Microwave Landing Systems (MLS)

Introduction

Microwave Landing Systems are advanced technology designed to replace Instrument Landing Systems (ILS).
Rarely used in practice and not implemented in major or regional airports.
Still part of the ATPL (Airline Transport Pilot License) syllabus despite limited practical relevance.

Emergence of GPS:
- GPS-based navigation is highly accurate and reliable.
- Does not require ground-based equipment, unlike MLS.
High cost of upgrading existing ILS to MLS.
MLS was introduced when GPS technology was becoming dominant.

Uses microwaves in the super high frequency range (3-30 GHz).
Specifically operates between 5.031 and 5.090 GHz.
Utilizes two beams for navigation:
- Elev: Vertical beam
- Aim: Horizontal beam
Signals are distinguished through multiplexing, allowing multiple signals at different identifiers.
Incorporates a Precision Distance Measuring Equipment (DME) for more accurate distance calculations.

Allows for complex approach procedures:
- Curved routes and waypoints in three-dimensional space.
- Potential for routing around obstacles like mountains and valleys.
Horizontal guidance through a fan-shaped vertical beam:
- Coverage: 40° either side of the centerline, up to 20 nautical miles.
Vertical guidance similarly provided by a horizontal fan-shaped beam:
- Coverage: 0.9° to 20° elevation, up to 20 nautical miles.
Precise timing of sweeps provides accurate position information.

Subject to similar interference as ILS (e.g., reflections off vehicles or obstacles).
Requires safe zones around transmitters to protect signal integrity.
MLS beams can be interrupted to avoid reflections from known obstacles, but not a foolproof solution.

MLS overshadowed by GPS due to latter's cost-effectiveness and reliability.
Limited practical use and no firsthand industry experience shared by the lecturer.
Future studies will focus more on GPS systems due to their prominence in navigation.