What surveillance system requires an aircraft to be equipped with a data link transmitter?

The surveillance system that requires an aircraft to be equipped with a data link transmitter is Automatic Dependent Surveillance-Broadcast (ADS-B). This system relies on an aircraft's own onboard GPS positioning and transmits this information along with other data, such as velocity and intent, via a data link to ground stations and other aircraft.

ADS-B improves situational awareness and provides a means for surveillance without the traditional reliance on ground-based radar systems. It is crucial that aircraft are equipped with the appropriate ADS-B equipment, including a data link transmitter, to participate in this system. This capability enhances the efficiency and safety of air traffic control and is a significant advancement in modern aviation technology.

Other surveillance systems, like primary radar and secondary radar, do not operate on this principle; primary radar relies on the reflection of radio waves off an aircraft, while secondary radar requires transponder signals but does not necessarily use data link transmissions in the same way as ADS-B. Multilateration, while similar in some operational aspects, involves ground stations determining the position of an aircraft using time differences in received signals from the aircraft and typically does not require the aircraft itself to be equipped with a specific data link transmitter.