Page 408 - PPL BEG-engelsk

Communication

It has been agreed that:

- aircraft flying VFR set the code 7000.

- aircraft is in an emergency; the code 7700 is set.

- aircraft has a radio failure; the code 7600 is set.

- aircraft is subject to unlawful interference (hijacking), the code 7500 is set.

Today, new transponders send the aircraft's call sign, for example, OY-CTZ. This

is known as mode S (SIERRA).

The newest system provides flight controllers with this information directly on

their computer screens, so they are immediately aware of the aircraft's

identity, flight altitude, and whether it is climbing or descending.

Additionally, computer systems generate vectors showing the aircraft's future

position based on current flight direction and speed. The flight controller can

then see if conflicting traffic is or will be present.

Here is a signal from a single aircraft on a radar-

generated computer screen.

Assigning an individual SSR code for a VFR flight does not imply that the flight

is continuously monitored on radar, or that the flight has received clearance to

enter controlled airspace areas, which, according to air traffic rules, BL 7-1, pkt.

4.6.1.1, must be conducted as controlled flights.

There are currently 9 radar stations in Denmark electronically connected, so,

for example, a controller in Karup can see aircraft taxiing on the ground at

Kastrup.

The transponder is not a guarantee against collision, but it can reduce the risk

of collision.

With mode C, you can also enter class C airspace.

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© marts 2026 408