Instrument Landing System
Overview
Instrument approach
For aircraft operating under instrument flight rules , an instrument approach or instrument approach procedure is a series of predetermined maneuvers for the orderly transfer of an aircraft under instrument flight conditions from the beginning of the initial approach to a landing, or to a point...
system that provides precision guidance to an aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...
approaching and landing on a runway
Runway
According to ICAO a runway is a "defined rectangular area on a land aerodrome prepared for the landing and take-off of aircraft." Runways may be a man-made surface or a natural surface .- Orientation and dimensions :Runways are named by a number between 01 and 36, which is generally one tenth...
, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument meteorological conditions (IMC)
Instrument meteorological conditions
Instrument meteorological conditions is an aviation flight category that describes weather conditions that require pilots to fly primarily by reference to instruments, and therefore under Instrument Flight Rules , rather than by outside visual references under Visual Flight Rules . Typically, this...
, such as low ceilings or reduced visibility due to fog, rain, or blowing snow.
Instrument approach procedure charts (or approach plate
Approach plate
Approach Plates is a common term used to describe the printed procedures or charts, more formally Instrument Approach Procedures, that pilots use to fly approaches during Instrument Flight Rules operations. Each country maintains their own instrument approach procedures according to International...
s) are published for each ILS approach, providing pilots with the needed information to fly an ILS approach during instrument flight rules (IFR)
Instrument flight rules
Instrument flight rules are one of two sets of regulations governing all aspects of civil aviation aircraft operations; the other are visual flight rules ....
operations, including the radio frequencies used by the ILS components or navaids and the minimum visibility requirements prescribed for the specific approach.
Radio-navigation aids must keep a certain degree of accuracy (set by international standards of CAST/ICAO); to assure this is the case, flight inspection
Flight inspection
The evaluation process, using properly equipped aircraft, regarding continuity, integrity and accuracy of significant parameters from radio navigation aids and procedures, aiming their calibration with international standards....
organizations periodically check critical parameters with properly equipped aircraft to calibrate and certify ILS precision.
An ILS consists of two independent sub-systems, one providing lateral guidance (localizer
Localizer
In aviation, a localizer is one of the components of an Instrument Landing System , and it provides runway centerline guidance to aircraft. In some cases, a course projected by localizer is at an angle to the runway . It is then called a Localizer Type Directional Aid...
), the other vertical guidance (glide slope or glide path) to aircraft approaching a runway.
