By By Bjorn Fehrm for Leeham News
Last week we started a series of Corners that deal with the largest navigation change since VOR and Radar was introduced after the Second World War.
It's about leaving radars and transponders to keep track of where aircraft are, letting an ADS-B transmitter/receiver in the aircraft take over this role.
ADS-B, the future navigation cornerstone
Most people think of the ADS-B system (Automatic Dependent Surveillance-Broadcast) as an extension of the aircraft's transponder.
Principally, it's not. It's operating principle is totally different. A transponder answers to someone interrogating it. The ADS-B doesn't. It just shouts out its message every second, whether someone is interested or not.
Where it has links with advanced transponders (the type S) are, all ADS-B solutions outside of the US and most in the US use the mode S transponder's 1090Mhz datalink transmitter for sending the message. The message format is an extended version of the type S transponders datalink message called Extended Squitter (ES) message.
In the US, an alternative ADS-B datalink is allowed to lessen fears of congestion for the 1090Mhz ES link. It's a data link transceiver at 978Mhz, called the UAT (Universal Access Transceiver), which is allowed below 18,000ft altitude. The idea is general aviation aircraft which don't fly above 18,000ft could use the 978Mhz link and by it reduce congestion for the 1090Mhz link.
The message these datalinks transmit is the one we described in the last Corner:
- Who the aircraft is;
- Where the aircraft is;
- Where it's heading, at what altitude and at what speedl
- If it's climbing or descending; and
- If it's in distress.
Where is ADS-B mandatory?
In the US, ADS-B must be...