September 20, 1998 The Ryan TCAD: Collision Avoidance on a Budget

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by	Carl Marbach

About the Author ... Carl Marbach is a co-founder of AVweb and its Publisher. Carl is a 4,000-hour pilot, and commutes between homes in Boca Raton, Florida, and Aspen, Colorado, in his 1978 Aerostar 601P. Carl was the founder and CEO of Professional Press which published five computer magazines including DEC Professional. After Professional Press was acquired by a venture capital firm, Carl founded Internetwork Publishing Corporation and now devotes himself to the emerging field of electronic publishing via the Internet. A lifelong resident of Philadelphia until 1994, Carl and his wife Helen now live in Boca Raton, Florida.

A mid-air collision can, as they say, ruin your day. While we all know that we should spend lots of time and effort looking outside for other aircraft, the increasing computerization of our cockpits — GPSs, FMSs, digital engine analyzers, and other bleeding-edge cockpit gadgetry — is demanding ever more of our time inside. A United Airlines check pilot once expressed his airline's concern about the new flight management systems and "glass cockpit" aircraft this way: "If you looked in through the windshield of a modern jetliner, all you'd see is two bald spots." Those, of course, would be the heads of the front seat occupants looking down at their FMS computers instead of looking outside.

To answer some of those concerns, airlines have had to install TCAS — Traffic Collision Alert Systems — in all their aircraft. Bizjets have followed suit and most modern jet aircraft are so equipped today. But, as often happens in aviation, those who need it the most don't have it. General Aviation operates in a more crowded environment than the airlines, and to make matters worse, we do it mostly VFR. There are about 5,000 airline aircraft flying today, but more than 200,000 GA planes in that same airspace. The airlines fly most of their trips at the Flight Levels above 18,000 feet while GA spends most of its time below 8,000 feet in the haze, smog, rain and other challenges to visibility.

When I invite non-pilot passengers aboard my Aerostar, most look at the instrument panel and are comforted by the prominent radar in the center, because they think it is used to avoid other aircraft. When they see a "Radar Equipped" decal on the side of an aircraft, the general public thinks it is for traffic avoidance rather, not weather avoidance. Most folks would be horrified to learn that our only tool for avoiding collision is looking out the window.

So why not some type of collision avoidance system for GA? Well, the TCAS system that the airlines and corporate jet-setters use is simply way too expensive. One bizjet operator told me that the TCAS installations in their airplanes cost more than $75,000 each. Recently, BF Goodrich developed a lower-cost GA system, very similar to TCAS, that sells for about half of that figure, but that's still far beyond what most piston GA aircraft owners can afford.

The lowest-cost collision avoidance solution presently approved for certificated aircraft comes from Ryan International Corporation in Columbus, Ohio. Inventor Paul Ryan is perhaps best known for developing the Ryan Stormscope thunderstorm avoidance system, which was later acquired by 3M and later by BF Goodrich. Ryan's solution for the GA collision avoidance problem is called TCAD — Traffic Collision Avoidance Device — and has now evolved into a family of five models with prices that range from $4,995 to $13,850 (not including antennas and installation). A few months ago, I had a top-of-the-line Ryan TCAD 9900B installed in my 1979 Aerostar 601P, N6069N.

A Different Approach

The Ryan TCAD system is different than TCAS, which is why the names differ slightly. The TCAD is a passive device, which listens to transponders, some of which may be a collision threat, while TCAS is an active device that actually interrogates transponders in the vicinity. Consequently, the TCAD is effective only if nearby transponders are being interrogated by something else, like an ATC radar facility or a TCAS-equipped aircraft. This doesn't seem to be a problem, however, at least in the conterminous U.S. I've now flown with TCAD in some very remote areas of the "Lower 48" and it is a rare event indeed when my transponder reply light isn't blinking. (If the transponder is blinking, it's being interrogated from somewhere, and the TCAD will be effective.)

Display unit, TCAD 9900 B.

The method of traffic display used by the Ryan TCAD is also very different from TCAS. TCAS typically displays the position of threat traffic in graphic fashion on a circular instrument showing your airplane in the middle, and some TCAS systems can display traffic on a mapping system or EFIS display. In contrast, the Ryan TCAD has only an alphanumeric display that shows the altitude and approximate distance of the threat — and, on my top-of-the-line 9900B model, an arrow showing the approximate direction of the threat.

