Turbine Pilot

The Stormscope inventor turns to collision avoidance

TCAS is proving to be a very good answer to a difficult problem: how to give aircraft pilots and crewmembers some help in the cockpit in detecting potential collisions with other aircraft. Trouble is, the price and, to a lesser extent, the size and weight of TCAS equipment put it out of reach of most general aviation aircraft. Enter TCAD, or traffic and collision alert device, a relatively inexpensive and compact piece of electronics that, like TCAS, listens to and analyzes the language of air traffic: transponder signals.

TCAD is made for general aviation aircraft. It comes in three versions, two panel-mount units and one with a smaller panel display and remote-mounted receiver-processor. The panel-mount ATS-8000 sells for $7,700; the ATS-7000, which lists for $4,975, is identical to the 8000 except that it lacks some basic features; the remote-mounted ATS-9000 lists for $11,250. TCADs have been installed in every type of aircraft from homebuilt to Boeing 737.

Columbus, Ohio-based Ryan International developed, manufactures, and sells the TCAD. Company President Paul Ryan has already made a huge contribution to general aviation safety as the inventor of the Stormscope. Ryan's innovative ideas spring from personal experience as a pilot. The Stormscope was the ultimate result of his inadvertent encounter with a thunderstorm; close encounters with other airplanes led to the TCAD.

TCAD is in the same conceptual ballpark as TCAS but with some important differences. TCAD is a passive device. It listens for UHF signals transmitted by an aircraft transponder and, based on its analysis of the signal, displays the altitude and distance of the nearby aircraft. Mode A-only signals yield distance information but no altitude. Other TCAD features (except on the 7000) include an altitude alerter and density altitude calculator.

TCAD does not know nor display the direction the signal is coming from. The lack of traffic bearing information is an inherent limitation of the device but one that makes possible the TCAD's rock-bottom price compared to a minimum of about $60,000 for a TCAS system.

Ryan argues, with justification, that knowing the bearing isn't absolutely vital as long as altitude and distance are displayed. TCAD's worth is based on the principle that as long as at least some altitude separates two aircraft, a midair collision between the two is impossible. If the TCAD display shows that another aircraft is closing and its altitude is either converging or the same as yours, take evasive action. Climb if the other aircraft is climbing into your altitude, descend if it is descending, or take your choice if it is level and at your altitude.

With experience, a TCAD user also acquires a knack for spotting traffic quickly. That's because the unit provides information, particularly relative altitude, that's helpful in targeting the visual search.

The way to visualize the TCAD concept is to imagine a three- dimensional disk or volume of airspace — Ryan refers to it as a shield — with your airplane in the center. A small disk is in effect when flying in terminal areas, a larger one for outside terminal areas, and a larger disk still for enroute cruising. You set the exact boundaries of the disk using the buttons on the face of the TCAD unit. For example, the terminal shield might be set at a radius of 1 nautical mile and an altitude of 500 feet above and below, the standard shield at 2-nm radius and 1,000 feet, and enroute at 5 nm and 2,000 feet. Buttons on the face of the unit correspond to Terminal, Standard, and Enroute shields. Select whichever is appropriate for the phase of flight. The unit also has a Ground mode that displays transponder-equipped aircraft 100 feet or higher above your aircraft. (The 7000 has one fixed-size shield only.)

The TCAD unit processes any and all transponder signals it detects. When it determines that a signal from an aircraft originates from within the selected disk or shield, it displays the intruding aircraft's range and relative altitude and issues an electronic tone. Small directional triangles indicate whether the aircraft is climbing or descending. On the 8000 and 9000 model, the actual altitude and transponder code of the threat aircraft are displayed with the touch of a button. The more sophisticated models also can show secondary and tertiary threats; the ATS-7000 shows only the primary threat.

Knowing the subtleties in the displayed information is helpful in constructing a more complete picture of where a potential threat aircraft is and where it is going. For example, if the range display chatters — fluctuates back and forth quickly between two distance figures — you can be pretty sure the threat aircraft isn't closing but is on a crossing course to yours. That's because transponder signals fan out from the transmitting antenna not in a perfect circle, but in irregular lobes. These lobes are read by the TCAD antenna and lead to the fluctuating range determination. If, however, the displayed distance to the threat aircraft decreases uniformly, better make sure there is adequate altitude separation.

AOPA's Beech A36 Bonanza has been equipped with a Ryan TCAD ATS- 8000 for some time. It took some getting used to — remembering to update the barometric pressure and progress from terminal to standard to enroute modes.

Also, at first I found the tones alerting me to a potential threat to be intrusive, especially in busy terminal areas where I concentrate heavily on flying the airplane and looking for traffic. I tuned out the tones. It was an ironic reaction because the terminal area is where TCAD is needed most — that is where most midair collisions occur.

My early reservations about TCAD have disappeared. I have assimilated it into my cockpit workflow, scan, and thought process.

The TCAD is the only altitude alert device on the Bonanza, and I use it for that function on every flight. I also appreciate and use the density altitude calculator.

Most of all, I have come to rely on its basic function, which is to alert me to potential collision threats. I'm confident in its ability to detect other transponder-equipped aircraft. Based on my visual observations of displayed threat aircraft, the altitude readout is very accurate. Range is less so. TCAD determines range based on the amplitude of the signal received from a typical general aviation transponder. More powerful transponders make TCAD think the aircraft is closer than it really is, but that's okay. More powerful transponders are used in larger, faster aircraft so an early warning of a potential threat is good.

TCAD's usefulness doesn't mean you should put all your collision avoidance marbles in it. That would be foolish because not every aircraft is equipped with a Mode C transponder. Ryan makes the point that pilots using TCAD must continue to practice see and avoid, listen to other pilots on the frequency, and use ATC radar to ensure separation.

I can't say that TCAD alone has saved my bacon yet, but it has made me more aware of the amount, proximity, and location of traffic. I'm a more vigilant pilot because of it, and I think a safer pilot.