Does ADS-R show non-transponder aircraft?

Discussion in 'Flight Following' started by flyingcheesehead, Jul 12, 2018.

  1. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    I was thinking about this tonight. I'm hoping our resident ADS-B guru @John Collins will pipe up here.

    ADS-R (Rebroadcast) is a service that sends ADS-B Out equipped aircraft the radar positions of non-ADS-B equipped aircraft in their vicinity (+/- 3500 feet and 15 miles, IIRC).

    I'm wondering - If an aircraft has its transponder turned off and thus no altitude readout, does ADS-R still send its position to equipped aircraft?
     
  2. Axtel4

    Axtel4 Pre-takeoff checklist

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    The short answer is, no. ADS-R is a rebroadcast of an ADS-B signal on the other band. For example, it is the rebroadcast of a 1090 ADS-B signal on the 978 UAT band. If the intruding aircraft is equipped with ADS-B Out, and the transponder is off there would be no ADS-B signal to be rebroadcast.

    TIS-B on the other hand is the ground station broadcast of a Mode C equipped aircraft on the 978 UAT and / or the 1090ES band. The position (bearing) of a TIS-B report of the Mode C aircraft is derived from the ATC RADAR position data and the altitude of the TIS-B report is derived from the Mode C reply of the intruder aircraft. TIS-B will only report the position of transponder equipped intruder aircraft. If the intruder does not have a transponder, or the transponder is off, the aircraft will not be reported on TIS-B.
     
  3. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    Thank you.

    So, for all those of you going to Oshkosh, that means that non-ADS-B equipped aircraft, which should be turning their transponders off, will not show up on your magic boxes. Dangit.
     
  4. SoCal RV Flyer

    SoCal RV Flyer Pattern Altitude

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    NOTAM sez set 'em to Standby at or before Ripon.
     
  5. DaleB

    DaleB En-Route

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    Yep. The last two years I flew up with my Stratux and tablet running Avare. Traffic display got pretty dense as I was approaching Ripon, then almost disappeared. There were still a few who didn't turn their transponders off, but for the most part they all disappear. I remember it, but I don't remember all the details... once I left Portage I got a little too busy staring out the canopy to be staring at the tablet.
     
  6. PaulMillner

    PaulMillner Pre-takeoff checklist

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    Not only does it ignore non transponder aircraft, it ignores transponder aircraft without Mode C.

    Paul
     
  7. TigerGene

    TigerGene Pre-takeoff checklist

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    If you are ADS-B equipped, turning the transponder to standby may not affect your ADS-B out transmissions, you are likely still transmitting.
     
  8. aggie06

    aggie06 Pre-takeoff checklist

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    I thought the notam said for only non ads-b equipped aircraft to turn transponders off. I better check that again. I have TCAS in my airplane, so I can see all the transponders on along the tracks toward the airport. Seemed like most were still on last year. Except that guy in the Mooney who cut me off after Fisk.
     
  9. flyingcheesehead

    flyingcheesehead Touchdown! Greaser!

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    30 miles out from OSH, actually. So, well before Ripon. Which kinda sucks, if we can't see 'em on our magic boxes.

    And yes, only non-ADS-B ones are supposed to be turned off. ADS-B, you keep them on.

    Frankly, at this point, I think they should just have everyone keep them on. There was some reason having to do with radar getting saturated by mode-C replies that they had everyone turning them off before... But doesn't mode-S have a Mode-C response as well? If that's the case, I would think that we're probably going to be saturating it anyway, so we might as well have everyone on. Even if mode S doesn't have a Mode C response as well, I would think then that we've reduced the Mode C traffic to the point where they can leave them on.
     
  10. SoCal RV Flyer

    SoCal RV Flyer Pattern Altitude

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    Actually, it says make sure lights are on 30 miles out. Xponder to standby at or before Ripon for non-ADS-B aircraft.