Transponderz

On Friday, November 2, 2012 1:06:28 PM UTC-7, wrote:
In equipment I fly (MD11 with TCAS II) I get azimuth and distance (estimated) with no altitude info. If I'm in Class A airspace, I don't worry about it a lot. Down low, I start looking.

What do you mean by "no altitude info". A TCAS II display is required to encode relative altitude information as a part of the traffic symbol "threat level" choice. And I think its required to have the relative altitude display numbers above/below the symbols. What system/version is in the MD-11?

And since "I get..." is ambiguous as to whether you mean you see on a display or whether the TCAS II system sees relative altitude. TCAS systems do see altitudes of all the nearby aircraft. Or they need to, if its a Mode C rich environment and they suffer from data collisions where the Mode C replies are not readable then the TCAS system quickly becomes useless for those threats (can't issue TA or RA and you may not see any azimuth). The good news is the quadrant antennas and hardware signal decorrelators (that can essentially untangle overlapping transponder transmissions) that TCAS II uses helps reduce problems with Mode-C garbling.

And to answer Eric's question, TCAS I and II would not see mode-A only transponders. They only issue Mode-C interrogations (well they do more for Mode S magic stuff but that does not change the discussion). Not interrogating Mode A helps cut down on wasting bandwidth/garbling and avoid possible Mode C/Mode A code aliasing problems. Anyhow nobody flies Mode-A only transponders anymore.

The bottom line for practical use is if you have Mode C transponder today there is nothing "wrong" with it, keep using it if you fly where transponders should be used. If you are purchasing a new transponder it makes no sense to purchase a Mode C unit today when there are great Mode S transponders available from folks like Trig.

But for ADS-B data-out futures... just don't hold your breath on the FAA making ADS-B data-out easy to install/affordable any time soon, even if you have a Trig transponder.

And if you fly near airliners and fast jets, from a technology viewpoint its not Flarm or ADS-B-data-in or even ADS-B data-out you want, its a Mode C or Mode S transponder that is seen by ATC radar and TCAS I and II. Know local traffic procedures, have your head on a swivel, and talk to ATC where possible/appropriate.

Darryl