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Air Law

It has been decided:

- Aircraft flying VFR should set the code to 7000.
- If an aircraft is in an emergency, the code should be set to 7700.

- If an aircraft has a radio failure, the code should be set to 7600.

- If there is an unlawful action (hijacking), the code should be set to 7500.

1.5.3.4 Mode S

Today, a further step has been taken, as the latest transponders now transmit

the aircraft's call sign. This is called mode S (SIERRA).

The system gives the air traffic controller this information directly on their

computer screen, so they immediately know the aircraft's identification, its

altitude, and whether it is ascending or descending.

Additionally, computer systems generate vectors showing the aircraft's

position in the future, based on its current direction and speed. The air traffic

controller can then see if there is, or will be, conflicting traffic.

Here is the signal from a single aircraft on a

radar-generated computer screen.

Here is a radar image from a visit to

EKKA.

The green patches represent areas

of precipitation.

OY-BKA is located west of Tange

Lake on its way to perform a GCA

approach. The aircraft does not

have a mode S transponder, but the air traffic controller manually enters the

call sign into the computer.

There are currently 9 radars in Denmark, connected electronically so that an air

Flight Theory PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 71