Thursday, March 05, 2009


Be it ever so humble (or not), it sure is nice to be home. It was a mostly uneventful trip. Beautifully clear leaving Vegas. Typically hazy arriving in Atlanta.

As I mentioned in the earlier post, the plane was a little late arriving in Vegas but -- as you so often hear the airline people say -- we were able to make some time up enroute. That announcement is so commonplace that people really don’t think about it. Except air traffic controllers.

Aircraft file flight plans to fly in the National Airspace System. All airlines are in the IFR (Instrument Flight Rules) system all the time (99.9% of the time anyway.) Included in that flight plan is a speed at which the aircraft will fly. Trust me, 99.9% of the time, the airline pilots never say they are changing that speed (even though they are required by regulation to do so.)

Now, you tell me -- do you really think they change their speed to make up time or do you think there’s enough cushion in their schedule that they’ll arrive “on time” anyway ? It’s hard to know what to believe isn’t it ?

The reason I’m mentioning it today is that you might remember this bit from yesterday.

Today we listened to the RNAV crowd trying to space arrivals into the hubs with CDA (Continuous Descent Approaches). That will require you to be at the same altitudes, on the exact same route and at the same speed as everyone else. And if they could do it, they’d adjust the speeds for hundreds of miles prior to the start of the CDA point.

(Why does it always fell strange, quoting myself ?)

In the above, I was referencing a presentation given by Dr. Jean-Paul Clarke of Georgia Tech about CDAs. Nice lecture. Nice guy. It was all interesting although I’d really heard it all before. The gist of the problem is that somebody has to put all the airplanes in line because landing on a runway is no different than going through the checkout line at the grocery store -- you have to get in line. We can let the Approach Controls put them in line or -- if you want to use a CDA to save fuel -- you can let the Centers put them in line while they’re still up high. Actually, we’ve always done a little of both. But that’s another story.

Dr. Clarke commented that he found that, sometimes, pilots don’t cruise at the optimal speed for their aircraft. Shocking to controllers and pilots -- I know (wink, wink.) That was about the time he mentioned he would like to use speed adjustments hundreds of miles prior to the start of the CDA point. Sounds good. Until you run across that pilot that is trying to make up lost time. Or turbulence makes you slow down. Or the company calls the Captain and says to pick it up, they’ve got 40 people that will miss their international connections if they don’t get in by 5 PM.

This is the problem. Dr. Clarke has come up with the formulas to handle the unbelievable number of variables he’s been given. Seriously, he only included one equation in his presentation and it made the audience cry it looked so painful. (I did tell him there was a certain math whiz at GaTech that might find it interesting.) Being the proverbial rocket scientist, he was probably the smartest person in the room. But, he’s not a controller. Neither are the airline executives asking for the policy nor the FAA managers that are trying to implement it. Maybe the FAA should hire a historian.

We’ve been here and done this. I’ve had a half dozen controllers already write me and ask if I remember the “Keep ‘em high” program. The overwhelming concern that drove that program was noise abatement.

” Another operational rule under consideration involves possible restrictions on minimum altitudes in terminal areas by keeping airplanes high. Such restrictions would reduce the noise impact on the ground by maximizing the distance between the airplane and persons on the ground. This has been the FAA "Keep 'Em High" Program. A proposal on this subject to convert it from an air traffic management program to a regulatory requirement was submitted to the FAA by the EPA and was published in the Federal Register on January 6, 1975, as NPRM 75-40. “

Trust me. When some other entity in the aviation world figures out that CDAs are goring their ox, we’ll change them too. We’ll probably go back to something else we’ve already tried before. And it will all be because it will save time and gas--I mean greenhouse gas pollution--I mean noise pollution. (Did someone mention Newt ?) Oh, you know what I mean.

Don Brown
March 5, 2009

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