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Navigational aids (NAVAIDS) are used in Aviation for aiding safe airports operation. It is a broad category encompassing radio beacons, light emitting sources, radar, GPS, in fact any device that provides information related safe aviation. NAVAIDS are extremely important to guiding an aircraft to a safe landing regardless of any types of weather, and airport safety is directly affected by their continuous and accurate performance.



NDB is primarily a short distance navigational aid.
NDB is basically a simple transmitter radiating an omnidirectional signal which is modulated at intervals with the identification code. NDB may be sited in association with ILS, or in some cases two NDBs are sited to provide an instrument approach to landing.


With VOR, a pilot can simply, accurately, and without ambiguity navigates from Point A to Point B. VOR facility transmits two signals at the same time. One signal is constant in all directions, while the other is rotated about the station. The airborne equipment receives both signals, looks (electronically) at the difference between the two signals, and interprets the result as a radial from the station.


The DME is to present the pilot with bearing and distance information for the aircraft’s position to be identified. DME operates in the UHF frequency band however its frequency can be "paired" with VOR or ILS (or LLZ and G/S) frequencies.


The ILS is a ground-based instrument approach system that provides precision guidance to an aircraft approaching and landing on a runway, using a combination of radio signals and, in many cases, high-intensity lighting arrays to enable a safe landing during instrument meteorological conditions (IMC), such as low ceilings or reduced visibility due to fog, rain, or blowing snow. On most installations marker beacons are operated. Marker beacons has 3 types; outer marker, middle marker and inner marker.
LLZ : Localizer
The localizer signal provides azimuth, or lateral, information to guide the aircraft to the centerline of the runway.
Glide Slope provides landing slope (elevation information) to aircraft when it comes to reach the touchdown zone of the runway. The standard glide slope for an ILS approach is three degrees downhill to the approach-end of the runway.
Marker (IM : Inner Marker, MM : Middle Marker, OM : Outer Marker)
Marker beacons are used to alert the pilot that an action (e.g., altitude check) is needed. This information is presented to the pilot by audio and visual cues. The ILS may contain three marker beacons: inner, middle and outer. The marker beacons are located at specified intervals along the ILS approach.


Airport surveillance radar (ASR) is a radar system used at airports to detect and display the position of aircraft in the terminal area.
ASDE (Airport Surface Detection Equipment)
Airport Surface Detection Equipment (ASDE) is a traffic management system for the airport surface including runways and taxiways that provides seamless coverage and aircraft identification to air traffic controllers. The system uses a combination of surface movement radar and transponder multilateration sensors to display aircraft position.
ASR (Airport Surveillance Radar)
ASR system consists of two integrated electronic subsystems: primary surveillance radar and secondary surveillance radar. The primary surveillance radar (PSR) uses a continually rotating antenna mounted on a tower to transmit electromagnetic waves that reflect, or backscatter, from the surface of aircraft up to 60 miles from the radar. The radar system measures the time required for a radar echo to return and the direction of the signal and its values are used to measure azimuth and range of aircraft. The secondary radar (SSR) is used to transmit and receive area aircraft data for barometric altitude, identification code, and emergency conditions. The air traffic control uses this system to verify the location of aircraft within a 60-mile radius of the radar site.
ARTS (Automatic Radar Terminal System)
ARTS (Automatic Radar Terminal System) is a system for carrying out air-traffic control in the vicinity of airports which uses both airport surveillance primary and secondary radar and the air-traffic radar beacon system; radar video, representing aircraft targets including flight name, height and speed, Map, etc., and automatically tracks controlled aircraft then presented on the air-traffic controllers' displays.


The TACAN system is a UHF (frequency range of 1025 to 1150 MHz air to ground) omnidirectional navigational aid which provides continuous azimuth information in degrees from the station, and slant range distance information up to 200 NM from the station, dependant on aircraft altitude. TACAN is a system combining the bearing capability of VOR with the distance measuring capability of DME.