Terminology » Other Wireless » Microwave Landing System (MLS) Basics

Microwave Landing System (MLS) Basics

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MLS stands for Microwave Landing System. It’s an approach landing navigational aid that guides aircraft using curved, straight, or segmented flight paths for landing. The primary outputs of MLS include bearing, slant distance, and altitude in the approach terminal area. Notably, MLS is primarily used by the military due to its flexibility in approach landings, unlike the Instrument Landing System (ILS) commonly used in civilian aviation.

MLS Microwave Landing System

Ground-Based Features

Here’s a breakdown of the features of both the Azimuth Transmitter (Tx) and Elevation Tx on the ground:

Azimuth Transmitter (Tx)

  • Function: Provides bearing information.
  • NAV: Horizontal Guidance.
  • Quantity per runway: 2
  • Location: One is placed at the end of the runway, and the other at the beginning.
  • Frequency of operation: SHF (5.031 to 5.0907 GHz) with 200 channels.
  • Horizontal Range of Operation: 37 km
  • Deviation from Centerline: Approximately +/- 40 Degrees.

Elevation Transmitter (Tx)

  • Function: Provides altitude (ALT) information.
  • NAV: Vertical Guidance.
  • Quantity per runway: 1
  • Location: On the side of the runway.
  • Frequency of operation: SHF (5.031 to 5.0907 GHz)
  • Number of Channels: 200
  • Vertical Range of Operation: Approximately 6 km
  • Typical MLS Inclination: About 8 Degrees
  • Deviation from MLS: Approximately +/- 7 degrees

Aircraft System

In the aircraft, the MLS receiver system operates in the SHF band. The primary outputs from MLS are bearing/slant distance and altitude. Secondary outputs include meteorological information, runway status, etc.

Advantages of MLS

  • Improved guidance accuracy with greater coverage area.
  • Provides flexible landing path navigation.
  • Offers guidance for missed approaches and departure navigation.
  • MLS has low sensitivity to weather conditions and airport ground traffic compared to ILS.
  • MLS offers 200 frequency channels, 10 times more than ILS.
  • Maintenance and installation of MLS are cheaper.

Disadvantages of MLS

The use of Microwave Landing System is not widespread in civilian aircraft.