EAA493 Mailing List: Re: Couple of ADS-B events

[Don Smucker (dws_jmc]

Hmmm. Thinking about this a bit more, I may have misspoken.  My post above is how the system operates as described to me by an Oshkosh vendor.  However, since the 978 traffic broadcast, which is definitely triggered and sent only when an ADS-B tower received a "broadcast request". ie, a ping, from either an ADS-B transmitter ("out" from an airplane), or a transponder reply sent from a transponder with "extended squitter"), is not specifically sent to a specific airplane, it is broadcast from the tower to all who can receive the signal.  So the traffic must be all the traffic the system knows about (any transponder, plus transponders with extended squitter plus any aircraft with ADS-B out), within a certain radius of the transmitting tower, centered on the tower.

Can anyone definitely answer this question?  I would need to do some additional research to be sure, but I don't see how the traffic picture could be just centered on the transmitting/pinging aircraft when there may well be multiple aircraft in the tower's area sending signals - shifting traffic would be confusing to everyone.  But, that is how it was explained to me.

Don S.

On Thursday, August 14, 2014 5:42 PM, Don Smucker via EAA493 <eaa493 [at] fly-web.us> wrote:

I bet the balloon was tethered.  There used to be a tethered one in southern NM.

As for ADS-B traffic, if you have a transponder on, then you show up on ADS-B traffic.  The ADS-B traffic picture shows everyone who is painted by ATC (ie, has a transponder turned on) as well as all traffic with ADS-B out.  So I agree with Gerry's analysis - you were most likely seeing your own airplane, based on transponder activity.  Keep in mind also that ADS-B traffic pictures are based on pings (for want of a better word), with the "pinger", ie the plane with ADS-B out that caused the system to send out the traffic picture, shown in the dead center of the traffic broadcast.  In other words, the system does NOT send OUT the ADS-B traffic picture (on 978) unless and until an airplane somewhere in your area WITH ADS-B OUT or with an extended squitter transponder, pings the tower.  Thus, you will not receive ADS-B traffic pictures if no plane with ADS-B out (or extended squitter transponder) "pings" the tower near you.  And, to repeat, the picture that will be sent out when a plane DOES cause an ADS-B traffic broadcast, will be centered around the airplane that "pinged" the tower.  Also, I believe (but have not verified) that weather sent out on ADS-B from ground facilities does not require a "ping - that it is always sent out on a short interval basis.  But I could be wrong on this point.  In any case, that is why an ADS-B receiver is a pretty good thing to have, in that you get weather cheaply (free, except for the receiver purchase cost, which is quite modest), plus you get free traffic signals from time to time (but only when someone else in your area "pings" your local tower, and recognizing that the resulting traffic signal is centered on the "pinging" aircraft), BUT you get so much more if you have either ADS-B out as well, or a transponder with extended squitter.

Finally, just to clarify, EITHER a certified ADS-B out unit OR a transponder with extended squitter, is required by 2020, and either meets the requirements.

Hope that helps.

Don S.

On Thursday, August 14, 2014 5:11 PM, Joe Christian <k5hmd [at] uppercanyon.us> wrote:

Don’t guess I see how the other aircraft could see me since I don’t have ADS-B out, and I was level at 8500, while he was showing 8125.  I also thought that you could “see” other aircraft if you were close enough to receive their ADS-B out signal.  I’ve just started researching ADS-B technology, so still a novice!

 

My first thought was a balloon at Roswell, but would have thought the wind up there would be more than 1 knot.

 

From: EAA493 [mailto:eaa493-bounces+k5hmd=uppercanyon.us [at] fly-web.us] On Behalf Of Gerald Hatch via EAA493
Sent: Thursday, August 14, 2014 4:42 PM
To: Joe Christian
Subject: Re: [EAA493] Couple of ADS-B events

 

This may answer one of them, the shadowing.

 

Since you do not have ADS-B Out, the traffic picture is the result of another aircraft "pinging" (not really pinging but just requesting) traffic info relative to his position and he would be seeing you. The difference in position maybe the delay in the system. The 60K ft and 1 knot thing, I have no idea other than a balloon.

Gerry 

PS. All of the traffic you saw on the screen was the result of another airplane with ADS-B out getting the info relative to his area of coverage which in those cases included you.

 

On Thursday, August 14, 2014 4:34 PM, Joe Christian <k5hmd [at] uppercanyon.us> wrote:

 

Judy and were flying to Ruidoso on Tuesday and I started receiving ADS-B traffic information on several aircraft in the Midland vicinity.

 

At any rate, when I was northwest of Midland, I noticed I was being closely shadowed.  The other plane was close behind me, and about 400’ lower.  I would guess a Customs pilot was getting some practice.

 

The other event is not easily explained.  As I got close to Roswell, I noticed a “airplane” right over the ADS-B tower.  It was at an altitude of 60,025 feet and had a groundspeed of 1 knot.   Don’t have a clue what this one was???  Anyone venture a guess?

 

Joe

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