FAR 91.144 talks about restricting flight operations during abnormally high barometric pressure conditions. Why would there not be an identical restriction during abnormally low barometric pressure conditions?

This seems to be the more dangerous situation. In the "abnormally high" situation, if the altimeter can only be set to 31.00 and below, then it will tell you you are lower than you are, which gives a safe bit of padding. In the "abnormally low" situation, if the altimeter setting drops below 28.00 and the altimeter can't be set any lower, then the pilot has no padding and is actually lower to sea level than the altimeter says he is.


1 Answer 1


Typical low pressure goes down to around 29.20 while typical high pressure is around 30.60. This means that the pressure is more likely to exceed 31.00 than to be lower than 28.00.

The weather is also a factor. Higher pressure is generally associated with good weather for flying, while extreme low pressure is associated with major storm systems where you wouldn't want to be flying anyway. Even many major storms don't drop below 28.00 at their lowest point. Just looking at the cyclones so far this year, anything below 28.00 (948 hPa) has winds peaking over 100 mph.


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