5. PREVENT AIRCRAFT FROM ENTERING INSTRUMENT LANDING SYSTEM (ILS)
Restrict aircraft and vehicles from operating within the ILS critical area when required by weather
conditions to do so. This restriction is necessary to preserve the integrity of ILS course signals and to
meet obstacle clearance needs. Airport operators are responsible for installing and keeping proper signs
and markings identifying taxi lanes, hold lines, and no-parking areas associated with ILS critical areas.
For holding purposes, no point on the longitudinal axis of the aircraft is permitted past the hold line. If
an ILS critical area is marked and identifiable, restrict aircraft and surface vehicle operations and
provide the information below when the ILS is being used for approach or landing guidance.
a. Obstacle Critical Area
A rectangular obstacle critical area (Figure 1-4) surrounds the approach end of each Category II
and Category III ILS runway. When conditions are reported such as ceiling less than 200 feet, runway
visual range (RVR) 2,000 feet or less, or both, do NOT authorize vehicles or aircraft to be in the area
when an aircraft conducting an approach or missed approach enters or is over the area.
Figure 1-4. Obstacle critical area