Far 91.144

[EnRoute]

"Temporary restriction on flight operations during abnormally high barometric pressure conditions"

Help me understand this as an aircraft performs better under higher pressure. This reg would be understandable if it were for "abnormally low barometric pressure"

What am I missing. I am sure it is blatantly obvious, but help me out here.
:banghead:anic:

 

[USMCmech]

The altimeters only adjust so far. Once you are past that limit, you are getting bad info from your pitot static instruments.

It's not really an issue in a Cessna, but Jets (especialy ones with FBW and FADEC) can really get confussed.

 

[casey]

some altimeters cannot be set to pressures that high.

This reg would be understandable if it were for "abnormally low barometric pressure"

no it wouldnt. If you go into the middle of the strongest hurricanes you might see a pressure as low as 900 mb (std surface pressure is 1013.25 mb). While this is a very strong low and you arent likely to see anything this strong, its only about 3000 ft as far as the airplane can tell. Performance is good reason for a high or low limit.

 

[EnRoute]

Is the reverse not true. What am I overlooking now???

 

[seagull]

Many altimeters are unable to be set above 31", so special procedures required. Unfortunately, these affect those of us that CAN set the higher settings also, as the need to have everyone on the same altimeter while being vectored around is higher than having a correct setting, so we set 31" on vectors, and the correct setting when we get on a published segment, essentially.