The alphanumeric TCAD display takes some interpretation, and since the traffic may be closing rapidly the non-intuitive nature of the display can be a problem. Fortunately, after flying with the TCAD for a while, you learn how to determine quickly if the traffic is a real threat (i.e. is at the same altitude and close by) and what direction to look for it. My experience with the TCAD is that when it shows no threats you can relax, and when it reports traffic, you better get your eyes out of the cockpit and start looking.

Like all good tools, it takes a little while to learn to use this one quickly and easily. But, by my second or third flight after installing TCAD, I found that interpretation took less effort, and I learned how to assess whether a warning was something to worry about or not.

Ryan has recently announced the ability to display traffic from some TCAD models on Eventide's ARGUS moving-map displays. Since I have an ARGUS installed in my Aerostar, I'm looking forward to that enhancement.

Installation is No Picnic

TCAD 9900 B processor in nose avionics bay.

Installation of the TCAD turns out to be a non-trivial event, especially if you're installing the advanced 9900B model. That system consists of a remote-mounted processor, a transponder coupler that attaches to your transponder (the TCAD needs to suppress your transponder periodically so that it can hear the transponder replies of other aircraft), a panel-mounted indicator, two antennas (bottom and top), an optional visual traffic warning light, and an optional connection to the aircraft's audio system. The TCAD 8800-series does not require the remote mounted processor, but still needs all the other stuff. As you can imagine, installing all this takes considerable time and effort.

And then, of course, there's the Friendly Aviation Agency...

Bottom antenna installation, TCAD 9900 B.

My Aerostar 601P is a pressurized aircraft, and the local Flight Standards District Office (FSDO) here in Fort Lauderdale, Florida, insisted that a Designated Engineering Representative (DER) inspect the aircraft, design the antenna installation, and create engineering drawings to indicate where each rivet and mounting screw should go before they'd let my avionics shop drill the first hole in the aircraft skin. The FSDO also required that the radio shop create a wiring diagram and installation plan, and get that whole package approved by an FAA avionics inspector before starting installation. As a result, I was out-of-pocket for $1,000 before the first hole was drilled or screw was turned!

I have heard that certain other FSDOs are not so difficult and demanding, and perhaps in retrospect I would have been better off going "FSDO shopping" and taking the airplane somewhere where the local Feds wouldn't make a Federal case out of a simple avionics installation. It wasn't very long ago that radio shops could install antennas on my airplane without any of this costly and time-consuming rigmarole. And, for what? What airplane accident has ever been caused by the antenna installation? Well anyway, I can tell you that here in South Florida, the FAA is more unfriendly to GA then ever before, and they made us dot every i, cross every t, and jump through every hoop they could come up with. (This will be the subject of a future article.)

TCAD display installation in my Aerostar. The location is less than optimal.

There is a lot of wire to be run for the Ryan TCAD 9900B connecting the two antennas and the panel-mounted indicator to the remote-mounted processor. The processor is mounted with other remote avionics, generally in a nose or tailcone avionics bay or on the firewall, while the indicator unit is mounted somewhere in your crowded panel. The 9900 indicator is 3.26 inches wide and 1.5 inches high and it about 9 inches deep, making it easy to find panel real estate, but hard to find a spot that provides adequate depth behind the panel. My panel is so tight that the only place I could find to mount the TCAD display was on the center console aft of the throttle quadrant — certainly not the ideal location because it requires that I look down to read the alphanumeric display.

The processor and display are cabled to each other, to the transponder, and to the top- and bottom-mounted antennas. Both antennas are required to ensure that your airplane structure won't blind the avoidance system. The 9900B uses different (directional) antennas than any of the other TCAD models because the 9900B has to resolve the direction of the threat. In order to do this, the 9900B uses more sophisticated (and expensive!) antennas and two additional receivers in the remote mounted box.

TCAD 8800-series display/processor.

The new, lower-cost 8800-series TCAD is all contained in one panel-mounted box, simplifying the installation a bit, but it still requires two antennas. The panel-mounted box is standard width, so if you have some radio room left it will fit nicely in your radio stack.

Installation involved fabricating a second avionics shelf.

When all was said and done, total installation time for my plane was about 125 hours. (That's more than three man-weeks!) According to Ryan International, they expect between 50 and 100 hours to be more typical. There were several reasons that my installation took longer than most. To begin with, Aerostars are tight and hard to work on. In addition, the avionics shelf in my Aerostar was full and so the shop had to fabricate a second one. Finally, there was all the nonsense with my local FSDO, which I would guess added about 25 hours of extra work, plus the DER charges. Hopefully not all FSDOs are this demanding.

