On Tuesday, September 26, 2017 at 2:06:33 PM UTC-7, John Cochrane wrote:
It will be interesting to hear more details. This happened over Beloit Wisconsin, where there is a glider operation, so it was likely a Beloit-based glider.

Other Chicago operations -- Chicago Glider, Sky Soaring, and Hinckley -- are much closer to O'hare class A. When I flew out of each, attention to this issue was intense. Sky soaring especially operates frequently on the edge of class B, so we watched for traffic coming out our going in the side of class B. Transponders are very common in these close-in operations. Chicago glider club flies near the common southwest approach over the Joliet VFR, near the edge of MDW class C, and transponders are pretty much universal. Flying there we often saw 737s take gentle turns to avoid a thermal, alerted to us via Transponders.

Reports from Chicago say it was an excellent day for soaring with much higher altitudes than usual, around 7,000'. Still, what was a O'hare bound jet doing that low, in class E airspace, that far out? Airline pilots, is this a common route and practice? It would seem that staying above 10,000' until quite near the massive Ohare Class B would be prudent!

Chicago airspace is full of light aircraft. Gliders are a small part of the traffic. It always puzzled me flying from Chicago Glider, and puzzles me now as a Southwest passenger, just why the approach to Midway lets down to highly congested class E airspace under 10,000' way outside of the Class B or C and then motors on through swatting the proverbial bugs off the wingtips as they come in. It's nice for me to review all my old landing sites from close up, but I don't think that's what they had in mind.

John Cochrane

Flight originated at Sky Soaring (as marked on the SeeYou database).

I put the two flight traces together in Google Earth. Here's a link to some imagery.

https://drive.google.com/open?id=0Bw...E4wTkxheHU4bFU

Looks like the two aircraft first started evasive maneuvers at around 19:44:24 UTC with the 737 at the ASH-26E's 10 o'clock or so and no more than a few dozen feet difference in reported altitude. The glider dove off a 150 feet or so to the north and the 737 climbed a similar amount and passed each other with maybe 500' horizontally 8-10 seconds later. Without the evasive maneuvers it looks to me like a coin flip whether the two would have hit each other - the 737 went right through the middle of the thermal and the altitudes were within measurement error. Obviously the pilots will have a lot more to say about that.

I'd repeat what Darryl said about transponders and knowing arrival/departure routes.

Andy