http://upload.wikimedia.org/wikipedi..._in_flight.jpg

On 2/14/2015 8:06 AM, Andy Blackburn wrote:
On Friday, February 13, 2015 at 2:47:45 PM UTC-8, Darryl Ramm wrote:
Unlike a transponder UAT Out does not interoperable with TCAS, certainly would never cause an RA to be issued. That big old jet airliner could fly right though you with no warning... its' simply just universally assumed that any aircraft getting near an airliner, fast-jet etc. at a minimum has a transponder (or a transponder and UAT Out, or a transponder with 1090ES Out, but *never* UAT Out only).

This is a critical point.

Most of the traffic out there, if it is carrying any form of ADS-B Out at all, is likely carrying 1090ES Out today (it's the only variant used in Europe and the only variant aircraft flying in Class A in the US carry). The fact that you cannot substitute ADS-B Out carriage for transponder carriage under the regulations is precisely because ADS-B does not activate the RA collision avoidance in TCAS. Take that plus the antenna diversity requirements under the FARs and it seems likely that most aircraft owners in the US will find it easier to equip with a Mode S transponder plus ADS-B 1090 ES Out plus either 1090 ES In or dual-link ADS-B in (it's pretty cheap to provide 1090ES and UAT In "just in case" and to get weather data services - most OEMs are doing this and it would be nice if a future version of PowerFLARM did this too).

I find it difficult to understand why anyone would equip with the duplicate transmitter, antennas, and endure the maintenance, etc, to equip a transponder plus ADS-B UAT Out when the simple solution is to get a Mode S and (at some point) add a (less expensive every day) GPS source to upgrade the transponder to 1090ES Out. The number of scenarios where you are outside ATC SSR coverage but within line of sight to an ADS-R ground station to pick up whatever misguided souls decided to equip with UAT Out only (and not a transponder) are too remote to bother with, and certainly not worth giving up TCAS. Yes, you could always equip with EVERYTHING, but your aircraft will be a porcupine of antennas and it isn't at all clear that you gain very much.

For gliders the best migration path is pretty clear: if you fly mostly with other gliders, get a PowerFLARM, if you fly near a busy airport with a lot power traffic, get a Mode S transponder that can upgrade to 1090 ES Out as the OEMs figure out how to get cheaper GPS sources to market. If you are worried about both scenarios, get both bits of gear.

9B


--
Dan Marotta