The TCAD is STCd for the Cessna 414 and most installations on other airplanes are done referencing that STC. I would also guess that the second Aerostar in this neighborhood to have a TCAD installed would benefit from the experience the FAA had with mine and the installers could use some of the drawings and things again. All of this adds up. It costs to be first.

Choosing Among the TCAD Models

There are five separate TCAD models available, two self-contained 8800s, and three remote-mounting 9900s. Ryan offers a complex matrix that compares the features of each model but to my way of thinking, it's actually pretty simple to decide which model to buy.

The first thing you have to decide is whether to buy an 8800-series or a 9900-series. The 8800-series is much less expensive, but cannot be upgraded to provide direction-of-threat information. If you can live without that little arrow, my suggestion would be to purchase the most basic TCAD (the 8800 Silver model, $4,995) and save yourself about nine grand.

The TCAD 8800 Silver gives you the basic traffic warning information you need: the altitude of the threat aircraft relative to your own (e.g., 100 feet above, 700 feet below), and the approximate distance. For a thousand bucks more ($5,995), the 8800 Gold adds a transponder code readout and a few other goodies, but nothing you can't live without. Besides, the lower-priced Silver model is easily upgradable to the Gold if you so desire.

The most basic of the TCAD 9900-series lists for $7,995 and offers similar capabilities to the 8800 Gold but in a remote-mounting package. The 9900A goes for $9,995 and provides customized "shield size" (discussed later) plus a pleasant female voice that advises you of "Traffic" rather than just a beep. Finally, the top-of-the-line 9900B costs $13,850 and is the only TCAD model that provides direction-of-threat information. Once again, any of the lesser 9900-series units can be upgraded to a 9900B.

Frankly, it seems to me that there are really only two TCAD models worth considering. If you can't justify the cost of the direction-sensing 9900B ($13,850), I'd suggest going with the low-end 8800 Silver ($4,995). To my way of thinking, the in-between models don't seem to offer the added functionality that their incremental price commands. To make a long story short, 8800 Silver gives you basic alerting with the threat's altitude and approximate distance, and the 9900B adds direction-of-threat information and the ability to display threats on an ARGUS moving map display if you have one. Your choice.

Flying With The TCAD

The TCAD installed in my Aerostar is the 9900B which has all the bells and whistles. Its panel-mounted indicator has a main screen and a secondary side screen, both of which comprise 20 LED cells to tell you what's going on.

The TCAD defines a "shield size" which it uses to determine when it should alert you to traffic. When traffic enters your shield a tone sounds and the display tells you about the "intruder." The 8800-series and the basic 9900 alert you with a tone, while the 9900A and the 9000B have a female voice that says, "Traffic." The 9900A and the 9900B TCAD defines three shields for you that can be modified by the user, while the 9900 has one fixed shield size (the Enroute shield). The Enroute shield is plus or minus 2,000 feet and 3.0 iNM.

"iNM" denotes Indicated Nautical Miles, and is the TCAD's best guess on how far away the traffic is, based on the strength of the received transponder reply. This guess will be most correct for general aviation transponders, but will show airliners (which use higher-power transponders) to be closer than they really are. The Standard shield is plus or minus 1000 feet and 2.0 iNM, and the Terminal shield is plus or minus 500 feet and 1.0 iNM. The 8800s have either 3 or 4 different fixed-size shields.

When the TCAD is powered up, it enters Ground Mode. To avoid nuisance indications from taxiing aircraft and other ground traffic, Ground Mode limits its range to 1.0 iNM and a height of 1000 feet above you (presumably there will be no aircraft below you). In addition traffic at and below 100 feet above you will not be displayed. Approach Mode is similar to Ground Mode in that the TCAD eliminates warnings from aircraft on the ground. You must enter the elevation of the airport you are approaching for the TCAD to use Approach Mode.

The more expensive TCAD systems allow you to set custom shield parameters if you want to. In my flying, I have not found it necessary to modify the factory settings, but I do use different shields for different segments of the flight. In some busy terminal areas, if you use the Enroute shield, the TCAD will point out too many targets; using the Terminal shield reduces the number of targets to a more manageable number.

When the TCAD is searching for traffic, but not finding any within your chosen shield, the 8800 Gold and the all of the 9900-series units show your current altitude and indicates that it is searching. The screen on the right will show if you have selected the altitude alert feature. The altitude alert feature allows you to set a desired altitude you are climbing or descending to. When you reach 500 feet away from this target altitude, a tone will sound. After you are level at this target altitude, the tone will sound again when you deviate from this by 200 feet. When the altitude alert function is enabled, a small "a" is displayed on the right side display. While not quite as good as a good altitude alerter system, this TCAD feature is useful. I would prefer a slightly more penetrating tone for altitude deviations, but otherwise it is a worthwhile feature.

