Localizer (LLZ, LOC) Parameters

The Localizer generates an RF−signal in the frequency range of 108 to 112 MHz, which is modulated in amplitude with 90 and 150 Hz. This signal identifies the "course plane" and is produced by a transmitter and antenna system, which can be a 2F system with 25 W transmitter power or a 1F system with 30 W transmitter power. The localizer signal is obtainable up to a distance of up to 25 nautical miles (approx. 46 km) for a sector of ±10°, and it is obtainable up to a distance greater than or equal to 17 nautical miles (approx. 31 km) for a sector of ±35° relative to the course line and the Localizer−antenna. The characteristic values for LLZ within certain sectors, and in relation to the runway centre line, are as follows:

• Difference in Depth of Modulation (DDM) = 0
• DDM = 15.5 % (0.155)
• DDM greater than or equal to 18 % (0.18)

DDM 0 occurs when the approach direction corresponds exactly to the runway centre line. DDM 15.5 % occurs at the course sector selected such that the boundary at the level of the runway threshold is about 105 m to the left and right of the runway with respect to the centre line, which points are known as WIDTH points. The DDM has a linear characteristic within these points and an elevation of 0.00145 DDM per meter. This results in approx. 105 m for the half sector calculated for DDM=15.5 %. ICAO Annex10 (4th Ed., April 85, section 3.1.3.7.3).

DDM greater than or equal to18 % shows a sector of ±10°and DDM greater than or equal to15.5 % characterizes a sector of ±10° to ±35° where correct LLZ information is still obtained. In the LLZ−1F, this sector is covered by a specifically formed antenna pattern, and, in the LLZ−2F system, it is covered by an additional Clearance signal. The Course information consists of 90 and 150 Hz amplitude−modulated signals. When the aircraft is approaching the runway on the desired course, the air−borne receiver receives the two modulation signals with equal amplitudes. This state corresponds to DDM 0.

If there is a leftward deviation from the desired course, there will be a predominant 90 Hz amplitude, and if there is a rightward deviation there will be a predominant 150 Hz amplitude.