Navaid

Navaid System provides guidance information or position data for the efficient and safe operation of aircraft supported by one or more radio navigation aids. This Navigational Aid (NAVAID) data is provided as a geospatial vector file formats. It is comprised of one or more NAVAID Components. The Navaid System information is published every eight weeks by the U.S. Department of Transportation, Federal Aviation Administration-Aeronautical Information Services. Navaids are coded in Navigation database(NDB) per ARINC 424, divided into two categories - NDB and VHF.


Before introducing different types of Navaids and its code format in ARINC 424, let’s just have some fun by checking out some Navaids/Airport data (like lat/lot, frequency, etc):

Airport Information(AirNav data)

Identifier, name or city:
Example: KPHX or PHX or VAN NUYS

Navaid Information(AirNav data)

Enter the navaid identifier, name or frequency:
Example: JFK or KENNEDY or 115.9 or 353

Airport and Navaid Information(World Aero Data)


Airports Navaids


NDB

A non-directional (radio) beacon (NDB) is a radio transmitter at a known location, used as an aviation or marine navigational aid. As the name implies, the signal transmitted does not include inherent directional information, in contrast to other navigational aids such as low frequency radio range, VHF omnidirectional range (VOR) and TACAN. NDB signals follow the curvature of the Earth, so they can be received at much greater distances at lower altitudes, a major advantage over VOR. However, NDB signals are also affected more by atmospheric conditions, mountainous terrain, coastal refraction and electrical storms, particularly at long range.

NDBs used for aviation are standardised by ICAO Annex 10 which specifies that NDBs be operated on a frequency between 190 kHz and 1750 kHz, although normally all NDBs in North America operate between 190 kHz and 535 kHz.[1] Each NDB is identified by a one, two, or three-letter Morse code callsign. In Canada, privately owned NDB identifiers consist of one letter and one number. North American NDBs are categorized by power output, with low power rated at less than 50 watts, medium from 50 W to 2,000 W and high being over 2,000 W.

There are four types of non-directional beacons in the aeronautical navigation service:

  • En route NDBs, used to mark airways
  • Approach NDBs
  • Localizer beacons
  • Locator beacons

The last two types are used in conjunction with an Instrument Landing System (ILS).

DME

Distance measuring equipment (DME) is a radio navigation technology that measures the slant range (distance) between an aircraft and a ground station by timing the propagation delay of radio signals in the frequency band between 960 and 1215 megahertz (MHz). Line-of-visibility between the aircraft and ground station is required. An interrogator (airborne) initiates an exchange by transmitting a pulse pair, on an assigned ‘channel’, to the transponder ground station. The channel assignment specifies the carrier frequency and the spacing between the pulses. After a known delay, the transponder replies by transmitting a pulse pair on a frequency that is offset from the interrogation frequency by 63 MHz and having specified separation.

DME systems are used worldwide; their standards are set forth by the International Civil Aviation Organization (ICAO), RTCA, the European Union Aviation Safety Agency (EASA) and other bodies. Some countries require that aircraft operating under instrument flight rules (IFR) be equipped with a DME interrogator. In some other countries, a DME interrogator is only required for conducting certain operations.

While stand-alone DME transponders are permitted, DME transponders are usually paired with an azimuth guidance system to provide aircraft with a two-dimensional navigation capability. A common combination is a DME colocated with a VOR (VHF Omnidirectional Range) transmitter in a single ground station. When this occurs, the frequencies of the VOR and DME equipment are paired. Such a configuration enables an aircraft to determine its azimuth angle and distance from the station. A VORTAC (VOR and TACAN) installation provides the same capabilities to civil aircraft but also provides 2-D navigation capabilities to military aircraft.

Low-power DME transponders are also associated with some ILS (Instrument Landing System), ILS localizer and MLS (Microwave Landing System) installations. In those situations, the DME transponder frequency/pulse spacing is also paired with the ILS, LOC or MLS frequency.

