On an average day, how many airplanes are in the sky across the United States?

Hey Matt:

With dozens of flights continually taking off and landing and airlines bragging that they're adding more flights, it amazes me that they don't run into one another more often...or that we don't look up and see a mass of airplanes. On an average day, how many airplanes are in the sky across the United States? What's the peak time and quantity?

-- Jeanne, the net

You and Chicken Little can stop worrying about the sky falling. The air above is divided into patterns a little like freeway lanes, and at any given moment, when a commercial plane is at cruising altitude, it has plenty of wing space all around. The real problem is that planes have to take off and land from a limited number of precise locations. Like trying to empty Hoover Dam through a few dozen funnels. So it's no surprise that the place you're most likely to be hit by another plane is on the ground. That's where most planes are at any particular time. Airlines can schedule all the flights they like. They can advertise the new Five-Martini Special to Vegas leaving Lindbergh at 6 p.m. every Friday night. They'll have the plane ready, you'll get on at 6 -- so far no lies -- but if you actually get into the air by 7:30, consider yourself lucky.

For the sake of air safety, there are just so many planes that can take off and land in any given amount of time. Planes in the landing pattern, for instance, have to maintain a certain distance from the plane ahead because of air turbulence and the time it takes to get that plane off the runway after it lands. For the brief time you're actually in the air, life is relatively peaceful.

The FAA claims it's impossible to give any kind of realistic estimate of the number of planes in the sky at one time. They do say there are 23,000 scheduled takeoffs and landings in the U.S. daily (610 of those are at Lindbergh; even more at Palomar and Montgomery). That's not 23,000 individual planes, of course; in a day the number is probably closer to a quarter of that. A single plane can take off and land many times in the course of 24 hours. So at 12:08 p.m. on a Tuesday, who knows how much metal is in the sky? Anyway, a real total of airborne things would have to include business jets, recreational (general aviation) flights, helicopters, blimps, and military operations. Too many imponderables for the FAA to deal with. They're still trying to figure out how to get us off the ground on time. And when's the peak time for us to be left sitting on the runway? Thursday and Friday evenings between 6 and 9.