In
aviation
Aviation includes the activities surrounding mechanical flight and the aircraft industry. ''Aircraft'' includes fixed-wing and rotary-wing types, morphable wings, wing-less lifting bodies, as well as lighter-than-air craft such as hot a ...
, a critical area refers to a designated area of an
airport
An airport is an aerodrome with extended facilities, mostly for commercial air transport. Airports usually consists of a landing area, which comprises an aerially accessible open space including at least one operationally active surfa ...
that all aircraft, vehicles, persons or physical obstructions must remain clear of when one or more
Instrument Landing Systems (ILS) are in use, to protect against signal
interference
Interference is the act of interfering, invading, or poaching. Interference may also refer to:
Communications
* Interference (communication), anything which alters, modifies, or disrupts a message
* Adjacent-channel interference, caused by extr ...
or
attenuation
In physics, attenuation (in some contexts, extinction) is the gradual loss of flux intensity through a medium. For instance, dark glasses attenuate sunlight, lead attenuates X-rays, and water and air attenuate both light and sound at variabl ...
that may lead to
navigation
Navigation is a field of study that focuses on the process of monitoring and controlling the movement of a craft or vehicle from one place to another.Bowditch, 2003:799. The field of navigation includes four general categories: land navigation, ...
errors, or accident. Critical areas also protect the ILS system's internal monitoring{{huh?, date=August 2016.
ILS technology delivers two main types of information to pilots. These types include the glideslope (vertical location relative to the designed glide path) and the localizer (lateral position relative to the designed approach course). Each type of information is broadcast using a separate antenna array and each type has a specific critical area:
* Localizer critical area – aircraft/vehicles/persons or physical obstructions are not authorized in or over the critical area when an arriving aircraft is between the
ILS final approach fix and the airport.
* Glideslope critical area – aircraft/vehicles/persons or physical obstructions are not authorized in or over the critical area when an arriving aircraft is between the ILS final approach fix and the airport unless the aircraft has reported the airport in sight and is circling or sidestepping to land on a runway other than the ILS runway.
For practical purposes, these two areas are combined into the ILS critical area and identified by signs and pavement markings.
During times of reduced ceilings and visibility (800 ft/2 miles) ''or'' during ILS
autoland
In aviation, autoland describes a system that fully automates the landing procedure of an aircraft's flight, with the flight crew supervising the process. Such systems enable airliners to land in weather conditions that would otherwise be dangero ...
(coupled) approaches pilots are expected to:
* Before takeoff – stop aircraft before entering the critical area while waiting for takeoff.
* After landing – move the aircraft out of the critical area before stopping to receive taxi instructions from the ground controller.
Much larger than the critical area is the sensitive area. Aircraft and vehicles are not allowed in this area when low visibility procedures are in force, since aircraft autoland during this time and therefore the accuracy of the guidance signals provided by the ILS is absolutely critical.
Multipathing is a potential error in the ILS system, which may affect the glideslope and/or the localizer. This occurs when the radio signals reaching the aircraft are distorted because a large metal object moves into the radiation zone of the transmitter, such as when an aircraft is flying ahead or a taxiing aircraft or truck enters the ILS critical area.
Air navigation