VOR

Very High Frequency (VHF) Omni-Directional Range (VOR) is a type of short-range radio navigation system for aircraft, enabling aircraft with a receiving unit to determine its position and stay on course by receiving radio signals transmitted by a network of fixed ground radio beacons. It uses frequencies in the very high frequency (VHF) band from 108.00 to 117.95 MHz. Developed in the United States beginning in 1937 and deployed by 1946, VOR is the standard air navigational system in the world, used by both commercial and general aviation. By 2000 there were about 3,000 VOR stations around the world including 1,033 in the US, reduced to 967 by 2013 with more stations being decommissioned with the widespread adoption of GPS.

A VOR ground station sends out an omnidirectional master signal, and a highly directional second signal is propagated by a phased antenna array and rotates clockwise in space 30 times a second. This signal is timed so that its phase (compared to the master) varies as the secondary signal rotates, and this phase difference is the same as the angular direction of the ‘spinning’ signal (so that when the signal is being sent 90 degrees clockwise from north, the signal is 90 degrees out of phase with the master). By comparing the phase of the secondary signal with the master, the angle (bearing) to the aircraft from the station can be determined. This line of position is called the “radial” from the VOR. The intersection of radials from two different VOR stations can be used to fix the position of the aircraft, as in earlier radio direction finding (RDF) systems.

VOR stations are fairly short range: the signals are line of sight between transmitter and receiver and are useful for up to 200 miles. Each station broadcasts a VHF radio composite signal including the navigation signal, station’s identifier and voice, if so equipped. The navigation signal allows the airborne receiving equipment to determine a bearing from the station to the aircraft (direction from the VOR station in relation to Magnetic North). The station’s identifier is typically a three-letter string in Morse code. The voice signal, if used, is usually the station name, in-flight recorded advisories, or live flight service broadcasts. At some locations, this voice signal is a continuous recorded broadcast of Hazardous Inflight Weather Advisory Service or HIWAS.


VHF NAVAID Primary Records

Column Field Name (Length)
1 Record Type (1)
2 thru 4 Customer/Area Code (3)
5 Section Code (1)
6 Subsection Code (1)
7 thru 10 Airport ICAO Identifier (4)
11 thru 12 ICAO Code (2)
13 Blank (Spacing) (1)
14 thru 17 VOR Identifier (4)
18 thru 19 Blank (Spacing) (2)
20 thru 21 ICAO Code (2)
22 Continuation Record No. (1)
23 thru 27 VOR Frequency (5)
28 thru 32 NAVAID Class (5)
33 thru 41 VOR Latitude (9)
42 thru 51 VOR Longitude (10)
52 thru 55 DME Ident (4)
56 thru 64 DME Latitude (9)
65 thru 74 DME Longitude (10)
75 thru 79 Station Declination (5)
80 thru 84 DME Elevation (5)
85 Figure of Merit (1)
86 thru 87 ILS/DME Bias (2)
88 thru 90 Frequency Protection (3)
91 thru 93 Datum Code (3)
94 thru 123 VOR Name (30)
124 thru 128 File Record No. (5)
129 thru 132 Cycle Date (4)

NDB NAVAID Primary Records

Columns Field Name (Length)
1 Record Type (1)
2 thru 4 Customer/Area Code (3)
5 Section Code (1)
6 Subsection Code (1)
7 thru 10 Airport ICAO Identifier (4)
11 thru 12 ICAO Code (2)
13 Blank (Spacing) (1)
14 thru 17 NDB Identifier (4)
18 thru 19 Blank (Spacing) (2)
20 thru 21 ICAO Code (2)
22 Continuation Record No. (1)
23 thru 27 NDB Frequency (5)
28 thru 32 NDB Class (5)
33 thru 41 NDB Latitude (9)
42 thru 51 NDB Longitude (10)
52 thru 74 Blank (Spacing) (23)
75 thru 79 Magnetic Variation (5)
80 thru 85 Blank (Spacing) (6)
86 thru 90 Reserved (Expansion) (5)
91 thru 93 Datum Code (3)
94 thru 123 NDB Name (30)
124 thru 128 File Record No. (5)
129 thru 132 Cycle Data (4)