91.144 Question?

[JB74]

§ 91.144 Temporary restriction on flight operations during abnormally high barometric pressure conditions.

(a) Special flight restrictions. When any information indicates that barometric pressure on the route of flight currently exceeds or will exceed 31 inches of mercury, no person may operate an aircraft or initiate a flight contrary to the requirements established by the Administrator and published in a Notice to Airmen issued under this section.


Is this reg in place because most altimeters are mechanically limited to 31.00 hg, or is there more to it?

Thanks

 

[Mmmmmm Burritos]

Yes, that's pretty much why. If the actual altimeter setting is 31.30" and you can only set 31.00" in your altimeter, you will actually be flying 300 feet higher than you indicate. That will be fine for terrain clearance because you are higher than you think. The reg doesnt prohibit flight when above 31", it just says you must do what the issued NOTAM says.

AIM 7-2-4 and 7-2-5 go over this a bit, but AIM 7-2-2 is the big one to read.