Thanks for the write up Jamie. I know that was a serious amount of conversation, education and planning you folks did to pull this off. It is inspiring and shows chat can be done to help improve traffic safety and awareness.

IIRC your club has had Mode-C transponders in tow planes for many years (just so nobody mistakes you did not), which is great, and I assume replacing those old Mode-C transponders was one of the side benefits here. (And sure you can buy a used KT76C for ~500 on EBay... but by the time a replacement is installed and transponder checks are done, and labor and downtime is factored in etc. they may not such obvious bargains).

And a small comment to folk doing similar work with towplanes with 1090ES Out...especially if local powerFLARM users are using Flarmnet (they hopefully are) if you add your towplane's ICAO address to the Flarmnet database that can show up with a "Contest ID" short name on PowerFLARM (with an up to date Flarmnet database loaded) seeing it via 1090ES. The tow-plane does not need PowerFLARM for that to work. That may just help towplanes to stand out more from other traffic... like I worry less if it's a towplane heading towards my thermal full of gliders than some random GA aircraft. Same applies to gliders, so any gliders with 1090ES Out and no PowerFLARM (which I assume would be rare) can still be put in the Flarmnet database.

On Sunday, November 3, 2019 at 6:48:14 AM UTC-8, Jamie Shore wrote:
The Soaring Club of Houston, SCOH, just finished equipping our three Pawnees with Garmin GTX335 ADS-B-OUT transponders. SCOH is located at the edge of the Houston Class B airspace. Occasionally, the towplanes need to fly into the mode C veil to visit maintenance stations. SCOH has a high traffic density of general aviation aircraft routinely transiting our airspace as well as lingering around our airspace for flight training. Thanks to our two, free, FlightAware antennas on our clubhouse roof, we can see the rapidly increasing numbers of ADS-B-OUT equipped traffic. Airliners are right above us and sometimes near cloudbase on good soaring days. Corporate jets also transit our area on a regular basis. Equipping our towplanes with 1090ES ADS-B-OUT equipment was a no brainer since PowerFlarm ‘sees’ 1090ES but does not ‘see’ 978 UTA. SCOH has almost 20 gliders on our field equipped with PowerFlarm.

Below: highlights and excerpts from our communications with club members during our ADS-B Project in 2019.

Jamie Shore
Soaring Club of Houston

The board has approved the installation of ADS-B in all three of our Pawnees. This project is a significant investment in the safety of our operation with a cost of approximately $12,000. Approximately 1/3 of the cost was covered by the club and 2/3 by donations from members.

In the recent past, SCOH had a fund drive for installing PowerFlarm in most of the club owned gliders.

How does ADS-B in the Pawnees fit into the big picture?
PowerFlarm and ADS-B complement each other and they raise awareness in different ways. Currently, three club gliders (both Blanik L23s and the ASK21) are equipped with PowerFlarm. The immediate goal is to maximize the number or aircraft with precision collision avoidance technology - PowerFlarm and ADS-B.

What sees what, who sees who, etc, etc? Partial list below:
SHORT RANGE (couple miles): PowerFlarm equipped aircraft see precise location information for other PowerFlarm equipped aircraft
LONG RANGE (15 miles): PowerFlarm equipped aircraft see precise location information for aircraft with ADS-B “Out”.
PowerFlarm equipped aircraft see a distance for transponder equipped aircraft but NO azimuth (direction)
LONG RANGE: Transiting airplanes with ADS-B “In” see other ADS-B “Out” equipped aircraft with great precision.
Our Pawnees will have ADS-B “Out” but no ADS-B “In”. Our Pawnees will be visible to others (gliders, transiting aircraft with onboard portable devices, ATC, airliners, corporate jets) but there will be no visual display in the Pawnee for the tow pilots to see others.. This will change when we re-install PowerFlarm (or even better an Air Avionics Traffic system) in the Pawnees in the future.

Rationale
The airspace around SCOH is becoming increasingly busy. We have days with 30+ gliders operating and three tow planes moving simultaneously. Add the occasional power plane passing by and the risk factors go up considerably. The modern international standard for all aircraft collision avoidance is now ADS-B. Fortunately it is now becoming economical to install these systems in all aircraft types.
By 2020, flight within or under the Bravo airspace surrounding Houston will require ADS-B compliance. Although this is not an issue for gliders, the towplanes will need to be ADS-B compliant in order to travel into the mode C veil for maintenance. They need to be upgraded at some point and preferably before the 2020 deadline. The only question is with what. There are two types of potential solutions out there. 1090ES, and UAT. They operate on different frequencies. UAT solutions are less expensive initially, but don’t account for a possible need to replace an old transponder in the future. Gliders equipped with FLARM can see 1090ES transponders, but not UAT, and this is an important distinction. Very few aircraft in the GA fleet are equipping with UAT, almost everyone is equipping with 1090ES.
We do have some ADS-B compliant gliders operating from SCOH, and that number will no doubt increase in the future. We have a larger number of gliders that have transponders. From a collision avoidance standpoint, this is nearly as good when operating within Houston Approach Control's operating area because transponder equipped aircraft radar located position is rebroadcast back to all ADS-B compliant aircraft. This makes the collision avoidance hardware presently being installed in most GA aircraft able to electronically see and avoid much of our fleet.
The problem comes in with gliders that are only equipped with FLARM. Although FLARM is able to receive normal transponder signals, this is of very little use in terms of collision avoidance because it does not provide a direction, only a warning that there is a potential for a collision. FLARM does provide accurate collision avoidance with other FLARM equipped aircraft at short range. Since only gliders are involved, this does not help with interactions with the GA fleet as these interactions are one-way in nature. We can see them, but they can't see us. Only ADS-B provides full two-way participation by all parties.

By equipping all of our towplanes with 1090ES systems, we provide several important safety features for the entire SCOH fleet.
All gliders with FLARM, or other GA collision avoidance system installed will be able to electronically locate the towplanes. This is valuable strategic information for inbound glider cross country pilots because unlike FLARM, ADS-B operates reliably at long distances.
GA traffic passing through will see active towplane traffic regardless of whether they can see gliders that are not equipped. This will allow them to be cognizant and avoid our towplanes. When towing a glider, we are particularly vulnerable to near-miss accidents because we cannot react fast enough.
With tow planes in the air that are broadcasting appropriately, this can be made to force traffic information to be active with the system in our local area. This can help "cover" other aircraft that do not have the most sophisticated traffic systems installed (i.e. Stratus and Foreflight within an aircraft with no ADS-B Out).
Increasing the number of aircraft operating from SCOH that are equipped with 1090ES systems will create a cloud of aircraft around SCOH showing up on everyone's traffic display. No GA pilot in their right mind would fly anywhere near our field. There is safety in numbers and we have the numbers, it's just that nobody knows we are there. If Houston TRACON sees this effect, it will have a substantial effect on our ability to maintain our operations over the long term as well. It's pretty easy to push the Bravo out over SCOH, but not if we have an established area of high traffic!

By collecting ADS-B signals from other aircraft, SCOH has a computer in the clubhouse that displays traffic via our FlightAware system. SCOH has two antennas on our roof - both supplied for free from FlightAwa 1) 1090 ES antenna and 2) 978 UAT antenna. Now, we are able to watch, in real time, the position and status of the towplanes, gliders with ADS-B-OUT as well as other transiting airplanes.