Lecture 8- M icrowave L anding S ystem (MLS)

1. Lecture 8- Microwave Landing System (MLS)

2. Definition Microwave • an electromagnetic wave with a short wavelength in the range 0.001–0.3 m.

3. INTRODUCTION • U.S. airlines began using ILS approaches on a regular basis after World War II, and by 1949, the ILS had become the world standard for landing guidance systems. • By the late 1960s, however, air traffic congestion and the need for more noise sensitive approach paths to airports had begun to demand a more capable and flexible landing system.

4. INTRODUCTION • One problem with ILS was that the VHF/UHF frequencies in which it operated had a limited number of channels. • As air transportation became more popular, planners began to see a time when certain areas of the country would have more airports requesting instrument landing systems than the ILS frequency range could accommodate. • The relatively low frequency range of the ILS was also susceptible to signal reflection, or "multipath," errors.

5. Introduction • MLS (Microwave Landing System) was developed to improve the uses of ILS system, however only few Airports have MLS installations. • MLS is an advanced precision approach and landing system. • MLS provides position information in a wide coverage sector and is determined by: • Azimuth angle measurement (horizontal) • Elevation measurement(vertical) • Range measurement

6. MLS Ground Installations An MLS azimuth (horizontal) guidance station

7. MLS Ground Installations An MLS elevation (vertical) guidance station

8. MLS Coverage

9. How MLS works? • MLS operates in the Super High Frequency (SHF) between 5031 – 5090 MHZ (5.031-5.090GHz). • MLS use passive electronically scanned arrays to send scanning beams towards approaching aircraft. • An aircraft that enters the scanned volume uses a special receiver that calculates its position by measuring the arrival times of the beams. • MLS provide large coverage signals even in very poor visibility. • As MLS signals have large coverage, this will increase runway utilization. • MLS also has more channels which can avoid the signal interferences.

10. Examples • Aircraft flying into Heathrow Airport in fog or poor visibility will be guided in using a new Microwave Landing System. • On a clear day, about 44 planes an hour land at Heathrow. However, if the visibility drops and aircraft have to use the ILS system to land on full autopilot, that figure falls to 24 aircraft an hour. • This is because the radio transmitter at the end of the runway needs good line of sight to the approaching aircraft, but because it is at the far end of the runway, planes have to land and taxi clear before a full signal is restored. • The new MLS allows an extra six aircraft an hour to land, meaning that while fog will still cause disruption, its effects will be less prominent.