uAvionix TailBeacon: Installation and Testing

TailBeacon of uAvionix mounted on rudder of Zenith 601HDS

The uAvionix TailBeacon is a low-cost device that satisfies the ADS-B Out requirement kicking in on January 1, 2020. 

The TailBeacon piggybacks on any Mode C or S transponder, and thus avoids purchase of a much more expensive ADS-B transponder. 

There are two TailBeacon versions: the TailBeacon TSO for certificated aircraft and the less expensive TailBeacon EXP for experimental aircraft. 

We bought the EXP version for our Zenith 601HDS, N314LB.

uAvionix also offers an alternate ADS-B Out module: the SkyBeacon. It uses similar technology, but is installed in a different part of the airplane. Details on this below. There are two versions: TSO and EXP. 

This post covers why we selected the TailBeacon and how we installed, tested, and evaluated it using the FAA ADS-B Performance Report. It's easy to adapt the process for installation of the SkyBeacon.

Want to learn more about flying?

  

My book Lessons from Piloting for 45 Years covers close shaves over more than four decades involving thunderstorms, mountain weather, faulty runways, equipment failures, and more.

Learn key strategies for coping with these dangerous situations. They include two tools called Sully's Rule and Forecast Evaluation.

ADS-B Out Requirement

Starting on January 1, 2020, every airplane in the US must have ADS-B Out if flight is conducted

– within class A, B, or C airspace; 
– within the 30 nm veil of Class B space;
– if flight is in Class E airspace at or above 10,000 ft MSL unless conducted below 2,500 ft AGL;
– in Class E space over the Gulf of Mexico at or above 3,000 ft MSL within 12 nm of the US coast.

These conditions match those calling for an altitude encoding transponder, except for the additional Gulf of Mexico condition.

There is another factor motivating installation of ADS-B Out. Suppose you fly over some remote area and the engine quits. You make an emergency landing.

Let's suppose you are okay, but you aren't able to hike out. Now you worry. How quickly will rescuers locate you?

If the flight is conducted with ADS-B Out, there is a complete track of your plane, and no matter how you deviated from the flight plan and for whatever reason, rescuers will find you quickly.

The Decision

Our plane has a Bendix King KT 76A transponder that has performed reliably for almost 2,000 hrs. Tens of thousands of this model have been produced and installed. 

Since pilots now and then switch to newer, fancier looking transponders, there is a large supply of used KT 76A transponders on the market. So, if a repair ever becomes too costly, we will always be able to find a used replacement.

Based on this reasoning and the fact that we already have ADS-B In via Garmin GDL 39 and iPad — installed five years ago — we decided to get additional equipment for ADS-B Out that piggybacks on our KT 76A transponder.

There are three major choices: the Garmin GDL 82 and the two uAvionix modules mentioned earlier: the TailBeacon and the SkyBeacon. We opted for the TailBeacon since it seemed easiest to install.

We ordered the TailBeacon from Sarasota Avionics. They handled everything efficiently, including a related purchase described later. Sarasota Avionics  thus has become our favorite supplier for aircraft electronics. 

uAvionix

The ADS-B Out modules supplied by uAvionix replace either the left wingtip navigation light (SkyBeacon) or the tail navigation light (TailBeacon).

In principle, one simply removes the existing wingtip or tail navigation light, hooks up the uAvionix module, and attaches the module to the wing or tail.

SkyBeacon or TailBeacon?

The SkyBeacon replaces the left wingtip light. If that light also has an integrated strobe light, as is the case for us, then one would want to select the SkyBeacon with integrated strobe and replace the right-wing light/strobe by a matching uAvionix navigation light/strobe. 

In addition, all the existing strobe equipment must be removed and the wiring adapted accordingly. Surely a major operation, and due to the two replacements, rather expensive.

In contrast, the TailBeacon requires just replacement of the tail light. Sounds much easier, right? So we went for that choice.

Important Check

If you decide to get the TailBeacon, do one important check before you place the order: 

The top of the existing tail light must be free from obstructions. 

If that is not the case, you cannot use the TailBeacon since its GPS antenna will not be able to receive the satellite signals.

TailBeacon Installation

The uAvionix advertisement describes the installation of the TailBeacon as a 10-minute project. In principle, that claim is correct.

But if you want some features that we deem essential, it is quite a bit more work. In fact, we spent 8 hours. 