Collision Avoidance

Paul Ryan's philosophy of collision avoidance is simple: aircraft cannot collide if they are at different altitudes. Using this principle, you should either see the traffic, or make sure you are at a different altitude than the threat aircraft is. All of the Ryan TCAD models — even the lowest-cost one — display the altitude difference between you and the threat to be certain that you will not have a collision, on the theory that altitude separation is the only sure way. Since the TCAD is reading pressure altitude from both the threat's altitude encoder and your own, the altitude differential shown on the display is independent of any altimeter setting you or the threat may have entered. It does assume that both encoders are working correctly and calibrated accurately. An indicator on the TCAD display tells you whether your altitude separation in getting larger or smaller.

Ryan suggests that if you have a threat that is getting closer and your altitudes are the same, then you should climb or descend to eliminate the chance of a collision. If my TCAD shows that a threat is at my altitude and the indicated distance is getting smaller, I start to worry. Unless I can spot the intruder, I will change altitude by 100 or 200 feet to eliminate the possibility that the traffic is overtaking me from behind or is somewhere else I can't see.

All pilots know that they are much less likely to have a midair collision if they are actively looking outside for traffic. The best thing about the TCAD is that it reminds you to look outside, and tells you when you should be looking in earnest. Like most of the traffic pointed out by ATC, you are not likely to see all of the threats the TCAD tells you about. This does not mean that the TCAD is reporting traffic that doesn't exist, it just means you didn't see them because they were behind you, obscured by the haze or whatever. If they had been in front of you, or on a near collision course at your altitude, and you were looking hard, I believe that the TCAD would give you a good chance of seeing and avoiding that traffic.

How high?
How far?
What direction?	(9900 B only)

All TCAD models receive, decode and display traffic from transponder replies within your shield. All models report the threat's relative altitude and approximate distance. The 9900B uses two extra receivers and a more complex antenna system to resolve the direction of the threat, and displays this information by means of an arrow on the display that points to the threat in 45-degree increments.

When a threat enters your shield the alert tone or voice sounds, an annunciator light is lit and the panel mounted unit displays the intruder's altitude difference from you and his indicated distance. Next to the altitude difference is an indicator telling you if the altitude difference is increasing or decreasing. The display provides a variety of useful symbols that help you assess the threat environment.

When traffic gets within 500 feet vertically and within 1.0 iNM, the TCAD generates a repetitive beep to get your attention. The beeps increase in frequency if the traffic gets within 300 feet and 0.7 iNM. By this time, your head is really on a swivel as you scan for traffic.

Some Experiences Flying With TCAD

Ideally, the TCAD display should be mounted in a position that makes it easy for you to shift your eyes between the display and your outside traffic scan. Unfortunately, that was not possible in the limited space available in my Aerostar's crowded panel. The TCAD wound up being installed on the center console, where I have to look down to see it.

The good news is that even with this poor positioning, I found that with some practice I can look at the TCAD and very quickly look back outside. If you know what you are looking for on the TCAD display, only a very brief glance at the readout is required. When traffic enters my shield, an annunciator light mounted directly in front of me and at eye level lights, a female voice calls "traffic," and a tone sounds. I then quickly glance down to the TCAD, absorb the information on altitude, distance and direction and then look outside to see if I can see the threat.

Usually I can find the target visually. Flying over the Everglades into my home base of BCT (Boca Raton, Florida), for example, I heard a King Air call in on Unicom also reporting west of the airport. There were two of us, converging on BCT, both at about the same speed. Even if we were separated now, we would get closer together as we approached the airport. The TCAD registered a threat, pointed 45 degrees to the right of the nose, and indicated the traffic was 2.5 miles away and 200 feet below me. Bingo! There it was. From here it was easy to fall in behind (even though everyone knows Aerostars are faster than King Airs!) and follow him into the pattern. Neat, easy and safe.

Another flight from PWM (Portland, Maine) to N71 (Mt. Joy, Pennsylvania) took me west of Boston. The weather in my vicinity had just cleared from a frontal passage, but BOS was still low enough IFR that they were holding airplanes all around the area waiting their turn for the approach. As we flew about 35 miles west of the coast, the TCAD faithfully pointed out all the holding aircraft as they circled the intersections surrounding the area. Boston was so busy that VFR advisories would have been out of the question, and fortunately for me, I had my own little box telling me where the potential traffic was.

