Lesson Plans

Teaching and Learning Flying - Airplane Instrument Rating

GPS Navigation and Approach


Global positioning system (GPS) navigation and approach refers to the determination of location, tracking to (and from) and intercepting radials to and from waypoints, including those used in flying GPS instrument approaches, using an approved receiver/processor (e.g., Garmin GNS 530) to receive, interpret and display time and location information from some of a constellation of satellites.


Knowledge and skill in GPS navigation and approaches leads to enhanced positional awareness and safer, more accurate flight.
Safety is enhanced by knowledge and practice with the specific make and model of GPS receiver to be used in flight.
Knowledge and skill in GPS approaches may be used to safely let down in IMC to an increasing number of airports.
Safe GPS approach depends on
    Understanding of GPS equipment and use
    Good communication with ATC
    Proficient AIF while performing precise GPS navigation
Do not rely on GPS altitude information (vertical error can be significant)
Hand-held GPS units may help with situational awareness, but are not approved for IFR navigation.


Instrument Rating PTS (FAA-S-8081-4D)
V.A. Intercepting and tracking navigational systems
To determine that the applicant:
  1. Exhibits adequate knowledge of the elements related to intercepting and tracking navigational systems and DME arcs.
  2. Tunes and correctly identifies the navigation facility.
  3. Sets and correctly orients the course to be intercepted into the course selector or correctly identifies the course on the RMI.
  4. Intercepts the specified course at a predetermined angle, inbound or outbound from a navigational facility.
  5. Maintains the airspeed within +/-10 knots, altitude within +/-100 feet, and selected headings within +/-5°.
  6. Applies proper correction to maintain a course, allowing no more than ¾-scale deflection of the CDI or within +/-10° in case of an RMI.
  7. Determines the aircraft position relative to the navigational facility or from a waypoint in the case of GPS.
  8. Intercepts a DME arc and maintains that arc within +/- 1 nautical mile.
  9. Recognizes navigational receiver or facility failure, and when required reports the failure to ATC.
VI.A. Nonprecision approach
To determine that the applicant:
  1. Exhibits adequate knowledge of the elements related to an instrument approach procedure.
  2. Selects and complies with the appropriate instrument approach procedure to be performed.
  3. Establishes two-way communications with ATC, as appropriate to the phase of flight or approach segment, and uses proper communication phraseology and technique.
  4. Selects, tunes, identifies, and confirms the operational status of navigation equipment to be used for the approach procedure.
  5. Complies with all clearances issued by ATC or the examiner.
  6. Recognizes if any flight instrumentation is inaccurate or inoperative, and takes appropriate action.
  7. Advises ATC or examiner anytime that the aircraft is unable to comply with a clearance.
  8. Establishes the appropriate aircraft configuration and airspeed considering turbulence and wind shear, and completes the aircraft checklist items appropriate to the phase of flight.
  9. Maintains, prior to beginning the final approach segment, attitude within +/-100 feet, heading within +/-10° and allows less than ¾ scale deflection of the CDI or within +/-10° in the case of an RMI, and maintains airspeed within +/-10 knots.
  10. Applies the necessary adjustments to the published MDA and visibility criteria for the aircraft category when required, such as -
      a. NOTAMs.
      b. inoperative aircraft and ground navigation equipment.
      c. inoperative visual aids associated with the landing environment.
      d. NWS reporting factors and criteria.
  11. Establishes a rate of descent and track that will ensure arrival at the MDA prior to reaching the MAP with the aircraft continuously in a position from which a descent to a landing on the intended runway can be made at a normal rate using normal maneuvers.
  12. Allows, while on the final approach segment, no more than a ¾-scale deflection of the CDI or within +/-10° in case of an RMI, and maintains airspeed within +/-10 knots of that desired.
  13. Maintains the MDA, when reached, within +100 feet, -0 feet to the MAP.
  14. Executes the missed approach procedure when the required visual references for the intended runway are not distinctly visible and identifiable at the MAP.
  15. Executes a normal landing from a straight-in or circling approach when instructed by the examiner.
VI. C. Missed approach
To determine that the applicant:
  1. Exhibits adequate knowledge of the elements related to missed approach procedures associated with standard instrument approaches.
  2. Initiates the missed approach promptly by applying power, establishing a climb attitude, and reducing drag in accordance with the aircraft manufacturer's recommendations.
  3. Reports to ATC beginning the missed approach procedure.
  4. Complies with the published or alternate missed approach procedure.
  5. Advises ATC or examiner anytime that the aircraft is unable to comply with a clearance, restriction, or climb gradient.
  6. Follows the recommended checklist items appropriate to the go-around procedure.
  7. Requests, if appropriate, ATC clearance to the alternate airport, clearance limit, or as directed by the examiner.
  8. Maintains the recommended airspeed within +/-10 knots; heading, course, or bearing within +/-10°; and altitude(s) within +/-100 feet during the missed approach procedure.