Choices, Choices

When the TailBeacon is installed as described by uAvionix, the navigation lights must be turned on all the time. 

But our incandescent wingtip navigation lights draw considerable current relative to the modest capacity of our Rotax 912 alternator. Thus, turning them on all the time is not a good choice.

Here is the way out: 

We separate the electrical supply to the tail light from that of the wingtip lights. We then view the wingtip lights as navigation lights as before, but consider the TailBeacon to be one of the avionics devices — radio, transponder, etc. — that are always turned on.

Given that decision, there is a natural choice for powering the TailBeacon: We go from the avionics master switch to a separate panel switch labeled "ADS-B," and from there to the TailBeacon. 

Unless there is some unusual situation, such as an alternator failure, the ADS-B switch is always turned on.

We have been told that uAvionix is not allowed to recommend use of a separate ADS-B switch. The reason, we guess, is that performance of the TailBeacon cannot be monitored in flight. 

But omission of the switch is not a good choice. You want to be able to isolate an electrical in-flight failure by selectively turning off equipment. That should include the TailBeacon.

Of course, the setup must be such that the TailBeacon is automatically turned on in normal operations. You achieve this by wiring the TailBeacon into the avionics master switch and leaving the ADS-B switch turned on as default, just as you do for the transponder.

This setup requires some rewiring. 

Wiring Steps

Some 23 years ago, we didn't wire the tail light directly to the navigation light switch. Indeed, that wire goes from the tail cone into the left wing where it is connected to the wire going to the left wingtip light. 

It doesn't make sense to pursue this wire into the wing. So we simply cut the wire were it transitions from the tail cone into the left wing. 

We secure the end of the now-unused wire with shrink tubing and label that end for future reference with "OLD TAIL LIGHT." 

The other end of that cut wire is extended and goes to a new panel switch labeled "ADS-B" and from there to the avionics master switch.

Switches: "Auto" for TruTrak autopilot, "GDL" for Garmin GDL 39, and new "ADS-B" for uAvionix TailBeacon.

Sounds easy, but it is a lot of work. We do this very slowly and carefully, to make sure that there will never be an electrical problem.
 
Let me pause for a moment to introduce one of my arguments justifying personal aviation.

Justification of Personal Aviation

Slow, deliberate work on the wiring as well as for any maintenance or repair increases our earnings, based on the following theory. 

Whenever we work on the plane, we earn for ourselves money at the going rate for airplane maintenance, now at least $85/hour. 

So working slowly not only results in high-quality results, but also boosts our income. 

If you are an airplane builder/pilot, you may want to use this argument when your spouse talks about the considerable expense of building and maintaining an airplane. 

"No, no," you should say, "with all these hours of work, we are making a lot of money!"

Replacement of Tail Light with TailBeacon

It sounds so easy: Unscrew the old tail light, cut the two wires, connect them to the TailBeacon, and attach the TailBeacon to the tail cone.

Well, in our case it was a bit more involved.

TailBeacon assembly. © 2018 uAvionix, which kindly granted permission to use the drawing.

Two Messages of Caution

First, when you cut the wires of the old navigation light, make sure that they do not slip into the tail cone, unless you are fond of fishing for wires through the small hole where the tail light used to be.

Second, before you hook up the existing tail light wires to the TailBeacon, do some checks covered next, unless you like unpleasant surprises.

Check Hole Diameter

Do not trust the existing hole for the tail light to be big enough for the TailBeacon. 

It looked perfect in our case, but the hole was actually too small. The correct hole diameter is 29 mm, which is just a bit less than 1 5/32 in.; see below. 

Mounting Ring. © 2018 uAvionix, which kindly granted permission to use the drawing.

If the hole is too small, use a Dremel with small sanding drum to enlarge the hole. Make sure you are not damaging the two wires sticking out of the hole by using the following process:

Cut a short piece of PVC pipe with 1 in. outside diameter lengthwise. You get two pieces. Ignore one of them, and insert the other one into the opening so that the piece covers one half of the hole plus the two wires. 

Then use the Dremel drum on the exposed half. When done, cover up the enlarged half and the two wires, and enlarge the now-exposed half.

Check Position of Nutplates

The existing two nutplates for the mounting screws must be lined up horizontally or vertically. Below, we cover the two cases where the nutplates do/don't line up.

If Nutplates Line Up Horizontally or Vertically

Do not trust that the two #4 mounting screws supplied with the TailBeacon are correct for the nutplates. 

