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Interview with Jonathan Bernays - 11/20/00

Summary: Mode S, a way to use radar as a secondary surveillance, and a package data link. The primary motivation for a new system was the interference generated by ATCRBS. TCAS was what made Mode S real, and what entrenched Mode S as a lasting technology. TIS is for people with no TCAS; it provides a subset of TCAS functionality

  • Mode S: a way to use radar as a secondary surveillance, and a package data link. The primary motivation for a new system was the rf interference generated by the ATCRBS. The pulse repetition frequency of the sliding windows environment (what they called the beam sweep when it sweeps through a transponder antenna) was such that it required 15-20 replies per transponder per scan By switching to monopulse, this can be reduced to 5-6 replies/scan. Besides, once the decision was made to use a mode select system, monopulse was pretty much required. Also, keep in mind that monopulse was not something special about Mode S. At the time, monopulse was already being used in Europe!

  • TCAS was what made Mode S real, and what entrenched Mode S as a lasting technology. Because of some midair collisions in the 1970'sq, the U.S. mandated protection of civil airliners. We already have info on this, about requiring TCAS I and TCAS II on large airlines. The interesting thing is that the mandate applies for ALL planes that serve the U.S., so international airlines weren't too happy about that (but they had to deal).

  • There was a huge collision-avoidance debate in the early 1980's. Should it be mediated by ground controllers, and be subject to the limits of human vision/perception and limited communication between airborne traffic? Or should it rest on the "ubiquity of air-to-air communication"?

  • TIS is for people with no TCAS; it provides a subset of TCAS functionality, and aids in "see and avoid" maneuvers. TIS also uses a Mode S transponder, but is much cheaper than a TCAS system, which costs on the order of hundreds of thousands of dollars.

  • "Aviation is expensive, and certification is difficult. No one wants to be the first to explore new technology because of that."



  • The Story of Mode S: An Air Traffic Control Data Link Technology last modified: 12.06.2000