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What's Happening to the Navaids?

by Darren Smith, CFII/MEI
From IFR Checkride Reviewer

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The 2005 Federal Radionavigation Plan was published in February 2006 by the Department of Defense, Department of Homeland Security, and Department of Transportation.  This document can be obtained here.  This annual document describes the government's plan for the navaids we use in aviation.  This 74 page document details the policies and operating plans related to the following radionavigation systems:

Global Positioning System (GPS)

The GPS provides two levels of service: SPS which uses the coarse acquisition (C/A) code on the L1 frequency, and PPS which is restricted to U.S. armed forces.  A second civil signal will be added at the GPS L2 frequency designated as L2C.  A third civil signal will also be added at 1176.45 and designated as L5.  All 24 satellites should be upgraded to L5 capability by 2015 leading to GPS Landing System approaches.

Threats:  The government has determined that GPS services are susceptible to various types of radio frequency interference and further study will be conducted to study the effects to civilian aviation.

Status:  GPS will be the primary Federally provided radionavigation system for the foreseeable future.

Augmentations to GPS

  • Nationwide Differential GPS (NDGPS): The NDGPS provides increased accuracy and integrity of the GPS using land-based reference stations that transmit correction messages.
  • Wide Area Augmentation System (WAAS): The WAAS, a satellite-based augmentation system (SBAS) operated by the FAA, supports aircraft navigation during departure, en route, arrival, and approach operations.  Full LPV should be available in 2008 while GPS Landing System approaches are expected to be available 2015.
  • National Continuously Operating Reference Stations (CORS): The national CORS is a GPS augmentation system managed by NOAA that archives and distributes GPS data for precision positioning.
  • Global Differential GPS (GDGPS): GDGPS is a high accuracy GPS augmentation system, developed by Caltech’s Jet Propulsion Laboratory (JPL), to support the real-time positioning, timing, and determination requirements of NASA’s science mission.

Tactical Air Navigation (TACAN)

TACAN is the military counterpart of VOR/DME. It is an airborne, ground- or shipbased radionavigation system that combines the bearing capability of VOR and the distance-measuring function of DME. The FAA and DoD currently operate approximately 114 “stand-alone” TACAN stations in support of military flight operations within the NAS. The DoD also operates approximately 30 fixed TACAN stations that are located on military installations overseas, and maintains 93 mobile TACANs and 2 mobile VORTACs for worldwide deployment.

Threats: The DoD requirement and use of land-based TACAN will continue until aircraft are properly integrated with GPS.

Future:  Joint Precision Approach and Landing System (JPALS) Technology Development will create a replacement for TACAN approaches.  JPALS is based on local area differential GPS. This system is being developed to meet the DoD’s need for an anti-jam, secure, all-weather Category I/II/III aircraft landing system that will be fully interoperable with planned civil systems.

Instrument Landing System (ILS)

The Instrument Landing System is the predominant system supporting precision approaches in the U.S. The FAA operates 1,275 ILS systems in the NAS of which 225 are localizer only and 115 of which are Category II or Category III systems. In addition, the DoD operates 160 ILS facilities in the U.S.  With the advent of GPS-based precision approach systems, the role of Category I ILS will be reduced and by 2015 the phase out begins.


Loran-C is a stand-alone, hyperbolic radionavigation system that provides horizontal coverage throughout the 48 conterminous states, their coastal areas, and most of Alaska south of the Brooks Range.

Status:  The Government continues to operate the Loran-C system in the short term while evaluating the long-term need for the system.  System is at risk for shutdown in 2007 pending a determination by the Department of Homeland Security.  This evaluation consists of two elements: a determination of the technical capability of a fully modernized and enhanced Loran system, and a cost-benefit analysis of developing and operating an enhanced Loran system.

Microwave Landing System (MLS)

The FAA has terminated the development of the Microwave Landing System and does not anticipate installing additional MLS equipment in the NAS. MLS service is expected to be phased out beginning in 2010.


VOR/DME provides users with a means of air navigation in the NAS. The FAA operates approximately 60 VOR, 405 VOR/DME, and 590 VORTAC stations, plus another 30 DMEs collocated with NDBs. The FAA owns approximately 900 of these facilities; other Federal agencies, states, local governments, and private entities own the rest. Additionally, the DoD operates approximately 15 VOR, 18 VOR/DME, and 24
VORTAC stations, located predominately on military installations in the U.S. and overseas, which are available to all users.

Status:  VOR/DME will continue to provide navigation services for en route through nonprecision approach phases of flight throughout the transition to satellite-based navigation. The FAA plans to install additional low-power DMEs to support ILS precision approaches as recommended by the Commercial Aviation Safety Team.

Threats:  The FAA plans to reduce VOR services provided in the NAS based on the anticipated decrease in use of VOR for en route navigation and instrument approaches.  Phase out begins 2010.  Preliminary analysis indicates that approximately 350 VORs and 300 ILSs could be discontinued, representing a reduction to approximately 70 percent of the current Navaid population.

Aeronautical Nondirectional Radiobeacons (NDB)

NDBs serve as nonprecision approach aids at some airports. They are also used as compass locators, generally collocated with the outer marker of an ILS, and are used as en route navigation aids. The NAS includes more than 1,300 NDBs. About 225 are owned by the FAA and 50 by the DoD; the rest are non-Federal facilities owned predominately by state and municipal authorities.The role of NDBs will be reduced and most will be phased out.

Marker beacons transmit 400 Hz, 1300 Hz, or 3000 Hz tones on a frequency of 75 MHz. Markers, as they are called, provide audible and visual identification of positions along the final approach path of a precision instrument approach.The FAA intends to phase down marker beacons in favor of using published distances to a DME facility.  Phase out began 2005.

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