Budget Traffic Nags

Improved versions of the Monroy and SureCheck perform better. Monroys ATD-300 enjoys a razor-thin edge.

by Jonathan Spencer

We would like to tell you that there’s been a huge breakthrough in traffic detection technology and that devices selling for less than $1000 work as we’ll as those costing 20 times as much.

We would like to say that there’s no need to spend $20,000 for traffic detection and that one of these nifty little glareshield-mounted boxes is all you need. We would like to say that. Unfortunately, thats not the case.

We last examined these gadgets two years ago and reported our findings in the March, 2002 issue of Aviation Consumer. Since then, both the Monroy ATD-200 and the SureCheck TPAS have been significantly improved or have morphed into entirely new products. And while both work better than the previous versions, neither is the traffic spotter of our dreams. Not yet, anyway. On the other hand, for under $1200-way under, in the case of the Monroy-they do provide an affordable set of electronic eyeballs that will be worth having for some owners.

The Devices
We tested two devices: The Monroy ATD-300 and SureCheck Aviations TrafficScope VRX. The Monroy is an update of the ATD-200 which we examined previously. At $795, its decidedly the less expensive of the two. The TrafficScope VRX is SureChecks follow-on product to their earlier TPAS RX-110. In fact, the two products are too different to describe one as an update of the other. It appeared to us to be more of a clean-sheet product. The TrafficScope VRX sells for $1195. We didnt test another model of the TrafficScope, the VR. Like earlier models of this technology, it sees transponders and calculates range but doesnt track altitude. It retails for $695.

Both the Monroy and SureCheck come with portable antennas that connect to the back of the unit for use on the glareshield. Both can also use an external antenna. The two manufacturers have very different opinions about using an external antenna, however.

SureChecks representative told us they had seen little difference between performance with an external antenna and the portable antenna. Despite that, the SureCheck manual goes into some detail about an external antenna installation, including an option for dual antennas which requires obtaining a splitter from SureCheck.

Monroy told us that they recommend a single external antenna on the bottom of the aircraft and assured us that performance would be considerably better with it. They also note that an unused DME antenna can be pressed into service for this purpose and the unit can also be panel mounted, but it turns out that the installed option is more complex than it first appears.

We tested both of these devices in an airplane equipped with the Garmin GTX330 Mode-S transponder and the Garmin GNS530 for display. The GTX330 provides FAA Traffic Information Service (TIS) for display on the GNS530. The 530 traffic display was our reference, since it reliably shows altitude difference, range, and azimuth for all transponder-equipped targets within a 7.5-mile radius and within 3500 feet above and 3000 feet below, based on ground radar interrogations.

First Impressions
The two devices reflect different packaging and display philosophies. Both are about 5 inches deep and 3 inches wide. The SureCheck, however, is 2 inches high, while the Monroy is only 3/4-inch high. The SureCheck has an LCD display that can be difficult to read in bright sunlight, while the Monroy uses an LED dot-matrix display that is easily read in all light conditions. For night operations, the SureCheck has a backlight and the Monroy has a dim mode.

The compact size of the Monroy seems to have another effect-it gets hot, especially if sunlight adds to its internal heating. In fact, having used both devices at night, we determined that most of the heating of the Monroy comes from sunlight, not the electronics. The manual warns against unreliable operation if it gets too hot to touch (it did) although we werent able to evaluate whether this affected the units performance.

It wasnt clear to us how to use the unit in its recommended position on the glareshield while still protecting it from the sun. A little ingenuity with a piece of white Styrofoam might be called for, but, in our view, it shouldnt be necessary to jury-rig a device for use in its intended location.

The SureCheck has an internal, onboard altitude reference-a simple pressure sensor-while the Monroy does not. SureChecks reasoning is that some Mode-A codes (the four-digit code ATC has you to put into your transponder) produce the same binary code as an altitude code, producing at least confusion and possibly an incorrect altitude for your own aircraft. For some reason, this doesnt seem to be a problem with the signal received from other aircraft. When the SureCheck sees a code from your aircraft that could be confused with an altitude code, it uses its internal altitude reference instead.

When this occurs, a transponder conflict LED illuminates on the SureChecks panel. We found this light to be more alarmist than necessary. SureCheck says that there are many conditions under which the unit will decide that the transponder altitude is unreliable and switch to its internal source. It was lit about half the time during our testing, often for 20 minutes at a time, and then would go out for no apparent reason.

SureCheck further says that for the most part, the pilot can ignore the light. If so, wed like to see a way to dim it; its much brighter than the display and, especially at night, can be annoying for something were supposed to ignore. SureCheck says this light is less intrusive on the latest versions of the unit.

