Airspace Class A: Only IFR flights are permitted; all flights receive ATC service, are separated from each other, and require ATC clearance; continuous radio communication is required.

A CTR (Control Zone) is controlled airspace extending from the ground to a specified upper limit, which usually protects one or more airports and approach and departure procedures.

An RMZ (Radio Mandatory Zone) is an airspace of defined size in which suitable radio equipment must be carried and continuous listening readiness or, if necessary, two-way radio communication on the specified frequency must be ensured (according to national regulations).

A TMZ (Transponder Mandatory Zone) is an airspace of defined extent in which the carriage and operation of SSR transponders (Mode A/C or Mode S) is mandatory, unless alternative requirements apply.

DME (Distance Measuring Equipment) is a radio navigation aid for measuring the distance (slant range) between an aircraft and a ground station by measuring the transit time of pulses; it provides distance but not direction.

An NDB (Non-Directional Beacon) is a radio transmitter in the LF/MF range that emits a signal of equal strength in all directions; with ADF receivers on board, the direction (bearing) to the NDB can be determined.

VOR (VHF Omnidirectional Radio Range) is a VHF radio navigation system that provides bearing information: the aircraft can use the VOR signal to determine the magnetic bearing (radial) to/from the ground station.

FLARM is a short-range collision warning and traffic awareness system (primarily for gliders/general aviation) that determines its own position and altitude (GNSS + barometric), transmits this information via radio, and detects and warns of conflicts with other FLARM participants based on a movement forecast.

The transponder code (SSR code/squawk) is a four-digit octal code that is set in the transponder and is used for identification/handling by ATC. Standard emergency codes are 7700 (emergency), 7600 (comms failure), and 7500 (unlawful interference).

A transponder is an onboard radio device that automatically responds to SSR queries from ground radar or other systems and, depending on the mode, transmits identity code, altitude, and other data to identify and monitor aircraft.