Most likely the screws are too small, as was the case for us: The screws for our tail light were #6, a typical size.

What to do? Instead of hunting for new nut plates, we enlarged the two holes in the mounting ring of the TailBeacon to 9/64 in. — the appropriate hole for #6 screws  — then countersunk the enlarged holes so #6 flat-head stainless-steel screws could be used.

Do all this very carefully and slowly. 

In particular, make sure that the holes are sufficiently countersunk so the heads of the screws do not stick out beyond the surface of the mounting ring. 

If that is not done, you will not be able to install the module properly.

If the screws for the existing tail light are larger than #6, do not do the above process. 

Instead, install nutplates for #4 and use the supplied screws. Or, if you have trouble getting such small nutplates, settle on readily available #6 nutplates, and use the above process.

If Nutplates Don't Line Up As Required

You must install new nutplates that line up either horizontally or vertically, your choice. 

The size of the nutplates depends on whether you will use the supplied #4 mounting screws or go to new #6 screws. 

In the second case, you need to modify the mounting ring as described in the above section.

Check Small Set Screws

The module is secured to the mounting ring by two, truly tiny, set screws M2 x 4mm. In our case, they were binding in the threads of the mounting ring. 

So clamp the mounting ring in a vice, with protective wood blocks, then insert the screws and turn them with the supplied 1.5mm Allen wrench. 

If they do not easily turn, apply a bit of lubricant and try again. Repeat this until the screws turn easily.

Mounting the TailBeacon 

The rest is easy. Remove the paper that covers one side of the supplied rubber gasket for the mounting ring; see the above drawing. 

Stick the gasket with the gluey side to the mounting ring.

Attach the mounting ring to the tail of the plane using two flat head screws.  

If you use #6 screws, the two holes in the rubber gasket may seem too small. But never mind, you will be able to push the screws through the seemingly too-small gasket holes.

Connect the wires to the module with the supplied crimp connectors. 

The mounting ring has a bayonet connection for the module. Insert the module all the way while keeping the two antennas at a slant so that, when you twist the module 45 deg clockwise, it engages the bayonet connection and the antennas become vertical, with the larger antenna pointing down. 

Finally, insert and tighten the supplied tiny set screws so that the module is fixed in the mounting ring.

Weight and Balance

The entire TailBeacon weighs 70 grams. In our case, this is almost a match of the 50 grams of the removed tail light.

Thus, the effect on weight and balance of the plane is negligible and need not be computed.

Theft Protection

The uAvionix TailBeacon is the only expensive device mounted on the outside of our plane. It can be removed by unscrewing two Allen head screws and cutting two wires. What's preventing a thief from doing this?

First, damaging an airplane is a federal offense (18 U.S. 32). There is a good reason for this law: Any damage might result in a fatal accident.

Second, the two Allen head screws securing the TailBeacon module are truly tiny: The size of the wrench is 1.5mm. A thief is unlikely to have such a wrench.

Third, the TailBeacon produces a WiFi signal that is used to set and change parameters, such as the N-number. 

The access requires a password that is supplied with the TailBeacon. A thief would not have the password, hence the module is useless when installed in any other aircraft.

We wish, though, that uAvionix had not printed their logo on the antenna of the TailBeacon. Why advertise that this is a piece of electronics? 

Were it not for that logo, the TailBeacon would look like any old tail light and wouldn't invite theft.

We are ready to set certain parameters for the TailBeacon.

Set TailBeacon Parameters

You can download the free uAvionix app for the SkyBeacon/TailBeacon into any Apple or Android device. Just go to the App Store or Google Play.

We did so for our iPad, which we use with the Garmin GDL 39 for navigation, and our Android cell phone. 

The icon of the app shows a picture of the SkyBeacon. But don't fret, there is nothing wrong: The app works just as well for the TailBeacon.

You set certain parameters in the TailBeacon with the app. We used the iPad for this since it has a larger display.

You need to obtain some information before you start the app.

Get ICAO Number

Each aircraft registration number has an equivalent ICAO code. You need that code in hexadecimal notation. 

You get it on the FAA Registry website. Just enter your N-number and click on "Submit." 

The next page shows the desired ICAO code under "Mode S Code (base 16 / hex)."

Measure Displacement of TailBeacon

Measure the displacement of the TailBeacon to the left or right from the longitudinal axis of the airplane; the displacement likely is equal to 0.

