Heading

The alignment of the front-to-rear axis of the aircraft, or, in other words, the direction the aircraft is ‘pointing’. It is usually measured and described in Degrees Magnetic. A Heading instruction from a Controller requires the pilot to steer the aircraft along the nominated heading.

History Dots

A visual display on the radar screen of an aircraft’s position at preceding radar sweeps. They appear as a trail behind the current position, and give important visual indications of the speed and direction of the aircraft’s movement.

HMI

See Human Machine Interface

Hotline

A communication system used between controllers that does not require a call to be answered by the receiver. A call initiated by either controller causes the line between them to become active instantly, and communication can commence. It is provided between control positions where urgent and instant contact between controllers may be required.

Human Machine Interface

The interface with which the Radar System (or simulator) provides information to the controller, and with which the controller provides inputs to it.