June 2008 Issue

Riding The Beam

When the weatherís down, stay on the ILS glideslope. Itíll take you where you want to go.

The instrument landing system (ILS) is a really wonderful gadget. When everythingís working as it should be, gently keep the aircraft aligned with the transmitted electronic beam, wait long enough and a runway materializes where only a few moments before there was nothing. Pure magic. Its basic technology was perfected long ago, and the fact it remains the primary precision approach is truly remarkable. Of course, the ILS is not without its limitations. For one, it requires substantial site preparation and cannot be installed at just any airport or runway. Its basic characteristics require understanding, too, including the likelihood of false glideslopes, back courses and the possibility of interference from nearby buildings and aircraft. To function correctly, the localizer and glideslope antennas must be placed in specific locations; not all runway environments can accommodate these requirements.

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