Measure the distance from the nose of the aircraft to the TailBeacon. If you measure this in feet, convert this to meters. Round that number to the nearest integer. In our case, the distance is 6 m.

Connect to TailBeacon

Power up the TailBeacon. It outputs a WiFi signal. Turn on your tablet or smart phone. 

In Settings of your device, the WiFi of the TailBeacon shows up as "Beacon-xxxx". Connect with Beacon-xxxx using the password supplied by uAvionix.

Initialize TailBeacon

Start the uAvionix app. For a second, you see a photo of the SkyBeacon, and then the following page.

Start page of TailBeacon app

If you have set up the WiFi connection correctly, this page disappears after a moment and a new page pops up. 

It has at the bottom two options: "Configure" and "Monitor." The app starts with the "Configure" page. If not, tap on "Configure."

The "Configure" page has two options shown at the top of the page: "Basic" and "Advanced." Go to "Basic." 

Configure Basic

Configure Basic

You must specify the following.

Transmit Enabled

This must be enabled so that the TailBeacon does transmit ADS-B Out.

Anonymous Mode

Selection of anonymous mode is effective only if the transponder code is 1200. In that case, the ADS-B output is not accompanied by your N-number and ICAO code, but by a randomly selected code.

Anonymous mode must be turned off for testing of the TailBeacon.

When VFR flight is conducted under a flight plan, the anonymous mode must also be turned off.

Anonymous mode does not imply that air traffic control does not have your N-number and ICAO code, since that information is broadcast during taxiing and the first few minutes of flight even if that mode is turned on. 

Indeed, air traffic control keeps that information attached to your entire flight trajectory even though anonymous mode transmits randomized codes for the remainder of the flight. It's just that other pilots and third parties on the ground do not have that information and cannot track your flight.

Call Sign  

Type in the N-number, including the "N." In response, the app fills in the ICAO hexadecimal equivalent on the next line. Compare that number with the one you determined earlier, to make sure it is correct.

Vso

Specify the stall speed of the aircraft in landing configuration. The number is used by the ADS-B system to differentiate between ground operations and flight. 

ADS-B In Capability

Select the appropriate specification. In our case, the Garmin GDL 39 supplies ADS-B In data for both frequencies 1090 MHz and 978 kHz.

When you are done, tap on "Update" to store the input data.

Go to "Advanced." 

Configure Advanced

Configure Advanced

Position Light

Turn on if you have navigation lights for the wings. The TailBeacon supplies the navigation light for the tail.

Anticollision Light

Turn on if you have anticollision lights. Our plane does so for the wings.

Emitter Type

Select the aircraft category that most closely matches the aircraft. For small planes such as ours, the category is "Light Airplane."

Aircraft Length (m)

Select the appropriate category for the length. In our case, the smallest category, with L ≤ 15, applies.

Aircraft Width (m)

Select the appropriate category for the width. In our case, the smallest category, with W ≤ 23, applies. 

Specify the position of the TailBeacon using the displacements you determined earlier. There are two sliders for this.

GPS Antenna Offset 
Lateral from roll axis

Tap the dot of the slider and move it to the position so that the displacement of the TailBeacon to the left or right of the longitudinal axis of the plane is shown. For our plane, the displacement is 0.

GPS Antenna Offset 
Longitudinal aft from nose

Tap the dot of the slider and move it to the position so that the distance of the TailBeacon from the nose of the plane is shown. For our plane, the length is 6 m.

The next category is a bit more complicated. So before going on, tap on "Update" to store the input data.

Transponder Monitor Threshold

A default value is shown. In our case it was "42". That value may not be correct. We discuss next how to determine the correct value.

When your transponder is interrogated by a radar signal, it outputs the transponder code and, if in ALT mode, the pressure altitude. 

The TailBeacon uses an ingenious method — patented by uAvionix — to obtain the transponder code transmitted by the transponder. 

Each such transmission induces voltage fluctuations in the aircraft wiring. The voltage variations are very small and do not interfere with other electrical equipment. 

The TailBeacon analyses these voltage changes and extracts from them the transponder code. Amazing that this can be done, isn't it?

The Transponder Monitor Threshold is needed by the TailBeacon to decide which voltage changes in the aircraft wiring are random noise and which convey the transponder code.

