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Until recently, pilots operating with GPS receivers certified for instrument flight rules (IFR) were not permitted to use GPS for any approach operations where no GPS overlay or stand-alone approach existed. Furthermore, GPS was not approved for use in any capacity for localizer-type approaches; e.g., ILS, localizer, SDF, or LDA. This forced those equipped with IFR GPS receivers to maintain and replace DME and ADF receivers in order to utilize all approaches in the National Airspace System. GPS has proven itself a reliable and highly accurate navigation system over the past four years, which warranted a change in these policies.
AOPA, working together with the FAA Flight Standards Division, has reached agreement on FAA policy changes that permit IFR-certified GPS receivers to be used in lieu of DME and ADF for most IFR operations (see " Limitations"). This policy fundamentally permits DME and ADF avionics to be removed with little compromise in operational capability. AOPA will continue to work with the FAA to implement GPS approaches at airports served only by an NDB approach.
This fact sheet is intended to clarify and provide guidance on how to take advantage of this new policy.
Effective July 16, 1998, pilots may substitute IFR-certified GPS receivers for DME and ADF avionics for all operations except NDB approaches without a GPS overlay. GPS can be used in lieu of DME and ADF on all localizer-type approaches as well as VOR/DME approaches, including when charted NDB or DME transmitters are temporarily out of service. It also clarifies that IFR GPS satisfies the requirement for DME at and above Flight Level 240 specified in FAR 91.205(e). This approval represents a major step toward removing the need to retain DME or ADF in our cockpits for any reason.
Note: Air carrier operators should consult their operations specifications and their principal operations inspector for approval.
There are still three instances in which DME or ADF are still required.
AOPA is working with the FAA and the manufacturers to have these restrictions removed and will keep you informed.
Note: Pilots should exercise caution when selecting the appropriate DME and NDB/LOM locations to avoid erroneous distance information.
As with most operational capabilities, there are minimum requirements that must be met in order to take advantage of their benefits in a safe manner. When using GPS in lieu of DME and ADF for the purposes stated above:
Caution: Pilots should be extremely careful to ensure that correct distance measurements are used when utilizing this interim method. It is strongly recommended that pilots review distances for stepdown points during preflight preparation. (See Figure B; a GPS receiver set to the FAF, AASON, would be counting up to 8.1 at the missed approach point, where as a DME would have counted down to 0.9 at this same missed approach point.)
Caveat: The FAA offers the following ï¿½ GPS is a supplemental navigation system, in part due to signal availability. There will be times when your system will not receive enough satellites with proper geometry to provide accurate positioning or sufficient integrity. Procedures should be established by the pilot in the event that GPS outages occur. In these situations, the pilot should rely on other approved equipment, radar vectors, delayed departure, rerouting, or discontinuance of IFR operations.
Further guidance will be provided in updated editions of the Aeronautical Information Manual (AIM) and Advisory Circular AC 90-94 titled "Guidelines for using global positioning system equipment for IFR en route and terminal operations and for non-precision instrument approaches in the U.S. National Airspace System."
AOPA members may direct questions to the AOPA Aviation Services Department at 1-800-872-2672.