July 20, 2018, ©. Leeham News: Last week we discussed how a TCAS (Traffic Collision Avoidance System) works and how ADS-B will improve the system.
Now we discuss other areas of aircraft navigation and separation which are enabled when all players have ADS-B and transmit their 3D position and where they are going.
When all aircraft in controlled airspace have ADS-B it changes the way Air Traffic Control (ATC) separates and directs aircraft.
Air traffic is increasing by 6%-7% year over year. Figure 1 shows the intensity of airliners flying in different parts of the world.
With separation and control tools like Radar and Secondary Radar (by means of transponder responses), there is a limit how many aircraft can share an airspace.
With the increased position accuracy of ADS-B, the separation between aircraft can be reduced. This allows a higher traffic volume for the same airspace.
The first area where ADS-B has been used to reduce separation requirements is in areas with no radar coverage, such as Oceanic airspace. Normally aircraft must operate with large separations as so-called “procedural separation” is used. It builds on pilots reporting the aircraft’s position over HF radio (the normal VHF radio hasn’t the range) or datalink (FANS-1/A via satellite) at regular intervals. Air Traffic Control then establishes separation by queuing aircraft in long trains at near optimal altitudes and at the same airspeed.
The drawback is the aircraft must fly after one another on common tracks, at the same speed and stay on the same flight level as long as any conflict risk with other aircraft exists. With low positioning knowledge by ATC, the clearance to climb to a better flight level to fly more efficiently (as the aircraft gets lighter) or overtake a slower aircraft is often difficult to get, It often takes time until a secure separation is achieved and the climb can be allowed. The ATC is simply not sure where all aircraft are and cannot allow any fast movements in the air-space. The result is long trains of aircraft with many flying in a non-optimal way.
With ADS-B in every aircraft, one can install an aircraft to aircraft separation application which allows the pilot requesting the climb to include the nearest aircraft and the observed separation to these in the climb request. The controller knows the aircraft has the equipment to self-separate and allows the pilot to change altitude.
ADS-B also enables a simplified and cheaper TCAS system to be installed on general aviation aircraft. Only a software application is needed in the avionics system which takes the ADS-B reports from surrounding aircraft and calculates collision risks.
It then gives Traffic Awareness messages to the pilot through audio (“aircraft 2 o’çlock same altitude five miles”) and on the flight displays.
In the next Corner, we will discuss how radio traffic will gradually be replaced with Chat between the pilot and the air traffic controller.