The threshold value depends on the strength of the transponder signal. Newer transponders are more powerful, while older ones, like our KT 76A, are less so. 

uAvionix recommends the value of the threshold to be between 30 and 42. The default value was 42 in 2018, but according to a recent SkyBeacon installation carried out by airplane guru Jack of Aero Country airport and us in early 2019, was then changed to 35.

How do you determine the correct value for your plane? The answer below refers to the Monitor page, which you reach by tapping on the "Monitor" icon at the bottom of the page. 

Here is that page, without any performance data except for the pressure altitude, since the screenshot was taken in the hangar.

Monitor page

It is prudent to compare the displayed pressure altitude value with the pressure altitude of your altimeter. For the comparison, reset the pressure of the altimeter to 29.92 in. 

If the altitude of the altimeter differs from that of the Monitor page more than 125 ft, it is likely that the altimeter must be recalibrated. 

But take no action yet. Instead, recheck this after the first test flight, since the TailBeacon continuously recalibrates itself in flight using the transponder-reported altitude. 

Any difference larger than 125 ft after that test flight means that the performance of the altimeter and the encoder of the transponder must be investigated.

The recalibration process also implies the following: You can always test the performance of the altitude of the encoder on the ground by setting the altimeter to 29.92 and reading the reported pressure altitude of the TailBeacon. That is a neat feature.

This check does not satisfy the requirement for VFR flight that encoder and altimeter be tested every two years. But nevertheless it is an easy test to carry out now and then to confirm that TailBeacon, encoder, and altimeter produce correct pressure altitude within the allowed deviation.

Options for Determining Transponder Monitor Threshold

There are three options for determining the Transponder Monitor Threshold.

1. Radar Signal Available at Your Airport

If you have a radar signal at ground level at your airport, move the aircraft so that it is exposed to the signal. 

Turn on the transponder and the TailBeacon. The radar signal should interrogate the transponder at least every 18-40 seconds, as can be verified using the indicator light of the transponder.

In the app gradually modify the threshold using the slider for Transponder Monitor Threshold.

Start at 42. Go to the Monitor option of the app by tapping on the Monitor icon at the bottom of the page, and check whether the transponder code is shown under "Squawk." If the transponder code is shown, you are done. 

Otherwise lower the value from 42 in decrements of 3-5, stopping at 30. Each time check the effect on the Monitor page. 

Once you reliably see the transponder code on the Monitor page, tap on "Update" to store the input data.

2. Signal from Transponder Test Set

If you have access to a transponder test set, do the above process while the test set generates the radar signal.

In addition, use the transponder ALT option to obtain the pressure altitude transmitted by the transponder. Compare that number with the pressure altitude transmitted by the TailBeacon. That altitude is shown on the Monitor page. 

The numbers should be close due to the recalibration feature of the TailBeacon; see the earlier discussion about that aspect. If the two numbers differ substantially, contact uAvionix Support and ask for assistance with the investigation.

3. Signal Unavailable

If you do not have a radar signal at the airport at ground level and do not have access to a transponder test set: 

Just use the default value, which in early 2019 was 35. If you have equipment of older inventory, there may be a value of 42, as happened in our case. The latter value did not work for us, but a switch to 35, as recommended by uAvionix, resulted in perfect performance.

Tap on "Update" to store the threshold value.

At this point, you have completed the initialization process of the TailBeacon.

Next is testing. First, on the ground, and then in flight.

Ground Test

Move your plane to an open area, away from hangars and other buildings. Turn on the TailBeacon and the uAvionix app, and go to the Monitor page.

The Identification section of the Monitor page shows the N-number you have inputted and the equivalent ICAO Number. 

If there is a radar signal at ground level, the Squawk code shows the transponder code. Otherwise, the Squawk code is indicated as missing by "--".

The Position section shows a value for Altitude Pressure.

After maybe 2-3 minutes, the Position section should show values for Latitude, Longitude, and Altitude GPS.

If this still isn't happening after 5 min, you likely do not have an unobstructed view of the GPS satellites. Move the plane away from obstructions and repeat the process.

If you still are unsuccessful, contact uAvionix support. They will ask about the System Status light, explained next.

System Status Light

The TailBeacon has a red System Status LED light on the right hand side. According to the uAvionix manual for the TailBeacon, the light is interpreted as follows:

– On (constant): no failure.
– Blinking: Function failure. No GPS signal. ADS-B broadcast failure.
–  Off: Device failure. Internal self-test failure. Invalid OCSO configured.

