ILS Critical Area

Sign placed at edge of ILS critical area (often next to pavement markings)

ILS critical area boundary sign

ILS Critical Area

The ILS (Instrument Landing System) critical area is a designated area near the localizer and glide path antennas where vehicles and aircraft are excluded during ILS operations to prevent interference with the guidance signals.

Purpose

The critical area is protected because the presence of vehicles or aircraft within its boundaries can cause unacceptable interference to the ILS signal, potentially disrupting the precision guidance provided to landing aircraft.

Location

The critical area is located around the localizer (azimuth guidance) and glide path (elevation guidance) antennas.

Protection

To protect the critical area, vehicles and aircraft are typically prohibited from entering or moving within its boundaries during ILS operations.

Air Traffic Control (ATC) Role

ATC plays a crucial role in protecting the ILS critical area by issuing instructions to pilots to hold short of the critical area when an aircraft is on an ILS approach, especially when weather conditions are below a certain threshold (e.g., ceiling less than 800 feet or visibility less than 2 miles).

Significance

Proper protection of the ILS critical area is essential for ensuring safe and reliable ILS operations, particularly during low-visibility conditions when pilots rely heavily on the ILS guidance for landing.

Related Terminology

• ILS Sensitive Area – An area extending beyond the critical area where vehicle movement and parking are also controlled to further minimize the potential for interference.
• Holding Position Markings – Yellow markings on taxiways that indicate where aircraft must stop before entering the ILS critical area.

Factors Affecting ILS Critical Area

The size and shape of the ILS critical area can vary depending on factors such as the type of ILS equipment, the aircraft sizes, and the airport geometry.

Reference

Sporty's Flight Training Central