Monroy mentions the Mode-A altitude confusion problem as well, but the ATD-300 simply displays the word IDENT on the display when it sees a questionable code. The manual explains that hitting the transponders ident button will clear the condition.

Of course, ATC may not find your spurious ident amusing, especially if theyve just asked another aircraft to do the same. And when we attempted to clear the condition using the ident button, the fix didnt seem to last more than a few minutes.

Despite both manufacturers assurance that this is a rare condition (SureCheck estimated it occurs 4 percent of the time), we saw it at least a couple of times during two days of testing when we were squawking a discrete code that confused the units. Perhaps Tampas range of codes for VFR Class B traffic are among those that cause a conflict.

Power Source
Both units operate from ships power. The SureCheck, however, is also capable of operating from internal batteries, four AA-cells, which we consider a plus. The batteries make the SureCheck useful in gliders and other aircraft without an electrical system and also ensure that the unit will continue to operate if the ships power fails. For shipss power, both will operate on either 12- or 24-volt systems.

The two units also have a different approach to how they display target range. The SureCheck shows range in tenths of a nautical mile while the Monroy shows range only in nautical miles. We think a range measurement in tenths of a mile is unrealistic, given the mechanism used to make that measurement, which is to judge range by signal amplitude.

While the SureCheck makes some adjustment for transponder power in aircraft they assume are larger-those using Mode-S transponders are considered to be airliners-this is guesswork at best since transponder power can be affected by installation, dirty antennas, aircraft orientation and other unknown factors.

The primary advantage of the SureChecks range display is that you can see a trend sooner. If the range is increasing, you can decide that a target is not a threat and go on to other duties. But don’t expect a target with an indicated range of half a mile to necessarily be half a mile away.

Both units provide an audio output in the form of a female voice that warns of traffic. It actually sounds like the same female voice in both units. Both systems also let you mute the audio. The Monroy mute switch also changes the display to read MSL altitude for any targets rather than relative altitude. Wed like to see a mute option that doesnt change the display.

All the technical mumbo-jumbo aside, how we’ll do they work? The short answer is not as we’ll as you might wish but better than before. Their biggest weakness, at least when using the portable antenna, is spotting traffic ahead and below. This is especially critical if you have an opposite-direction aircraft climbing through your altitude, since this is the traffic conflict with the highest closing speed and shortest available reaction time.

We had a dramatic demonstration of this near Sarasota. While level at 3500 feet, Tampa approach advised us that a 737 was departing Sarasota and would be passing beneath us at 3000 feet. We picked up the 737 quickly on the Garmin TIS and soon had a visual on it. But even when the 737 was we’ll within the 5-mile range of both the Monroy and the SureCheck, neither provided any warning.

In fact, neither provided a warning until the 737 was less than a mile away, much too short a time to find a target and take evasive action. Remember, neither of these units provides azimuth information; we knew where the 737 was because ATC had advised us and we saw it on the TIS display. If we hadnt had these sources of information, we would have had to scan the entire visible horizon to find the traffic, decide if it was a threat, determine the appropriate evasive maneuver and make that maneuver, all in the few seconds the devices gave us.

Later in the tests, we tried both devices with an external antenna. We took Monroys advice and used an unused DME antenna, which was about 30 inches to the right of the transponder antenna. Neither unit performed even as we’ll as they did with the portable antenna. The Monroy kept insisting we had traffic at 0 miles and 0 feet altitude differential and the SureCheck indicated no traffic at all even when we were less than a mile from other airplanes in the pattern and their transponders were showing clearly on the TIS display.

It was clear that our transponder signal was overloading both units. (In our view, they seem to have trouble with Mode-S transponders in the host airplane but they might do better in Mode-C equipped airplanes.)

Next, we tried turning our transponder off briefly. This removes the local altitude reference for the Monroy, but the SureCheck has its internal reference. Nevertheless, neither unit indicated any traffic with the external antenna.

We were unable to explore this further because of time limitations. Its possible there was a problem with the antenna -one of SureChecks representatives said that DME antennas don’t usually work we’ll with these units, contradicting Monroys advice. Simply hooking up an unused DME antenna might not be a quick solution. And if it takes several hours of tech time just to find the right location for a new antenna installation, the concept of a cheap traffic unit begins to erode.

False Security
Although neither Monroy nor SureCheck overstate the capability of these devices in their promotional material, our biggest concern with the inexpensive traffic nags is that they will lull pilots into relying on them in lieu of a normal visual scan. If the unit on your glareshield points out traffic, you’ll generally look for it. Unfortunately, it may be pointing out a target 3 miles away flying away from you while there’s a target ahead and below aimed straight at you that the box isn’t seeing yet.

Since most people who buy these units wont have a TIS display, as we did, theyll rarely know which targets the devices are not finding unless they have a near-miss or get a traffic callout from ATC and notice that the traffic unit didnt warn them in advance.

Our other concern is that traffic monitors can create their own unique class of problem. Watching the range of a target slowly count down and being unable to find it can make you do things you wouldnt do otherwise, such as make a sudden altitude or heading change. Such an action could cause an accident that otherwise wouldnt have occurred.

Once you understand the weaknesses of this technology, however, you can compensate. For example, if you know that its fairly reliable in seeing airplanes at altitudes at and above your own, you can spend more head-up time looking for targets below your altitude. And you can discipline yourself not to make sudden altitude or heading changes unless you see the traffic.

After flying both units in direct sunlight, cloudy conditions and at night, we decided we like the Monroy display better. Its easier to read both in daylight and in darkness. True, it doesnt have as much information as the SureCheck, but we wonder whether all the details in the SureCheck are as useful as the basic information of traffic distance and altitude.

The SureChecks local altimetry source is a definite plus. If the Monroy has a problem with your transponder code, it simply displays IDENT and doesnt display any traffic. The SureCheck switches to its internal altimetry source and keeps on working, simply lighting the transponder conflict light to tell you what its doing. We found that its internal source agreed quite we’ll (usually within 100 feet) with our altitude encoder.

Here are some other features worth mentioning:

Ground, Flight, Auto modes-The SureCheck allows you to select Ground mode, which restricts it to looking only above your current altitude, or auto mode, which starts in ground mode and changes to flight (normal) mode when it detects a 200-foot altitude increase.

Own altitude -The SureCheck has a button to display the altitude your transponder is sending to ATC. The Monroy will automatically display this when no traffic is in view.

High or low voltage warning-The Monroy displays HI VOLT or LOW VOLT whenever it detects these conditions. It also provides a voice warning. When your transponder is turned off, the Monroy displays your bus voltage.Altitude alert-The SureCheck warns when your altitude changes more than a set amount. You can set the warning to go off at 200 feet, 500 feet, or 1000 feet.

For the price-$800 to $1200 depending on which unit you select-the portables strike us as cheap insurance against a mid-air collision or near miss.

But you get what you pay for. don’t expect either unit to find all the traffic. Both will miss lots of targets, especially those ahead and below the aircraft. And once you start installing one of these in a panel using an external antenna, you could nearly double the cost.

In adding all these numbers up, refer to the chart on page 6 which compares prices on all the current offerings across all price ranges. With the Garmin Mode-S based TIS available for about $5000, owners will need to put a sharp pencil on the decision to go down market with a portable. But the $5000 applies only if you already have a GNS430 or 530 in the panel. And maybe you don’t want to spend that much on traffic gear and the portable suits your needs.

Which is best? Both are improved over previous models and we don’t think you’ll go wrong with either, keeping in mind that this technology has sharp limitations. We give a razor-thin edge to the Monroy ATD-300. Its $400 cheaper than the SureCheck, has a lower profile on the panel and a simpler, easier-to-read display.

Our impression is that the ATD-300 more often saw traffic that the SureCheck missed but, to be fair, the performance of both units is strongly influenced by antenna position. For the extra $400, the SureCheck gives you the ability to run on batteries and has the onboard altitude sensor, neither of which the Monroy has.

As noted, this allows the SureCheck to make relative altitude determinations when the host aircraft Mode-C isn’t available, which appears to be the case about 20 percent of the time for reasons that arent clear.

If that capability is important to you or you cant run on ships power alone, the SureCheck TrafficScope is the better choice, in our view. In any case, we think SureCheck deserves kudos for dramatically improving its product over the previous iteration and we give the company high marks for much improved customer and technical support.

Also With This Article
“Traffic Avoidance Market Scan”
“Prox Alert: Missing in Action”

• Bendix/King, 877-712-2386, www.bendixking.com
• Garmin International, 800-800-1020, www.garmin.com
• Goodrich/L3, 616-949-6600, www.as.l-3com.com
• Monroy Aerospace, 954-294-9006, www.monroyaero.com
• ProxAlert, www.proxalert.com
• Ryan International, 800-877-0048, www.ryaninternational.com
• SureCheck Aviation, 888-340-8055, www.surecheckaviation.com

-Jonathan Spencer is an Aviation Consumer contributing editor. He bases his Cardinal near Boston.