Plain English Meaning

The ways an ILS approach signal can be wrong or misleading. Even though the cockpit needles look normal, the signal itself may be distorted or the pilot may be tracking a false beam that looks correct but isn't.

Full Definition

The collective term for inaccuracies and false signals that can affect an Instrument Landing System (ILS), causing the localizer or glideslope indications in the cockpit to be misleading or unreliable. These errors arise from signal reflections off buildings, terrain, or aircraft on the ground, from interference, from receiver limitations, and from or false glideslopes that occur at angles other than the .