How a digital control tower works

1. On the airfield: the sensors

A conventional tower gives controllers a view from a glass cab. A digital tower puts the view on a mast instead, and adds what the eye cannot do.

Panoramic cameras

Fixed high-resolution cameras together cover the full circle of the airfield: runways, taxiways, aprons and the traffic pattern. Their images are stitched into one panorama on the controller's screens. General Aviation's mast, for example, carries 14–18 fixed 4K panoramic cameras.

Pan-tilt-zoom cameras

Pan-tilt-zoom (PTZ) cameras do the job of binoculars in a tower cab: close-ups of an aircraft on final, a vehicle near the runway, or landing gear before touchdown. Systems can point them automatically at a selected aircraft and keep it in frame.

ADS-B and surveillance data

An ADS-B ground station receives the positions that equipped aircraft broadcast. The system matches those positions to what the cameras see, so aircraft appear boxed and labelled with their call sign. Some projects also bring in radar tracks: the Northern Colorado Regional Airport demonstration combined video with track-based surveillance.

Radio and airfield audio

Radios on the airfield transmit and receive on the tower and ground frequencies, and can monitor the emergency frequency. A microphone carries the sound of the field to the controller, which helps when an aircraft is heard before it is seen, or in poor visibility.

Weather, lights and the rest

Weather inputs feed the station so the controller can give current wind and altimeter settings. A light gun signal lets the controller signal aircraft without a working radio, as a tower would.

2. The link

Video and sensor data travel from the mast to the controller station over a data link. Latency matters: the controller must see what is happening now. General Aviation, for instance, designs to under one second of latency on a closed point-to-point fiber link with no wireless. The link's security and what happens when it fails are among the most important questions to ask any supplier.

3. The controller station

The station is where the controller works: a wall of screens showing the panorama, PTZ views and labels, with radio and the light gun at hand. Software helps without deciding. Typical aids include:

Tracking: aircraft and vehicles boxed and labelled on the video.
Runway monitoring: an alert if something enters a runway that should be clear.
Conflict alerts: a warning when two aircraft get too close.
Prepared instructions: current weather formatted for broadcast, standard taxi routes drawn for the controller to approve.

The station can sit at the airport or far from it. That is what makes remote operation possible: one controller can serve a field where no one could be recruited, and a centre can house positions for several airports.

4. In the cockpit

For pilots, a digital tower sounds like any tower: the same frequencies, the same phraseology, the same clearances. General Aviation's system needs no new equipment in the aircraft beyond standard VHF radios and transponders, and offers an optional companion app that shows a transcript of each transmission, the taxi route on an airport diagram, and the pattern entry.

What a digital tower replaces

The tower building and its cab, with the land, construction and upkeep they need.
The need for controllers to be physically on the airfield.
Dependence on what can be seen from one window, by adding night, low-visibility and surveillance inputs.

What it does not replace

Controllers. A certified controller issues every clearance. The software flags; the person decides.
FAA approval. The regulator approves the system and decides on the service and the airspace around the airport.
Pilots' responsibilities. See-and-avoid, radio calls and the rules of the airspace still apply.
Approach and en-route control. A digital tower provides tower services at and around one airport, not radar approach control.