The case of blinking light is readily explained if the TailBeacon does not have an unobstructed view of the sky. 

But if this does not apply, contact uAvionix support for help. Do this also if the red light is off.
  
Flight Test

The flight test must be conducted near an area with good radar coverage, such as class B or C space. The key for success is complete adherence to the instructions below.

Taxiing and Takeoff

Taxi from the hangar to an open area of the airport and stop. Turn on the transponder with ALT option and the TailBeacon, besides all the other equipment you use for flight.

Wait at least 3 min, preferably 5 min, before you taxi for takeoff. This allows the TailBeacon to acquire the GPS satellites.

Taxi slowly to the runway, just as you did when you first learned to fly.

Take off in a gentle manner, climb at a reasonable rate, say 300-500 ft/min, and fly away from the airport. If you turn, do so with gentle turns, such as 15 deg.

Maneuvers 

Generally, this is not the time to impress anybody with your piloting skills. 

Fly at least 3,000 ft AGL so that you surely will be within radar coverage. If you started under class B space, as in our case, move slightly beyond the outer limit of the class B space so that you don't enter it inadvertently.

Do some gentle maneuvers: Modest climbs and descents, and shallow turns. Include at least two 360 deg turns, of which at least one must be to the left and one to the right. 

The entire maneuvering portion of your flight must take at least 10 min. The entire flight must be at least 30 min.

Landing

Return to the airport and land, again with gentle changes of altitude and direction. 

You must come to a full stop on the runway. If this is a controlled airport, get permission from the tower to do so, by explaining that this is an ADS-B test flight.

Evaluation of Test Flight

Go online to request an FAA ADS-B performance report for the flight. The page asks your for details about the flight.

Specify
– Date of flight start;
– N-number with leading "N";
– "UAT" as ADS-B Out data link;
– full name;
– email address;
– "uAvionix" as manufacturer, "tailBeacon EXP" or "tailBeacon TSO", whichever applies, as model;
– first GPS manufacturer as "internal", model as "internal";
– second GPS manufacturer as "not installed";
– installer as appropriate.

When done, click on "Submit Request." Within 30 min or so, the FAA will send the performance report to the specified email address.

Interpretation of Performance Report

The report has statistics about the ADS-B Out transmissions of the test flight. Boxes shaded red indicate unsatisfactory performance. 

The most likely problem is in the section "Other Checks" of the box "Mode 3A." The latter term refers to the transponder code.

Here is the case we encountered.

The red box indicates that for 43.98% of the transmissions, the transponder code did not agree with the TailBeacon code. 

The max time of consecutive failures was 6:17 min, and the max number of consecutive failures was 374.

That massive failure rate occurred when we set the Transponder Monitor Threshold at 42. 

uAvionix Support then advised that we should reduce the threshold to 35. This produced perfect test results for Other Checks Mode 3A. But it also produced another error, to be discussed later.

How stable is this choice? To evaluate this, we conducted two test flights with threshold values below and above 35. We chose 33 and 37. 

Both values resulted in perfect reading of the transponder code by the TailBeacon, proving that 35 is indeed a stable choice.

Later we talked with friend and airplane guru Jack about this problem. We then became aware that he had transponder testing equipment. 

Indeed, he helped us verify with the testing equipment that the value 35 results in complete agreement of transponder and TailBeacon codes. 

As a bonus, we also established that the pressure altitudes of transponder and TailBeacon differ by only 25 ft.

The transponder monitor thresholds 33, 35, and 37 resolved the Mode 3A errors. But at the same time, another major error surfaced.

A Nasty Complication

From the second test run onward, the performance report showed a huge failure rate of 93.71% for the Flight Id category, as shown below.

Performance Report with huge failure rate for Flight Id

The Flight Id is just the N-number, which is manually inputted into the TailBeacon as described earlier. How could any error involve that entry?

To the rescue came Ryan of uAvionix. He explained the TailBeacon operation, and how the rules could result in the massive error rate for Flight Id.

TailBeacon Operation

First, the TailBeacon computes the pressure altitude and includes that value in a certain position of the ADS-B output. 

That same position is also reserved for the Flight Id. There is an additional 0/1 value that tells whether the information in that position is the pressure altitude or the Flight Id.

