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Wondering what specifically the issues are. Obviously, taking off and landing have more 'moving parts' but more curious about the actual extreme cold.

I assume the operating temperatures at cruise are much lower than ground temps.

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  • $\begingroup$ For landing, the altimeters are affected at very low temperatures. The altimeter will indicate a higher altitude than actual. $\endgroup$ – Mike Brass Jul 17 '18 at 19:28
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The extreme cold is not an issue so much as the weather that typically accompanies it and the fact that planes are not always designed to be started in extreme cold with out some assistance even if they can run in it. For example so long as the weather is good and the aircraft are equipped, there are plenty of airports in Antarctica

When extreme cold is accompanied by precipitation you can get ice build up on the runway which is quite dangerous. Most airports that are in an area of regular cold weather are equipped in some way to handle this.

Extreme cold temperature that comes with/because of frontal movement may also come with very high winds that can exceed aircraft limits. But high winds can come with warm weather as well so this is not exclusive to the cold.

For piston engines you have an issue of thick oil. When the temperature drops the oil thickens and it becomes hard to start the engine as well as running the risk of engine damage. Piston engines in commercial operations are much less common than they once were so this is less of an issue. However the general aviation fleet is still pretty effected by this issue.

Jet engines do have cold start procedures just like piston engines, there is a good discussion on that here. You can see a neat video of an A320 starting up in -28C conditions here so cold weather starts are not a huge issue.

Most airports have some form of ground crew that operate in the elements. Crew like baggage handlers, aircraft marshaller, and even mechanics may work out on the ramp to get an aircraft loaded and ready to go. This is one instance where sheer cold can be a factor although weather can also make working conditions very tough, even if proper protective gear is available.

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At cruise levels, the air holds nearly no water vapor and therefore the problems of icing & snow are less likely to occur than on ground.

Also, with already running engines, there is heat available to keep even with low outside temperature parts of the aircraft heated, e.g. the wing edges as anti-ice measures. I don't know the details about jet engines enough, but it might be, that they have a narrower temperature range for startup than for cruise settings. So it might be okay to run an engine at -20°C but not to start it at this temperature - but that's something hopefully others will know better and write a more detailed answer about that.

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On the design side, transport aircraft are certified for a minimum operating temperature, typically -40C, sometimes -45 or maybe -50, and this will be a basic operating limitation, but only for departure purposes as it will regularly see -70 at high altitudes in the winter in the north.

This means that an airplane certified to -40 will not be able to legally depart an airport with an SAT of -45 and will have to wait around for the temperature to warm up. This happens in the arctic quite a bit.

Operating components are also certified to the airplane's minimum temperature limitation and will have to perform to the required standard in endurance and qualification testing only to that minimum temperature, not the temperature it might be exposed to at altitude. This can cause problems for mechanical non-hydraulic components away from the fuselage, like screwjack flap actuators(hydraulic components get warmed by the fluid and never really get cold soaked). In theory, if you tried to deploy flaps at 35000 ft at -65, chances are they won't come out because the grease or oil in the gearbox is congealing.

However, this isn't the problem it seems because when the flaps are called for, the airplane is back down to somewhere around 3000 ft agl and components have warmed up at least to their min cert temp and can be expected to work.

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