Close call over Denver 11/23

Sources: Passenger Jets Were 200 Vertical Feet Apart

CALL7 Investigation: Planes Nearly Collide Over Colorado



I’ll have a map with their respective tracks plotted in about an hour.

If I did this right, here’s the permalink to the Republic flight. … /KOMA/KDEN

You do see some interesting movement around the Sayge point on the sectional…

Done Right.

…and about a minute later than NeedleNose! :smiley:

If Fergus is right, then this is definitely a deal. Loss of vertical and horizontal separation. The crossing restriction at SAYGE would still be in Class A airspace, so the horizontal separation was lost by 1000ft. The question that needs to be asked is if RPA1539 was asked to descend any further on his arrival to KDEN. Assuming that he already passed SAYGE, altitude/speed would need to be coordinated with D50. If he went back to SAYGE and was still under ZDV control, he would have to be at least at FL190, putting them head on with the SKW arrival.

The TRACON is in the clear on this, so it definitely is 2 deals, possibly 3, for the ZDV controller:

  • Loss of horizontal separation between RPA and SKW.

  • Loss of vertical separation between RPA and SKW.

  • Loss of vertical separation between RPA and FFT.


  • Positions based on data in the FlightAware tracklog for respective planes.
  • Blue dots are Republic Plane
  • Green dots are SkyWest Plane
  • The number in the waypoint name is the time (MDT) for that plotted position. Example: “REP-647” is the Republic plane’s position at 6:47 AM.

For bonus points, how does TCAS decide which airplane climbs, and which one descends?

leeward has rights over windward when on same tack, oh wait, wrong hobby

Think you could add in FFT615 with this? I can see where the loss of vertical and horizontal separation would happen between RPA and SKW, but I’m not sure if it would be horizontal or vertical between RPA and FFT. The article doesn’t mention which one climbed and which one descended. Assuming RPA climbed, The only way FFT would have lost horizontal separation would be if it were very close in trail of SKW (leading it to have loss of separation between FFT and SKW and RPA. Subsequently, that would put RPA at WAFDOF, with the next usable altitude being FL210). Vertical separation wouldn’t be the problem there.

So if FFT lost separation, that would mean that RPA had to have descended for the TCAS alert, and descended to where they were less than 500ft below FFT, and still opposite direction.




We don’t have TCAS and it’s been 2 years since I had RVSM class and they explained it. So tell us how.

As arbitrary as it sounds, the airplane with the higher serial number traffic processor is the “master” airplane, and it is ordered to climb for the resolution. Vice versa for the other aircraft. It apparently took years of bickering between ICAO countries to finally come to that solution.

I can probably add it and post it in the early afternoon Friday.

Understanding this is investigated as controller error. It looks like the Republic plane was 5 nm off course at SAYGE. If they were more on course, their turn wouldn’t have caused an issue. I think the pilot would’ve been prudent to mention to the controller that they had already passed SAYGE, and THEN query the controller about returning to the fix.

They didn’t tell us that in RVSM class at Simuflite but they did describe how everything else works.
I’ll remember that to stump the next guy 8)

This reminds me of something I’ve been wondering and meaning to bring up - I know this is a big deal with commercial aircraft, but how often does stuff like this happen at small uncontrolled airports with ga traffic? A couple of weeks ago, we were tailgating before the FSU/Clemson game in a lot right near Clemson’s airport (KCEU). It was a little after dusk and kind of hard to see, but I watched a single engine something on approach and a small biz jet come from behind on the se. The single engine approached straight in and the jet made a 90 degree left turn and got in right behind the plane. I figured the whole time I was watching that the jet saw the plane, but he closed to about 200-250 yds (as it looked to me and I was really close) before he finally banked pretty sharp to the right and went around. By that point, I had my girlfriend and a buddy looking up too - I didn’t know what I was about to see. On one hand, it seemed like I was watching something that never happens, but then again, who really knows?

That’s kind of what the story said in OP’s link, unless I missed something.

Were they facing head on?

From the story:

Republic Flight No. 1539 was vectored on a route toward DIA that was south of the Sayge “highway” and running parallel to other air traffic.

So the pilots were not really off course as they were apparently following instructions.

The video in the story makes it sound that way, but they crossed paths nearly perpendicularly.