MLS

Question 1

What is MLS?

Answer 1

Microwave landing system and was designed to replace ILS, however this never quite came to fruition because GPS based Wide Area Augmentation System (WAAS) also advanced in parallel with MLS.

Question 2

What are the advantages of MLS over ILS?

Answer 2

• over 200 channels compared to ILS 40.
• Not limited to straight in and long approaches.
• Signals are swept in fan shape movement compared to long narrow
beam of ILS, thus making MLS more accurate
• Back course transmissions provides missed approach and dept
guidance to 10nm, 10,000ft, + 20˚azimuth and 15˚ elevation
• can operate from unprepared hilly sites
• no multi path interference
• built in DME
• Compatible with ILS, WAAS and existing auto pilot systems

Question 3

What is the principle of operation of MLS?

Answer 3

Its uses one freq to transmit all data using MLS TDM (time division multiplexing).

1 freq delivering info in packets compared to ILS which switches between VHF and UHF.

Question 4

What are the MLS freq band?

Answer 4

5031 to 5091mHz
SHF

At 300khz spacing

Question 5

How is an MLS ident?

Answer 5

4 letters and no.s starting with the letter ‘M’.

The ident is transmitted 6times/min

Question 6

What is the area of coverage of an MLS?

Answer 6

40˚ either side of the centreline horizontally

20nm vertically, so 0.9˚ or 20˚ vertically

Question 7

What is the accuracy of MLS?

Answer 7

• 95% lateral
• 20nm Vertical
• 60’ above the MLS datum point

• When used with a CAT III system, accuracy is + 20’ in azimuth,
+ 2˚ in elevation

Question 8

MLS A/C displays must be fitted with what to work?

Answer 8

A multi mode receiver (MMS)

Question 9

Segmented and curved MLS approaches can be executed at airfields only with what installed?

Answer 9

DME/P

With out DME/P an ILS look alike straight one approach can still be flown using MLS equipment.