Civil aviation secures protection of MLS spectrum

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Representatives of the civil aviation community have secured the preservation of spectrum for microwave landing systems (MLS), one of the priority issues put forward by the industry at this year’s World Radiocommunications Conference (WRC) in Geneva.

It follows a gradual revival of MLS as an option to provide precision approach capability at main airports owing to the lack of availability of suitable satellite-based landing systems – which had originally been expected to supersede MLS. Several airports have pressed ahead with installation of MLS to maintain operations in low visibility.

Aeronautical radionavigation services have been allocated frequencies in the 5-5.250GHz range with the 5.030-5.150GHz sub-band for MLS currently the only defined aeronautical function within this range.

MLS channels presently occupy only part of this sub-band – from 5.030GHz to 5.091GHz – but ICAO expects to need channels above 5.091GHz for future MLS expansion.

“Although satellite navigation systems could provide a future solution, MLS can be implemented now and is already operating at certain highly-congested airports,” says a spokeswoman for the Air Transport Action Group (ATAG). “It is anticipated that the number of air and ground MLS installations will increase and that they will need to operate in this extension band.”

The WRC’s Committee 5 panel has granted a request to preserve the current allocation of spectrum for MLS by overhauling an old resolution passed in 1995.

This updated resolution also requires studies on compatibility between new aeronautical radionavigation services and commercial fixed-satellite services in the 5.091-5.150GHz frequency band – although there are indications that, given enough geographical separation, MLS receivers and fixed-satellite stations can co-exist.

“In a nutshell the current regulatory mechanism for MLS will be maintained,” says the International Telecommunication Union (ITU), which hosts the conference.

Although the fixed-satellite service was due to become secondary in status to aeronautical services from 2010 the updated resolution extends this deadline to 2018.