In-flight verification of instrument landing system signals

Abstract

An instrument landing system (ILS) provides signals in space receivable by an aircraft in flight to identify, for example, a point in space at which to start an approach along a glide slope path to a touchdown point on a runway. Atmospheric, ground and other conditions may cause transmission anomalies, so that the ILS signals identify a point in space displaced from its intended position. Systems and methods employed in flight use GPS or other positional data to determine the current displacement of such point, as identified by received ILS signals, from its intended position consistent with ILS specifications. In addition to reception and use of ILS and GPS signals, data on geographic runway location and correct ILS signal in space parameters is used for reference purposes in determining signal in space position discrepancies, glide slope path angular discrepancies, or both. The pilot can be alerted not to rely upon the ILS when discrepancies, which can vary on a short time basis and not be discernable from the ground, are determined to exceed safe limits.