TCAS or not TCAS?
 

My 73 T337 G (P model) once had a Ryan 9900BX installed for traffic. A prior owner left the processor in the garage one too many nights and his wife sold it on EBay!

So as I get ready for my avionics upgrade in April, I’m wonderIng if I should find a box and have it reinstalled? It’s already wired for power and antennas and feeds the Garmin 530w.

Rest of the story: In order to get ADSB legal, my upgrade transponder was installed early. As I read about the options it has, it looks like the Ryan 9900BX is not needed at all and that the L3 NGT 9000 unit can use the antennas installed and provide active traffic.

I might be missing something about this technology, can anyone confirm my suspicion that I’ll have active traffic just like from a Ryan unit?

Russ
N8CV

You will only have active traffic in when in range of ADS-B transmitters. There are vast swathes of the US with no radar coverage and no ADS-B either.

ADS-b covers almost 99% of the US, vast swathes with no ADS-b? Maybe if you live in Alaska

That depends on at what altitude you are flying. On an approach below 1500 feet you may not have ads-b coverage. I have attached two screenshots from the FAA ADS-B webpage showing coverage at 1500 and 500 feet AGL.

Ok, I see where you are going with this. I wasn't thinking about the lower altitudes that would be obscured of receiving the 978 UAT transmission. Although it's always nice to be able to know about traffic, the areas that may be obscured are really going to be low volume traffic areas. Most busy traffic locations appear to have coverage. It's easy for me to say as I am now a flatlander pilot and have coverage nearly 100% of my area. Point taken, thanks Ed

Russ

L3 is local here in GR and I have contacts with some of the folks if you think that would help to answer some questions. Not sure I totally understand what you are asking as I am familiar with the Ryan systems

Tcas
 

Thanks for both of your responses!

What I refer to as ‘active traffic’ is when an airplane with an active XPDR interrogator onboard sends a query which is replied to by another aircraft transponder. I called it ‘active’ because of a transmitted signal from the equipped plane. I understood the Ryan 9900bx (or Avidyne 600) to be this type of system that actively interrogated itself, stimulating a response from traffic.

Other systems may receive transponder signals and give a general idea of location and range based on signal strength and the diversity signals between two antennas. These are passive systems and rely on some other query signal to stimulate the traffic plane’s XPDR.

I believe the L3 transponder has the same function as the Ryan 9900bx when attached to the diversity antennas. My avionics installers think they will be able to do this simply by unlocking the option in the NGT9000 transponder and connecting it to the existing antennas. I guess I’ll find out in April after the Exumas trip, and while recovering from Achilles’ tendon repair surgery!

ADS- B reception dead spots I think are very few over land. I’ve heard that soon the satellites will be in place to pick up these signals worldwide.

I’ve built three ADS-B receiver stations and connected them to the internet becoming part of the ground system. I gave one to a friend in Tuscaloosa, have one in my home in Georgia, and gave the third to my avionics shop last week so they could get registered and qualify to get the commercial version of FlightAware for free.

There were still a lot of dead spots in the VIrgin Islands last time I looked at my tracking station software. I don’t spend much time with the site, but there are a lot of statistics and measures available if you are really bored or just ultra competitive!

Russ
N8CV

That makes sense now Russ. Using the existing antennas to activate the TCAS on the new L3 unit. If that works that would be great. Hoping it all comes together for you

My take on TCAS vs ADSB vs having both
 

I think the real question now is,

"Do enough aircraft now have ADS-B out
to become reliably and directly visible to other aircraft,
in areas of no ADS-B ground stations?"

My Ryan is sick, and I am wrestling weather or not to fix it for $4k
(About what it cost to install, BTW).

9900 BX TCAS (AVIDYNE)

For years I have had a 9900BX which interrogates ALL 1090 traffic within 30 miles,
and a pleasant little voice that tells me if anything is interesting.

It is like having built-in radar flight following.

The interrogating 9900BX (or re-labelled Avidyne) sees EVERYTHING that emits 1090Mhz,
Mode S AND Mode C.

NGT9000

I understand the NGT9000 has a golden-screwdriver unlock that interrogates like the TCAS. When I checked into it, it also requires a $3k Skywatch antenna. Open to updates~!

==

ADS MOOSH

The evolution of these programs has created a mish mash.
While you get a lot of data, you really don't know what's missing.
It is a cloud of visible and missing targets.

Go back to elementary school Venn diagrams. (Wild top-of-head approximations here):

98% of airliners have BASIC 1090 Mode S transponders 1090 MHz
Invisible to 978Mhz UAT
Invisible to 'dual mode' 1090 listening devices (because no position info in C or S)

Only visible in ADSB world if
Ground based radar observes and ADSB ground station sends back out

2% of airliners have Mode S extended squitter ADSB 1090 Mhz
Invisible to 978Mhz UAT
Visible to 'dual mode' 1090 (Because extended HAS position info)

Airliners fly IFR so for the most part ARE visible to radar
so WILL be sent out from ground ADS stations, if YOU are within station range.

Otherwise one can pass off your nose and ALL our black boxes will never see it,
EXCEPT an interrogating Ryan or NGT 9000.

70% of GA aircraft have ADS-B out UAT 978 Mhz
Invisible to TCAS 1090 MHz
Visible to RADAR if within radar coverage
Visible to UAT IN 978 MHz

5% of GA aircraft have ADS-B out Mode S extended 1090 Mhz
Invisible to UAT in, unless observed and relayed by ground station

===

Mode S = aircraft ID, Altitude, squawk = no position
Mode C = altitude, squawk
Mode S Ext= aircraft, altitude, squawk & ads-B = position
UAT OUT= 978 Mhz = blind to the entire 1090 world w/o nearby ADS ground station
UAT IN = 978 Mhz = blind to the entire 1090 world w/o nearby ADS ground station
Dual Mode = Listens on 978 UAT and 1090 (but only sees Mode S extended w position)

Airlines have been exempted from ADS-B Mode S extended squitter,
so don't hold your breath to seeing them on your UAT IN anytime soon.

==

Funding for ADS B was justified by FAA (and the USAF)
as a way to get the private sector to buy the replacement
for areas of dying FAA radars. So it has lots of holes.
And likely to stay that way.

USAF is trying to get control of the $15b from the spectrum sale of 5G to put in more radars
Which might, or might not happen.
So CONUS coverage might get better IF USAF feeds that data to FAA for distribution over ground stations.

So down low, or out of ground-station coverage, TCAS the only way to go.
There may be lots of traffic, but you may be missing a lot of it.

What a mess!

TCAS continued
 

Thanks for the info David.

If you have the Ryan 9900bx already installed, don’t you already have multiple antennas to support it? Do you know if they can be re-purposed to support an NGT 9000? I was under the impression they could and that was my plan.

One thing you didn’t mention is the satellite-based reporting for ADS-B. I thought I read somewhere that there would be sufficient coverage for that system in 2020?

Reading the NGT 9000 manual, software to omit targets that present no threat seems to be a specific intent of the NGT 9000. I noticed flying the last few days that my iPad with ForeFlight attaches to the NGT 9000 WiFi, has a lot more contacts than on the NGT 9000 itself.

I also noticed the ForeFlight displays 10m accuracy on the iPad when I’m using the 9000, but alone with its internal antenna, the iPad claims 5 m (and down to 1M with my Stratus 2s).

I guess I’ll find out more in April during the actual installation.

Russ
N8CV