a flight safety message

an unauthorized message.

an urgency message.

Continuous day and night service.

No specific working hours.

sunrise to sunset.

Sunset to Sunrise.

Karlsgrab Homer, Golf Alfa Charlie Mike Echo request QDM.

Karisgrab Homer, Golf Alfa Charlie Mike Echo request QDR.

Karlsgrab Approach, Golf Alfa Charlie Mike Echo request QGH.

Karlsgrab Approach, Golf Alfa Charlie Mike Echo request QNH.

A system in which radiotelephony communication can be established between aircraft only. 

A system which permits the selective calling of individual aircraft over radiotelephone

channels linking a ground station with the aircraft.

A system provided for direct exchange of information between air traffic services (ATS)

units. 

A system in which radiotelephony communication between two stations can take place in

both directions simultaneously.