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Glider near miss with Airliner (emergency climb) near Chicago yesterday?

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Old Today, 12:38 AM posted to rec.aviation.soaring
Darryl Ramm
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Default Glider near miss with Airliner (emergency climb) near Chicago yesterday?

On Monday, October 16, 2017 at 11:01:03 AM UTC-7, Dave Nadler wrote:
On Monday, October 16, 2017 at 12:57:35 PM UTC-4, Ramy wrote:
This is disturbing news to hear that the military can not afford to
comply with the ADS-B requirement while GA is required.
And why the wingmen in formation turn off their transponders?

Hi Ramy - IIRC, for civilian formation flying, procedure is normally
the same; only one in formation has transponder on. Why?
Because otherwise they all get interrogated at the same time,
they all answer at the same time, and the result is unintelligible
(this is called "fruiting", kinda like everyone shouting at the
same time - even worse than RAS).

In principal this is less of a problem with Mode S, except a
mode S transponder behaves like an old Mode C when it gets an
old-style interrogation. And while ground stations send new-style
interrogation, older TCAS-I installations send the old-style
interrogation. And these are installed in better-equipped GA
aircraft like Lee's Bonanza.

Darryl, please correct if I've garbled (fruited) this...

Hope that's clear!
Best Regards, Dave

Yes that's right and with Mode S transponders primarily being interrogated by Mode S capable SSR you can likely leave multiple transponders on in a formation flight. I have no idea if the military ha moved to do that more recently or not. The selective interrogation of Mode S deals with what would otherwise be fruiting/overlap of the Mode A/C replies. Even with Mode C transponders I've had comments from controllers and radar techs that modern radar systems are able to deccorealate several closely based Mode C targets. I've got no hard numbers on that.

Transponder use patterns is another thing to ask about when talking to ATC or airforce MACA reps etc.

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