Monday, July 23, 2007

By the Numbers

I was just looking at some numbers for the Atlanta Hartsfield-Jackson (ATL) airport -- the world’s busiest.

From the Atlanta Journal-Constitution.

”1 million — The number of takeoffs and landings the airport will experience this year.

3,000 — The average number of daily takeoffs and landings at Hartsfield-Jackson.

218 — The record hourly number of takeoffs and landings the airport experienced on Wednesday from 7 to 8 p.m.

3,103 — The record number of daily takeoffs and landings Hartsfield-Jackson experienced in a single 24-hour period earlier this month.”

Then I went to Flight Aware and looked at the arrivals between 8 PM and 9 PM today (7-22-07.) There were 110 arrivals in that hour.

I then went to one of those FAA Traffic Management pages I found not long ago. VAPS stand for “visual approaches.” In essence, it means good weather in which the airport can operate at it’s most efficient. The best weather and the best runway configuration gives you an 88-96 airport arrival rate.

Those numbers don’t exactly jibe do they ? If your “best” rate is 96 an hour but you’re landing 110 an hour then something isn’t exactly right. I don’t see the fifth runway that recently opened at ATL listed so I guess that is it. But let’s look a little deeper while we’re here anyway.

Suppose the weather wasn’t good. That takes the arrival rate (even with the preferred runway configuration) down to 68 arrivals per hour. I’ll give you 32 extra arrivals on the “fifth” runway and make it an even 100 arrivals per hour in bad weather. (Quickly, ATL has 4 “main” runways. Two for arrivals and two for departures. The “fifth” runway was recently added.)

According to the AJC, the record was set between 7-8 PM. Half of 218 (arrivals and departures) is 109 arrivals. With a 100 an hour airport arrival rate you’ve got 9 arrivals left over. They get pushed into the 8-9 PM hour. But that hour has 110 scheduled. Add 9 and you’ve now got 119 -- or 19 more than can the airport can handle.

Imagine what happens if the airport arrival rate goes down to 55 per hour. It isn’t just weather you have to worry about. Imagine what happens to the airport arrival rate when an aircraft blows a tire and gets stuck on the runway. Or a hundred other little glitches.

You’ve got to ask yourself some questions. Is scheduling an airport at 100+ percent of capacity worth that super-duper deal you got on your last airline ticket ? Or would you rather leave a little “give” in the system to allow for an occasional glitch ? Is that “cheap” airline ticket worth a 2 hour delay ? 4 hours ? 9 hours ? You may not realize it but it really is your choice. It’s your National Airspace System. You paid for it.

Don Brown
July 23, 2007

No comments: