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Global Positioning System (GPS) (Part Two)

in Navigation Systems

GPS Substitution
IFR En Route and Terminal Operations


GPS systems, certified for IFR en route and terminal operations, may be used as a substitute for ADF and DME receivers when conducting the following operations within the United States NAS.

  1. Determining the aircraft position over a DME fix. This includes en route operations at and above 24,000 feet mean sea level (MSL) (FL 240) when using GPS for navigation.
  2. Flying a DME arc.
  3. Navigating TO/FROM an NDB/compass locator.
  4. Determining the aircraft position over an NDB/compass locator.
  5. Determining the aircraft position over a fix defined by an NDB/compass locator bearing crossing a VOR/LOC course.
  6. Holding over an NDB/compass locator.

GPS Substitution for ADF or DME

Using GPS as a substitute for ADF or DME is subject to the following restrictions:

  1. This equipment must be installed in accordance with appropriate airworthiness installation requirements and operated within the provisions of the applicable POH/AFM, or supplement.
  2. The required integrity for these operations must be provided by at least en route RAIM, or equivalent.
  3. WPs, fixes, intersections, and facility locations to be used for these operations must be retrieved from the GPS airborne database. The database must be current. If the required positions cannot be retrieved from the airborne database, the substitution of GPS for ADF and/or DME is not authorized
  4. Procedures must be established for use when RAIM outages are predicted or occur. This may require the flight to rely on other approved equipment or require the aircraft to be equipped with operational NDB and/or DME receivers. Otherwise, the flight must be rerouted, delayed, canceled, or conducted under VFR.
  5. The CDI must be set to terminal sensitivity (1 NM) when tracking GPS course guidance in the terminal area.
  6. A non-GPS approach procedure must exist at the alternate airport when one is required. If the non-GPS approaches on which the pilot must rely require DME or ADF, the aircraft must be equipped with DME or ADF avionics as appropriate.
  7. Charted requirements for ADF and/or DME can be met using the GPS system, except for use as the principal instrument approach navigation source.

NOTE: The following provides guidance, which is not specific to any particular aircraft GPS system. For specific system guidance, refer to the POH/AFM, or supplement, or contact the system manufacturer.

To Determine Aircraft Position Over a DME Fix:

  1. Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.
  2. If the fix is identified by a five-letter name which is contained in the GPS airborne database, select either the named fix as the active GPS WP or the facility establishing the DME fix as the active GPS WP. When using a facility as the active WP, the only acceptable facility is the DME facility which is charted as the one used to establish the DME fix. If this facility is not in the airborne database, it is not authorized for use.
  3. If the fix is identified by a five-letter name which is not contained in the GPS airborne database, or if the fix is not named, select the facility establishing the DME fix or another named DME fix as the active GPS WP.
  4. When selecting the named fix as the active GPS WP, a pilot is over the fix when the GPS system indicates the active WP.
  5. If selecting the DME providing facility as the active GPS WP, a pilot is over the fix when the GPS distance from the active WP equals the charted DME value, and the aircraft is established on the appropriate bearing or course.

To Fly a DME Arc:

  1. Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.
  2. Select from the airborne database the facility providing the DME arc as the active GPS WP. The only acceptable facility is the DME facility on which the arc is based. If this facility is not in your airborne database, you are not authorized to perform this operation.
  3. Maintain position on the arc by reference to the GPS distance instead of a DME readout.

To Navigate TO or FROM an NDB/Compass Locator:

  1. Verify aircraft GPS system integrity monitoring is functioning properly and indicates satisfactory integrity.
  2. Select the NDB/compass locator facility from the airborne database as the active WP. If the chart depicts the compass locator collocated with a fix of the same name, use of that fix as the active WP in place of the compass locator facility is authorized.
  3. Select and navigate on the appropriate course to or from the active WP.

 

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