A recent issue of AOPA Pilot carried an article by pilot Gregory N. Brown about an item that may be of interest to deaf pilots concerned about avoiding mid-air collisions. Most collision-avoidance equipment generally costs about $5,000 or more plus installation, but one portable device that costs only $789 is already on the market. It's called the Monroy ATD-200 Air Traffic Detector, and it's a comparative bargain.

It connects to a cigarette lighter receptacle and the pilot's headphone jack. Since no installation is required, pilots who fly multiple airplanes or rent aircraft can readily carry the device from one aircraft to another.

The Monroy ATD-200 Air Traffic Detector listens for transponder transmissions and displays them on a series of LEDs as well as announcing the presence of other aircraft by voice. It lies on top of the glare shield and costs $789.

"The ATD-200 is surprisingly simple to operate, given its capability," the article continued. "Red LEDs depict target distance from your aircraft, the first illuminating when targets approach within approximately four nautical miles. Additional lights go on sequentially as the traffic gets closer, with all five illuminated for targets within 0.5 nm. At approximately three nm, a female voice says, 'traffic,' in the pilot's headset, and at the one nm range she says, 'traffic nearby.' (Monroy has done a nice job with this voice, which is clearly audible but not in itself alarming.) Green LEDs show that the unit is powered and indicate your own transponder reply, while a yellow light identifies Mode S transponder targets (generally Transport-category aircraft)."

The device, the article said, works by interpreting transponder replies from nearby traffic, meaning that aircraft not delivering transponder replies do not generate alerts. This includes not only aircraft without operating transponders, but also those flying in areas without radar interrogations to stimulate transponder replies.

In other words, pilots must still look out the window for traffic.

The ATD-200 does not deliver target bearing or altitude information.. Only the proximity of the target to your aircraft is shown on the LEDs, meaning that when they light up, the pilot must look in all directions to find the traffic.

"The distance to a target is determined by the strength of the target's transponder signal response, based on a 200-watt transponder unit," the article said. "Therefore, if the target's transponder is stronger, the target is perceived as closer. Also, the accuracy of the distance given is plus or minus 20 percent--the closer the target, the more accurate the distance shown on the ATD-200.

"That being said," the article continued, "we've flown with our ATD-200 for more than a year and are delighted with it. Perhaps most surprising has been how much traffic passes nearby that one never sees. Having learned not to panic every time the voice says, 'traffic,' we now search only when LEDs progressively illuminate, or when the lady says, 'traffic nearby.' (Targets illuminating only one or two LEDs are generally too far away to see.)

" . . . Where this unit really shines is in supplementing pilot awareness when one is either distracted or busy--like on long cross-country flights, when operating at uncontrolled airports, shooting practice approaches, flying in marginal VFR weather, or when attention is diverted during flight training, shuffling of charts, or setting the GPS. We cannot always visually identify traffic alerted by the ATD-200, but never when operating the unit have we seen an airplane pass nearby without its first triggering an appropriate traffic warning.

"While anticollision devices like the ATD-200 cannot provide a total safety shield, they do serve admirably as 'extra eyes' in the cockpit to back up your own. Until or unless we can afford something higher up the ladder, neither I nor the three other ATD-200 owners I know would care to fly again without one."

For more information, contact Monroy Aerospace Corp. by telephone at 954/294-9006, or visit the company's Web site (www.monroyaero.com).