"Maybe, or maybe FL180 is a nice clean line for class A airspace. No need to bother transcontinental flights for a local issue."
Way more plauible
"Maybe, or maybe FL180 is a nice clean line for class A airspace. No need to bother transcontinental flights for a local issue."
Way more plauible
FL180 is the floor of Class A airspace, "the flight levels", where airliners etc. operate.
Relevant chapter from FAA "Pilot's Handbook of Aeronautical Knowledge": https://www.faa.gov/sites/faa.gov/files/17_phak_ch15.pdf
In the "Flight Levels", altitudes are referred to not in feet above sea level but as "FLxxx" where xxx is a nominal altitude in 100s of feet.
Altimetry is done using barometric pressure. Since this varies with weather, airplanes at lower altitudes set their altimeters to the local barometric pressure for a reasonably accurate reading. In the flight levels, where planes are typically covering ground quickly and there is very little chance of your path conflicting with the surface of the Earth, every plane sets to an agreed-upon reference of 29.92 inches of mercury as the altimeter setting.
What does that mean sorry?
It means any aircraft transitioning over the area at high altitude isn't impacted, because they're too high to care.
It is a ground and "everything near the ground" stop. Meaning low altitude helicopters and private aircraft have to consider it, even transitioning, but realistically commercial aircraft not taking off/landing in the area won't.
FL180 is 18000 feet, meaning that flights OVER don’t need to divert.
It is a pedantic but meaningful distinction that I'd only point out on a sorta geeky site like this, but actually, FL180 (or, flight level one-eight-zero) is the altitude at which an altimeter will read 18,000 feet if it's set to assume that the barometric pressure is 1013 hPa (29.92 inHg). Above a certain transition altitude, aircraft switch their altimeters from reading altitude in the local pressure to this "standard" pressure. This is because above that altitude and safely away from terrain, it's no longer important to know precisely how high you are, but it _is_ important to know what altitude you are relative to all the other aircraft nearby.
It means that you have no business being below FL180 or 18,000ft to enter this airspace.
That it limits local flights but not international ones as they fly higher.