Continuing on to N71, I entered the pattern with the knowledge that I was the only plane in that pattern because the TCAD was silent. The TCAD can be as helpful quiet as it can be when active. Remember that it is a "big sky" out there and that most of the time the TCAD will be silent. I believe it was Burt Rutan that said, "Next time someone tells you about the crowded sky, tell them to go outside and look up!" The proof of this is that the TCAD is silent most of your flying time which adds enjoyment to the flight. When it wakes up and announces "traffic," it's time to start looking hard.

When entering a busy terminal area, the TCAD can become too busy. The processor is capable of showing three threats at once and tracking more than 50 threats, determining which three are the most critical and displaying them. Although it requires some button pushing to see more than the threat it considers the most serious, with practice you can manage to keep track of the secondary and tertiary threats as well. When there are too many threats, switching the shield from Enroute to Terminal usually solves the overload problem.

Flying from Denver, Colorado, to Las Vegas, Nevada, over some of the more uninhabited part of the U.S., the TCAD was mostly silent. The 9900 A&B have an "Unlimited" setting which sets the shield size to plus or minus 10,000 feet and 6 iNM. Using this setting finds traffic that is definitely no factor but helps to break some of the monotony of just cruising over the desert. Using the "identification" feature (available in all but the lowest-cost 8800 Silver model) allows you to see the transponder code the threat is squawking, or the tail number if the traffic has a Mode S transponder (as all TCAS-equipped aircraft do). It isn't unusual to see N970AA cruising 9,000 feet above you — this would be some American Airlines jet — which wouldn't show on any shield size except "Unlimited." During these low traffic quiet times, the TCAD can serve its purpose the best — there's no traffic to worry about. Here when we are most complacent is when we are ripe for trouble. The TCAD's ability to "wake us up" is one of its most valuable attributes. In the '50s, it was a mid-air collision of two airliners over the sparsely populated Grand Canyon the spurred the radar-based ATC system we have today. We all know we have to be vigilant in busy terminal areas, but at some time during most flights we kick back and relax a little. The TCAD could bring you back to full attention if a threat enters your shield.

I use the altitude alert feature to remind me of where I am climbing or descending to should I forget. As a bonus, it also shows the altitude you are sending to ATC from your own altitude encoder. In one case, it alerted me to a problem when my encoder became intermittent — instead of the aircraft's altitude, the TCAD display showed only asterisks.

I recently spent a lot of time flying a friend's Cessna 340 that did not have a TCAD aboard and I found that I missed its friendly "traffic" alerts. The TCAD adds a lot of relaxation to a flight when there are no alerts showing. I realized while flying the 340 that traffic was possible at any time. This doesn't imply that it is impossible for traffic to enter your shield without the TCAD responding. That could happen if there is a fault in the intruder's transponder or encoder, there are no ATC facilities nearby to interrogate the other transponder, or there could be a malfunction in the TCAD itself. But, when the TCAD is quiet, it is certainly less likely that there is a collision threat nearby.

I Like The TCAD, But...

The bottom line here unfortunately is the bottom line. The TCAD is undeniably expensive. Even the least-expensive 8800 Silver (at $5,000) is not exactly cheap, and in an era of $500 handheld GPSs, it seems like a lot of dough for what ought to be a fairly simple box. Add $750 for installation and another $750 for antennas, and even the least-expensive TCAD installation will set you back almost $7,000.

On the other hand, the price is in line with some of the newer multifunction GPS navigation units being introduced. The TCAD is definitely leading-edge electronics for your plane, and is priced accordingly. The top-of-the-line 9900B lists for $13,995 (also not including antennas) and will cost about $1,000 to install. Nobody ever said airplanes were cheap. The TCAD adds to this expense burden, but without a doubt also adds a level of confidence and safety that surely enhances the value of your airplane and the experience of flying it.

The TCAD is clearly not a required piece for your panel. But neither is that second ILS, radar altimeter, altitude alerter, fancy clock/timer, ANR headset, stereo music system and lots of other stuff that make your job easier and the flying safer and more pleasant. The Ryan TCAD adds some serious functionality to your airplane.

When I buy scuba diving equipment (which ain't exactly cheap, either), my wife always asks if what I am buying involves breathing. When I say yes, she says, "buy it." When you go to write the check for the Ryan TCAD, ask yourself if it involves avoiding midair collisions. If it will help keep you and other flying machines from running into each other, you might just say, "buy it."