Oooooooh, I’m Scared

I was on the internet doing some research (I don’t pull this stuff out of thin air you know) and I got this message from an FAA web site.

”You have attempted to access a RESTRICTED area of the Command Center website. Your intrusion has been logged and it will be investigated by our webserver administrators.”

Ooooooh, from the “Command Center” too. Get a life Buzz Lightyear. Spend some time making your website workable instead of trying to scare people.

Reporters, pay attention. I was looking for data on CLT (Charlotte, NC) and ATL (Atlanta, GA) but I’ll have to settle for PHX (Phoenix, AZ). I already know all this stuff but I guess you have to be able to prove it to people.

PHX Traffic Management Tips

“This results In an arrival rate of 48-52 during IFR weather conditions.”

Okay. So, PHX has an “arrival rate” of 48-52 airplanes per hour during Instrument Flight Rule conditions or what civilians would call “bad weather.”

Now you go to FlightAware. If you click on “Analysis” it conveniently pulls up PHX but let’s go to all the statistics on PHX.

If you’ll look at the first chart you’ll see that PHX has right at 60 arrivals scheduled at 1300. That’s 1 o’clock in the afternoon local time (unless they’re using GMT and the point is really moot regardless.)

The FAA Command Center’s web page on PHX has a VFR arrival rate of 76 on a West Operation. VFR is “Visual Flight Rules” or “good weather.”

Let’s start adding it up.

Good weather -- PHX can take 76 an hour.
Bad weather -- PHX can only take 48 per hour.

The airlines that sell tickets for PHX sell tickets for around 60 airplanes an hour. And they’ll sell you a ticket 90 days in advance. A 5 day weather forecast isn’t worth much. They have no idea what the weather will be like in 90 days.

On “good weather” days things work okay. Not always great (more on that in a minute) but okay. On “bad weather” days, they don’t work well at all. At a minimum, 8-12 airplanes will take some kind of delay (somewhere) around 1300. What kind of delay will depend on who’s doing the talking. If it’s your friendly airline gate agent it’ll probably be an “ATC delay” because that is what they’re told to say. Here’s a hint: People don’t understand ATC so they’ll accept that explanation. Besides, it sounds better than, “Our CEOs can’t count.”

PHX isn’t known for “bad weather.” But ATL is. And CLT. And EWR (Newark, NJ), LGA (La Guardia, NY), JFK (Kennedy, NY) and ORD (Chicago, IL). You can check them out if you like but you’ll see the same problem. As to why it doesn’t work any better in “good weather”...

If you’ll click on the button at FlightAware that says “View Airport Activity” and then “More” on the next page, you’ll get to this page. And on it you’ll note things like COA169 and SWA2471 are scheduled to arrive at exactly the same time -- 5:45PM MST. I assure you, both airplanes will not land in formation on the same runway.

The real lesson comes when you take the time to do the math. Look at just about any 15 minute window and you’ll discover that more arrivals are scheduled than can land in that period of time. In that I hate math, I’ll just refer you to where I took the time to do it before.

”To put it in real-world terms: At Charlotte, N.C., the very best airport acceptance rate you can expect is around 70 airplanes per hour, or about one plane every 51 seconds. That is if the wind doesn't blow the wrong way, the weather is good and all the planets and stars are aligned correctly. This explains why the airlines schedule 78 per hour -- because we all know how reliable perfect weather is. Actually, the airlines don't schedule 78 per hour; they just schedule a bunch of planes to arrive in a short time span. But to get all those flights on the ground during that time span, Charlotte would have to land a plane every 46 seconds and Charlotte can't do that even on the best day. Someone is going to be late; and lots of flights will be late when the wind shifts and the storms move through.”

In other words, it isn’t the number of airplanes per hour that will give you the whole story. It’s a convenient figure to use -- even I use it. But in order to understand why there are delays -- even on perfect days -- you need to look at the number of arrivals (and departures) per minute.

You thought I forgot about the departures didn’t you ?

Once you soak all this in, read this article and see if you can believe a word the ATA is saying.

Don Brown
July 3, 2007