iphone and wanted change
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SkyWriterSoft
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Re: cold weather IFR altitudes

Post by SkyWriterSoft » Thu Feb 28, 2013 10:39 am

FlyBy E6B does cold wx corrections as well. There is a free trial version on the Google Play store for Android.
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