ADS-B'A New Technology For Traffic Identification

by Charlie Spence, Aviation Writer and IFA Member

When you're cruising along in marginal VFR weather wouldn't it be comforting to know what aircraft are in your vicinity even before ATC alerts you?  A new technology now getting underway will do just that.  It's called Automatic Dependent Surveillance-Broadcast (ADS-B). The FAA is just getting it started but you can expect it to be expanded to where almost every aircraft will have this equipment aboard.

ADS-B uses global positioning system technology to broadcast a radio transmission approximately once per second containing the aircraft's position, velocity, identification, and other information. It can also receive reports from other suitably equipped aircraft within reception range. This information appears on a screen in the cockpit. Thus, besides ground control knowing what aircraft are where, the interchange between equipped aircraft provides that information directly to each airplane faster than it can be seen by ground units and relayed to the aircraft. (Surveillance radar sweeps every six seconds.)

These ground-based transceivers provide surveillance services, but the ground infrastructure is not necessary for ADS-B equipped aircraft to detect each other.

This new technology will be particularly useful in areas where terrain makes radar useless or where cost of installation of radar is impractical. Two different data links have been adopted for use with the ADS-B: 1090 MHz Extended Squitter and the Universal Access Transceiver. The 1090 link is for aircraft above flight level 18, while the Universal is for those that primarily use altitudes below flight level 18. Pilots will see no difference in the two.

The avionics allow the pilot to enter the aircraft's call sign and Air Traffic Control's transponder code. This information is transmitted to other equipped aircraft and to the ground stations. Because some ADS-B panels are not connected to the transponder, it is essential that the transponder code is identical in the two instruments. The system provides a VFR privacy mode switch that may be used by pilots not wanting to receive air traffic services. This broadcasts to other aircraft VFR identification similar to the 1200 transponder code.

ADS-B operates on the ground as well as in the air so is expected to be an aid in reducing runway incursions.

The initial installation of ground stations is along the East Coast from New Jersey to Florida. It will be perhaps another ten years before the ground portions are nation wide. Currently, the air-to-air applications are for advisory use only. There is expectation, however, that the equipment will be mandatory in certain airspace in coming years.

Traffic Information Service Broadcast (TIS-B) is the broadcast of traffic information from ground stations to ADS-B equipped aircraft. TIS-B service is becoming available in a selected few locations where there are both adequate surveillance coverage from ground sensors and adequate broadcast coverage from Ground Based Transceivers. Of course, only properly equipped aircraft can receive the TIS-B. Only transponder-equipped aircraft are detected and this service is not intended to relieve a pilot of responsibility to 'see and avoid' other traffic.

This development can be a step in permitting more growth in aviation. The present Air Traffic Control System has its limits. Just as the telephone system had to move to the dial system and eliminate the one-on-one telephone operator method to accommodate growth, air traffic must move on from the one-on-one controller to aircraft system and arrive at what some general aviation persons were calling for nearly a half-century ago. That is, control by exception in which ground controllers contact aircraft only if they deviate into dangerous situations.