Page 903 - PPL-engelsk 2025

Navigation

We set the selector switch to SBY (Stand By) when we reach the point in the

checklist during the start-up of the electrical equipment. In this position, the

transponder warms up so that it is ready when we set the transponder to ON on

the runway just before take-off.

In the ON position, the transponder sends the 4 digits that have been turned into

the 4 windows. The transponder sends a secondary response signal in mode A

(ALPHA).

If the selector is set to ALT, information about the aircraft's altitude is sent with

the response signal. However, this only happens if the aircraft is equipped with

an encoder that provides the transponder with information about the aircraft's

pressure altitude (altitude relative to 1013 HPa). When the transponder sends

information about altitude, we say that it is in mode C (CHARLI).

If the aircraft is equipped with a transponder, it must be turned on during flight.
If the transponder has mode C, it must be in the ALT position.

9.10.4.4 Squawk codes

It has been agreed that aircraft that:

- are flying VFR, set the code 7000

- are in an emergency, set 7700

- have radio failure, set 7600

- are subject to an illegal act (hijacking), set 7500.

9.10.4.5 Transponder modes

The transponder has different modes.

Mode A (ALPHA): In the ON position, the transponder sends the 4-digit

identification transponder code (Squawk code) that has been entered.

Flyveteori PPL(A)(UL)/LAPL Henning Andersen, Midtjysk Flyveskole© 2025 903