Thursday, December 13, 2007

Close But No Cigar



I wonder how much your average reporter -- much less your average citizen -- can follow along as we watch the National Airspace System implode. For instance, do you think anybody caught this one ? On 12/7/07, Matthew Wald of The New York Times reported on the Port Authority of New York and New Jersey’s (PANY/NJ) recommendations to ease air traffic congestion in the New York metropolitan area. In his story Mr. Wald had this:

“Others would entail actions -- like using three runways simultaneously instead of two at Kennedy -- that controllers have in some cases deemed unsafe.”

Before I fast-forward to 12/11/07, let me say this. I downloaded the PANY/NJ report and read it. It’s 99.99% pure fluff. However, Mr. Wald picked out an interesting example -- on Friday, the 7th. Let’s fast forward to Tuesday, the 11th.

Commuter Jet and Boeing 747 in Near Miss

"A 37-seat commuter jet arriving at Kennedy Airport nearly collided with a Boeing 747 cargo jet on Sunday afternoon when the Boeing, which was supposed to land on a perpendicular runway, failed to do so and continued across the smaller jet’s path, controllers at the airport’s tower said yesterday.

Controllers were using the perpendicular runways to keep up with the stream of arrivals. The runways are separated by a few feet of grass, but the flight path from one leads directly across the other."


Give that man a cigar. They were close.

What you probably didn’t read was this:

US Airways flight, small jet nearly collide in midair

”A US Airways flight bound for Charlotte and a small private jet leaving Statesville narrowly missed hitting each other Tuesday morning about 15 miles west of Greensboro, a representative of the air traffic controllers union said.”

”When the small jet's pilot said he couldn't climb that high, the controller tried to direct Flight 829 to hold its altitude, Phillips said. But the US Airways pilot didn't respond for several seconds, Phillips said, and the two planes ended up at about 16,500 feet and about eight-tenths of a mile apart.”

In that I used to work that airspace and I can still clearly picture all this in my head, let me read between the lines for you. The controller was working on a “swap.” He was trying to get the private jet above the USAir. The USAir was inbound to Charlotte (CLT) and descending. If the timing is right -- and the aircraft are descending and climbing quickly enough -- the airplanes will “swap” altitudes before they ever get within five miles of each other. But if they don’t, you’re left with nothing. Evidently, it wasn’t going to work and the controller tried to level them off at different altitudes-- a thousand feet apart. But aircraft can’t stop a steep climb or descent immediately and it didn’t work.

Here’s the scary part -- “eight-tenths of a mile apart.” That sounds like a lot of distance to non-controllers. It might even sound like a lot of distance to an Approach controller. But for a Center controller -- people that work on radar scopes set at 60-125 mile ranges -- “eight-tenths of a mile” means that the radar targets merged. On the ranges typically used in the Centers, the radar targets are about a mile wide. From this controller’s perspective, these two airplanes merged.

Now stick with me here, we’re going to go someplace you weren’t expecting. Remember all this talk about NextGen and how GPS and ADS-B are more precise than radar which will allow controllers to run airplanes closer together ? Let me ask you a question. How large will an ADS-B target be on a Center controller’s radar scope ? Will it still be a mile wide ? I assume we could make it one pixel wide but we want controllers to be able to see it. All you pilot types that read this blog -- how wide are the aircraft symbols on your traffic display (TCAS or TCAD) ?

If you haven’t thought of this angle, you probably don’t need to be giving advice on how close controllers can run airplanes. Just a thought for the folks at the Port Authority.

Don Brown
December 13, 2007

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