In the regular operation, the TailBeacon includes the Flight Id in one output message, the pressure altitude in the next one, the Flight Id in the subsequent one, and so on in alternating fashion. Let's call this the "alternating process."

Second, the TailBeacon obtains not just the transponder code via the aircraft wiring, as described earlier, but also the pressure altitude broadcast by the transponder.

The TailBeacon compares the transponder altitude with one it computes internally. 

If the two numbers match, all is well: The alternating process outputs the TailBeacon-computed pressure altitude and the Flight Id. 

If the two altitude numbers differ by a small amount, the TailBeacon uses a recalibration process to adapt to the transponder-reported altitude. 

But if there is a huge gap, the TailBeacon suspends the alternating process and in the next five output messages includes only the transponder code and never the Flight Id.

If It Can Go Wrong, It Will

We had a freaky occurrence with our installation. The altitude encoder of the transponder worked during the very first test flight, but stopped entirely during all subsequent flights. 

Thus, the TailBeacon did not receive any transponder altitudes during each of the subsequent flights, and had nothing to compare with the pressure altitude computed by the TailBeacon. 

This caused the TailBeacon to suspend the alternating process. Accordingly, it included in the ADS-B output the transponder code all the time, and never the N-number.

Well, "never" is not quite correct. The rule suspending the alternating process does not apply early-on in the flight, so the initial portion of the flight did have the Flight Id often enough that the ADS-B ground station could tag our flight trajectory with the N-number, and thus could send us a performance report.

Once we had the explanation provided by uAvionix, the solution was simple. We removed the ACK-30 Mod 3 altitude encoder of the transponder from the airplane and asked avionics guru Dick of the local avionics shop to bench test it. Indeed, the encoder didn't work at all. 

We obtained the replacement ACK-30 Mod 5 from Sarasota Avionics. To make sure that all was well, Dick bench tested it and found it to be in perfect condition.

ACK-30 Mod 5 altitude encoder

The ADS-B Out test flight with the new encoder resulted in a performance report with perfect results. At last, we had a functioning ADS-B Out system.

What To Do If You Fail the Performance Test

The email of the FAA with the performance test data also contains an email address for help. You send the performance report to that address and ask how you should fix the deficiency.

Typically, FAA personnel will respond rather quickly and will advise you about remedies. The recommendation quite often will be that you should contact the supplier of the equipment, in this case uAvionix.

Two Words of Advice 

First, before you install the TailBeacon, go ahead and check the transponder and its altitude encoder so that correct information is produced. That wouldn't have helped in our case, since the failure of the encoder happened only on the second test flight. But barring that rare event, such checking surely simplifies testing the performance of the TailBeacon.

Second, the uAvionix company is located in Montana. Support starts at 9 am Mountain Time. Call shortly thereafter, before a queue of inquirers has developed.

Installation of SkyBeacon

All of the above steps for the TailBeacon apply to installation of the uAvionix SkyBeacon, except that the left wing light is replaced by the SkyBeacon. 

Of course, one then must also consider how wing strobes are handled. 

And one must also make sure that the engine is never started or stopped with the navigation lights on. 

As described above, we assure this for the TailBeacon by wiring it to a separate ADS-B switch powered by the aviation master switch.

Regular Operation

What do you do once you have installed the TailBeacon, have tested it, and are ready for regular operation?

Here is a suggestion. When you have started the engine of your plane and have turned on the TailBeacon via the Avionix Switch, do not allow the aircraft to move. 

Switch the transponder to the ALT setting. 

Check that WiFi of the iPad is turned on and verify that it is connected with the uAvionix TrailBeacon.

Go to the uAvionix TailBeacon app and check that it displays the transponder code. If so, you have reasonable assurance that the TailBeacon operates correctly.

Why should you do this check? There are two reasons.

At some time after January 1, 2020, the FAA will begin enforcing that ADS-B Out works correctly on all aircraft, including yours. 

The suggested check does not really verify this, since this is not a flight test. But if you are told that ADS-B Out of your plane is not correct, you can argue that before each flight you do check the operation of the TailBeacon to the extent available to you.

The second reason is just as important. If your TailBeacon is not working correctly, you will not get the expected ADS-B In data telling you about aircraft approaching your plane. That information can be crucial as we found out twice during just one cross-country flight.

Why is it important that you do not allow the aircraft to move during this check? As soon as the TailBeacon senses, via GPS data, that the aircraft is moving, it shuts down the WiFi connection, as mandated by the FAA.

