Avionics: Traffic Tools

Seeing what the airliners see--for a price

November 1, 2008

Since its initial deployment in the early 1990s, the radar-based Traffic Alert and Collision Avoidance System (TCAS) has enjoyed great success in reducing midair collisions and now equips more than 25,000 aircraft worldwide.

These devices are fairly large, robust and expensive, however, and their use has been limited to airliners and large business jets.

Consider Honeywell’s CAS 67A, a good example of a modern, airline-qualified TCAS II. It comes with a computer processor, a Mode S transponder, a pair of cockpit displays, a controller head, and one or two antennas. The hardware alone lists for around $130,000, and weighs more than 30 pounds.

A level of TCAS-like capability is migrating downward, however, and recent product offerings are well within the grasp of most piston aircraft operators. Generally, these devices fall into two basic categories: active sensors that emit their own interrogation pulses and process other airplanes’ transponder replies, and passive units that use Mode S transponders to monitor other airplanes’ interrogations and replies.

In addition, the FAA’s Traffic Information Service (TIS) is still available; this takes traffic information from participating ATC radar facilities and presents it on a cockpit display, just like datalink weather. As TIS is geographically based, and subject to line-of-sight interference—as well as the time lag associated with data transfer—it is better suited to strategic planning than for dodging other airplanes in real time.

Automatic Dependent Surveillance-Broadcast (ADS-B) technology is coming to the U.S. national airspace system, and its use as a collision avoidance tool seems assured. Plans are already in the works to show ADS-B data on TCAS displays. Still, no equipment mandate is expected to take effect until 2020 at the earliest, and the U.S. government has yet to decide which form of ADS-B transceiver hardware—1090 MHz or Universal Access Transceiver (UAT)—will become the standard.

For now, active collision avoidance (commonly referred to as Traffic Advisory Systems) can be considered the top of the line for GA users. Although specific features differ, these products work by interrogating “threat” aircraft transponders for a reply, which is then conveyed to the pilot through a set of standardized visual and aural alerts.

This first alerting level—OT for Other Traffic—appears as an open diamond shape, with the altitude separation between the host and threat aircraft indicated and an arrow showing if the threat aircraft is climbing, descending, or maintaining altitude. OT is not considered an immediate threat, although it is within range of the TAS unit.

Proximity Alert (PA), the second level of TAS alerting, signifies a potential traffic conflict ahead. It’s displayed with the same data as OT; only now the diamond is solid, not open. Typically, both the OT and PA alerts are shown in cyan on color displays, and in white on monochromatic (black and white) displays.

In the final, most urgent level of alerting, a threat appears onscreen as a Traffic Alert (TA), denoted by a yellow circle and an automated voice warning, “Traffic! Traffic!” TAs are triggered when other aircraft cross a certain distance and closure rate thresholds; the goal is to give pilots at least 30 seconds warning at a closure rate of up to 1,200 knots—a realistic scenario where jets are concerned.

If the threat aircraft is higher, its relative altitude appears with a plus sign above the target depiction (+03 = 300 feet above). If it’s lower, a minus sign appears instead. If the target aircraft is climbing or descending at 500 feet per minute or greater, a direction arrow appears next to the symbol to denote its movement trend.

Old friends, new names

A trio of avionics vendors supports the TAS market: Avidyne, Bendix/King, and L-3 Communications Avionics Systems. Prices range from just under $10,000 for products earmarked for the piston single market to more than $25,000 for systems oriented toward turboprops and light jets. Price is largely a function of performance, with key criteria including horizontal and vertical range, and service ceiling.

Avidyne is offering its TAS600 family, with its top-end TAS620 virtually identical to the Ryan 9900BX it acquired with its November 2005 buyout of Ryan International. Priced at $20,990, the TAS620 has a range of 21 nautical miles, and a 9,900-foot maximum vertical separation, and is rated to 55,000 feet. Avidyne recommends this system for high-performance fixed-wing aircraft, and helicopters.

Next in line is the TAS610 ($14,990), for mid-performance fixed-wing airplanes and rotorcraft. This unit offers 12-nm range, a 3,500-foot vertical range, and a 25,000-foot ceiling. The entry-level TAS600, aimed at single-engine piston aircraft, is the least expensive of all TAS offerings. For $9,990, operators get seven-nm range, a 3,500 vertical range and an 18,500-foot ceiling. All three Avidyne TAS units employ dual (top and bottom) transponder-type antennas, are able to display up to nine individual targets, and come with a two-year warranty.

Bendix/King’s KTA 870 ($26,773) is a module-style unit compatible with most multifunction displays. It has a display range of up to 40 nm, an 8,700-foot vertical range, and a 51,500-foot ceiling. The KTA 870 uses two antennas—one on the top of the aircraft and one on the bottom—to help keep the aircraft from blocking its own signals.

Users have a degree of control over the KTA 870 coverage area. On takeoff, they can select the “above” view, which displays traffic 8,700 feet above and 2,700 feet below. On approach, users are advised to select “below”; this focuses the system on traffic 2,700 feet above and 8,700 feet below. In cruise, a “normal” selection tracks targets 2,700 feet above and below as well.

L-3 Communications is offering variants of the SkyWatch series it obtained with its January 2003 acquisition of Goodrich Avionics systems. Two variations are available: the SkyWatch HP ($20,990) and the SkyWatch 497 ($15,990).

The HP has a 35-nm display range, a 9,900-foot vertical range, and a 55,000-foot ceiling, and can track 10 targets at once. This device has seen wide use aboard business and regional jets employing Rockwell Collins Pro Line electronic flight information systems. The 497 matches the HP’s performance figures in most areas except display range, which is 11 nm. Both units employ a single, TCAS-type antenna, have internal cooling fans, and come with a five-year warranty.

Passive detection

For owner-operators hesitant to take the TAS plunge, Mode S transponders are probably the next best thing. As with all passive anti-collision systems, these units rely on third-party interrogation and their effectiveness falls off sharply outside of radar coverage areas. These transponders can stand alone on a panel, or their data may be shown on a third-party MFD. Buyers also have the option of taking their transponder in the form of a behind-the-panel module that links directly with an MFD.

Garmin has the GTX 330 panel mount ($4,995) and GTX 33 ($4,195) module systems, while Bendix/King offers the KT 73 ($4,300) in panel mount and module configurations.

Traffic information collected by the Garmin 330/33 systems can be displayed on that company’s 396/496 handheld GPS units, 400/500 series navcom/GPS units, and the G1000 integrated avionics suite. Bendix/King’s KT 73 is compatible with that company’s KMD 250 multifunction display, and others.

Perhaps the biggest advantage of the Mode S transponders is that they are the conduits for TIS, the least expensive of all traffic awareness tools. An FAA-provided service, TIS is connected with 107 ASR-7 and ASR-8 terminal radars located around the U.S. Each of these radars has a software program that recognizes Mode S transponders and uplinks information regarding transponder-identified air traffic within the radar’s effective range.

TIS’s days appear to be numbered, however, as a general phase-out of TIS ground stations has already begun. In April 2005, without consulting AOPA or any other aviation organizations, the FAA issued a decision paper stating the safety benefits of the program did not warrant the cost of providing the service.

The agency identified 22 sites where an upgrade to newer ASR-11 radar will eliminate TIS by 2012. AOPA members decried the move, saying a 25 percent reduction in TIS services eliminates an important safety benefit while compromising the value of their hardware investment. By AOPA’s count, more than 10,000 pilots have equipped their aircraft for TIS.