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MICROWAVE LANDINGSYSTEM

MLS

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ILS REPLACEMENT? MLS is an improvement on the ILS approach

system.

It was developed extensively with the thought thatthe US would run out of ILS channels. (40channels only)

The advent of the GPS along with the high cost ofMLS has insured it will never become amainstream system.

ILS will last until GPS VNAV systems take over asthe primary precision approach system.

There are MLS installations in Europe and the US.

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INSTALLATION  Azimuth transmitter at far end of runway.

Elevation transmitter at near end of runway.

Narrow beams sweep across coverage area at a fixedscan rate.

 Aircraft receiver measures the time interval between

sweeps and calculates azimuth and altitude. Horizontal and lateral navigation information is displayed

on the aircraft CDI, HSI, or MFD. (similar to ILS)

 A precision DME/P installation is incorporated into the

system.  All signals (except DME) are sent on a single frequency

using time sharing. (each type of signal is sent in a specificorder one after the other in quick succession; azimuth,elevation, data.)

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FIVE FUNCTIONS  Approach azimuth: precise horizontal guidance.

Back azimuth: horizontal guidance for missedapproach.

 Approach elevation: precise vertical guidance.

Slant range: DME/P, precision DME accurate to

100ft. (computer compensated slant-range)

Data communication: waypoint coordinates,weather conditions, runway conditions, equipment

status.

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 ADVANTAGES Reliability: freedom from FM radio and terrain interference.(allows for more versatile site selection.)

Flexibility: – Availability of multiple flight paths approaching the same runway.

 – Lateral guidance can vary as much as 60 either side of centerlinewith range to 20nm.

 – Vertical guidance from 0.9 to 15 (helicopters). – Potential for curved and segmented approaches.

 – Data transfer capability.

 – MMLS (mobile MLS) portable deployment for military applications.

 – Capability of providing precision guidance to small landing areaslike rooftop helipads, or aircraft carriers. (ground based equipmenttakes up less space.)

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DISADVANTAGES

Expensive: the initial expense of infrastructure set-

up and aircraft equipment installation. New alternatives: GNSS is emerging as the

mainstream RNAV system for civil aviation. It’s

potential for non-precision and precision approachcapability has been proven. With market forcesdriving GPS usage it is destined to be the system

of the future. MLS will be limited to specialized applications,

such as military MMLS.