Altimeter Check

The information displayed about other aircraft allows you to check whether your altimeter is correct at any altitude. 

This is important for planes used only for VFR since the recertification of encoder and altimeter every two years is only done on the ground at whatever barometric pressure is present.

For the check, climb to the altitude where you want to perform the test. 

Temporarily reset your altimeter to 29.92. It now displays pressure altitude. 

Select a nearby aircraft displayed by ADS-B In. Obtain details for that aircraft by whatever process is appropriate for your ADS-B In system. 

For example, the Garmin Pilot displays a positive or negative number D that is the altitude difference between that aircraft and your plane. If D is positive, the aircraft is above you, otherwise it is below.

For the Garmin Pilot, click on the icon for the aircraft. It opens a circular window. Click on the icon of the aircraft within that window to get the information. It includes ground speed and pressure altitude P of the aircraft.

Then your altimeter should show altitude = P - D.

For example, if P = 3100 ft and D = 1000, then the aircraft is 1000 ft above you, and your altimeter should show  altitude T = P - D  = 3100 - 1000 = 2100 ft.

If your altimeter displays a very different value, say with the difference exceeding 150 ft, then either your equipment is faulty or that of the other plane. You can eliminate the latter case by doing the above process for some additional aircraft.

Important: When you are done with the check, reset your altimeter to the current barometric pressure.

Simplified Altimeter and TailBeacon Test

These days, IFR flights often are done more or less exactly at odd or even thousands of feet MSL. That's due to the fact that many planes flying IFR use an autopilot maintaining altitude. You can use this for a quick test of both your altimeter and the Beacon.

When you see a plane on the Garmin Pilot or equivalent, assume for the moment that it is IFR and at an IFR altitude. Then your altimeter reading plus the altitude difference indicated by ADS-B must be more or less equal to an IFR altitude. 

For example, if ADS-B shows the plane as 1,500 ft above you and your altimeter indicates 4,500 ft MSL, then 4,500 + 1,500 = 6,000 is indeed an IFR altitude. 

The agreement need not be perfect, indeed may not exist at all since this actually may not be an IFR flight or is an IFR flight that is changing altitude. But by repeating the process a few times for several planes shown on ADS-B, you will find a number of cases where you identify an IFR altitude, and thus have verified that both the TailBeacon, the altimeter, and the encoder of the altimeter are working correctly.

We do this test each time we are on a long cross-country trip. It's fun to do and checks both your altimeter and the interaction with ADS-B.

GPS Altitude

The Garmin Pilot also displays GPS altitude. During our trips that altitude has differed from the altimeter display by up to almost 300 ft, so this isn't a reliable test to check your altimeter.

The lack of precision of GPS altitude has a scary consequence. 

The Garmin Pilot computes warnings about obstacles and various air spaces using GPS altitude. So when a warning shows a marginal altitude separation, you may actually run into an obstacle or may already be inside forbidden airspace.

Routine Tests

Before every flight, you can do a basic test to check that the TailBeacon is at least operational. While you start the engine and do steps such as turning on radios, do not allow the aircraft to move at all. Once the transponder is operating at the ALT setting, turn on WiFi on the iPad and click to connect with the TailBeacon. Then turn on the TailBeacon app and check that the transponder code and altitude show up.

Once every three months or so, do the following test: When you are near a controlled airport, ask the tower to tell you the transponder altitude, and compare that with your altimeter. Then do the above altimeter test where you use the ADS-B information of other aircraft. 

For a thorough check, do the flight test described earlier and obtain the performance report.

Final Thoughts

Airplane updates are never simple. There are lots of considerations, and only a slow and deliberate process leads to good results.

The age of microelectronics for aviation has begun. It is a smart decision to take advantage of that technology.

The uAvionix company is doing just that. They produce feather-weight electronic equipment for aviation at reasonable cost and thus make a terrific contribution. 

Need Help?

Contact uAvionix for the nearest Qualified Installer. You can also post questions in the comments, and we will respond. 

Have any feedback about the installation of the uAvionix TailBeacon? Please share your thoughts in the comments.

Want to learn more about flying?

  

My book Lessons from Piloting for 45 Years covers close shaves over more than four decades involving thunderstorms, mountain weather, faulty runways, equipment failures, and more.

Learn key strategies for coping with these dangerous situations. They include two tools called Sully's Rule and Forecast Evaluation.