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 false courses or false glideslopes that occur at angles other than the intended approach path.
Plain English
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.
Context Anchor
Seen during instrument approach training and approach briefings, especially when learning the limits and possible faults of ILS guidance.
Derivation
Error comes from a Latin word meaning “to wander” or “go astray.” That helps here because an ILS error means the guidance indication has wandered away from the true path the pilot is trying to follow.
Why Pilots Care
Unrecognized ILS errors can produce an unstable approach or force a missed approach, increasing workload and risk near the ground.
Intuition Check
Do not assume “ILS errors” means the pilot made a mistake. Here, it means the ILS guidance itself may be inaccurate, disturbed, or unreliable.
Example Sentence 1
The instructor explained that ILS errors can be caused by a large aircraft taxiing through the localizer signal, which is why ground controllers protect the critical area during low-visibility approaches.
Example Sentence 2
The crew flew the approach at a slightly higher speed to allow extra time to detect any ILS errors on the glide slope.