MICROWAVE LANDING SYSTEMS

The current Instrument Landing Systems in use at virtually all airports are becoming inadequate for the increasing volume of aircraft.

The replacement system being suggested is the Microwave Landing System which operates on frequencies around 5 GHz which are virtually free from interference. The system also has the advantage of allowing aircraft to lock on to the final approach anywhere within a 25-mile segment-in other words, aircraft can fly a curved approach instead of a straight line approach as with ILS.

However, MLS is expensive for airlines and airports and an alternative system is now under test at Heathrow’s runway 27R. A Boeing 767 of British Airways is testing a satellite navigation aid to bring the aircraft onto the final approach. Any adjustments to the aircraft's position are made by the ground - based station which corrects the Global Position System information so that the aircraft is in the exact position for landing.

The system is known as the Differential Global Positioning System (DGPS).

The advantage for airlines lies in the fact that many of their aircraft are already fitted with GPS equipment so it makes sense to use it for landings.

The 747 will obtain data on DGPS and MLS during the trial so that the two methods can be compared.