Part 3: GPS – Use of GPS for IFR operations

This section covers the basic requirements and understanding of use of GPS for IFR operations. For detailed and technical equipment requirements please refer ICAO and state regulatory documents. The content here forth in this section is written from pilot’s point of view and it is assumed that reader has basis knowledge of GPS system.

Use of GPS for IFR operations:

  • prior to use of GPS for IFR operations, NOTAMs and aeronautical information must be reviewed
  • onboard navigation data must be current and appropriate for intended operations
  • approach procedures to be flown must be retrievable from current airborne navigation database supplied by equipment manufacturer
  • system must be able to retrieve the procedure by name from database rather than pilot entering entering series of waypoints manually
  • always determine the date of database issuance and validity before every flight
  • there is no requirement to check each waypoint’s latitude and longitude, type of waypoint and/or altitude constraint, only general relationship of waypoints in procedure is required to be checked
  • for commercial operations, second navigation system for contingency should be available
  • for purpose of satisfying requirement of two independent navigation system, if primary navigation is GPS based, the second system must be independent of GPS (example: VOR or DME/DME/IRU)
  • conduct of GPS IFR operations in oceanic areas is allowed only when approached avionics systems are installed. For example: TSO-C196() users and TSO-C129() GPS users authorized for Class A1, A2, B1, B2, C1, or C2 operations
  • GPS satellite outages are issued as GPS NOTAMs both domestically and internationally, but these effect cannot be determined unless RAIM availability has been checked
  • GPS receivers navigate from one defined point to another which can be way points and computer navigation fix
Waypoints Computer Navigation Fix
  • Waypoint is letter pronounceable fix defined in space by latitude and longitude geographic coordinate
  • ATC units maintain waypoints in their database and use them for air traffic control purpose
  • Waypoints are published on various charts and are ICAO recognized for world wide adoption
  • Computer Navigation Fix (CNF), like waypoint is defined by latitude and longitude geographic coordinate but are not pronounceable
  • ATC doesn’t maintain CNFs in their database and also not use them for air traffic control purpose
  • CNF concept has not yet been recognized by ICAO
  • GPS receiver uses CNFs in conjunction with waypoints to navigate from point to point
  • All CNFs begin with letters “CF” followed by three consonants (example: CFXBG)

ICAO Approach Classifications

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