Encourage mastery of understanding and performance of GPS navigation and approaches to enhance the efficiency and safety of flight
Develop student knowledge and skill in GPS navigation and approaches to meet the Instrument Pilot PTS


    Global Positioning System (GPS)
      1) Definition and description
      2) GPS components
        a) Space elements
        b) Control elements
        c) User elements
          i) Aircraft antennas and receiver/processor (e.g. Garmin GNS 530) that provide position, velocity, and timing information
          ii) Requirements for GPS equipment used under IFR
          • Meet standards in Technical Service Order (TSO) C-129
          • Meet airworthiness installation standards
          • Be "approved" for that type of IFR operation
          • Be operated in accordance with the applicable POH/AFM or supplement
          • Updatable GPS database that supports the appropriate operations
          iii) Equipment approved in accordance with TSO C-115a, VFR and hand-held systems
          • Do not meet TSO C-129 requirements and are not authorized for IFR navigation
          • May only be considered aids to situational awareness
      3) Function of GPS
        a) Operation based on concept of ranging and triangulation from a minimum of four satellites above the mask angle (lowest usable angle above horizon)
        b) Each satellite transmits a specific course/acquisition (CA) code containing
          i) Satellite's ephemeris (exact position in space)
          ii) GPS system time
          iii) Health and accuracy of the data
        c) Pseudo-range (distance determined by time measurement) is derived by receiver/processor
        d) Using pseudo-range and supplied position information from at least four satellites, GPS receiver/processor determines, by triangulation, a three-dimensional position (latitude, longitude, altitude) and time solution
        e) Navigational values are computed by the GPS receiver/processor using the position/time solution above and its built-in database
        f) Receiver autonomous integrity monitoring (RAIM)
          i) Verifies integrity (usability) of GPS signals
          ii) Needs at least five satellites in view (or four plus a barometric altimeter to provide baro-aiding) to detect an integrity anomaly
          iii) Some receivers, with six satellites in view (or five plus baro-aiding) can isolate a corrupt signal and remove it from the navigation solution
          iv) Two types of RAIM messages
          • Not enough satellites available (GNS 530: INTEG annunciation)
          • Potential error detected (GNS 530: WARN annunciation)
          v) Without RAIM, GPS accuracy is not ensured
          vi) Active monitoring of the required alternate means of navigation is not required if GPS receiver uses RAIM
          vii) If loss of RAIM is predicted (see GNS 530 RAIM Prediction), other approved equipment must be used
        GPS RAIM
      4) GPS substitution
        a) IFR certified GPS system may substitute for ADF and DME when
          i) Determining position over DME fix (including operations above FL 240)
          ii) Flying a DME arc (GNS 530)
          iii) Navigating TO/FROM NDB/compass locator
          iv) Determining position over NDB/compass locator
          v) Determining position over fix defined by NDB/compass locator bearing crossing a VOR/LOC course
          vi) Holding over NDB/compass locator
        b) Requirements for using GPS to substitute for ADF or DME
          i) GPS meets airworthiness installation requirements and is operated in accordance with POH/AFM or supplement
          ii) At least en route RAIM or equivalent
          iii) Positions must be retrieved from current database
          iv) Be able to use alternate equipment when RAIM outages are predicted
          v) CDI set to terminal sensitivity (usually 1-1¼ NM) in terminal area
          vi) If alternate airport is required
          • A non-GPS approach must be available at alternate airport
          • If the non-GPS approach requires DME or ADF, aircraft must be equipped with DME or ADF avionics
          viii) Charted ADF and/or DME requirements can be met using GPS, except for use as principal instrument approach navigation source
        c) To determine position over DME fix
          i) Verify satisfactory GPS system integrity
          ii) Select as active GPS waypoint (WP) from GPS database either
          • Five-letter named fix, or
          • Facility establishing DME fix
          iii) Aircraft is over selected 5-letter named fix when GPS indicates aircraft is at active WP
          iv) If facility establishing DME fix selected as WP, aircraft is over fix when on course and GPS distance from WP equals charted DME value
        d) To fly DME arc (GNS 530)
          i) Verify (satisfactory GPS system) integrity
          ii) As active GPS WP, select, from database, facility on which DME arc is based
          iii) Maintain position on arc by reference to GPS distance
        e) To navigate TO or FROM an NDB/compass locator
          i) Verify integrity
          ii) As active WP, select, from database, NDB/compass locator or collocated fix of the same name
          iii) Select and navigate on course to or from WP
        f) To determine position over NDB/compass locator
          i) Verify integrity
          ii) Select NDB/compass locator from database
          iii) Aircraft is over NDB/compass locator when GPS indicates aircraft is at the active WP
        g) To determine position over fix when an NDB/compass locator bearing intersects a VOR/LOC course
          i) Verify integrity
          ii) As active WP, select from database either 5-letter named fix or NDB/compass locator
          iii) Aircraft is over fix when GPS indicates at 5-letter named fix WP, or when GPS bearing to NDB/compass locator WP is the same as that charted for fix as aircraft is flying along prescribed track
        h) To hold over NDB/compass locator
          i) Verify integrity
          ii) Select NDB/compass locator from database as active WP
          iii) Select nonsequencing mode and appropriate course according to POH or supplement
          iv) Hold using GPS according to POH (GNS 530)
      5) IFR flight using GPS
        a) Install, check current database
        b) Conduct operations in accordance with POH (GNS 530)
        c) Study to become comfortable with operation of specific receiver installed in aircraft
        d) Practice in VFR condition first
        e) Check GPS NOTAMs
        f) Obtain GPS RAIM availability information
        g) Check required underlying ground-based navigation facilities and related aircraft equipment operational
        h) Enter flight plan into GPS receiver: departure WP, DP, enroute WPs, STAR, IAF, destination airport (GNS 530)
        i) Select, activate flight plan
        j) GPS provides course guidance between WPs, including desired direct track to WP and aircraft's actual track over ground
      6) GPS instrument approaches (GNS 530)
        a) Types
          i) GPS overlay approaches have "or GPS" as part of the approach name
          ii) GPS stand-alone approaches are named "GPS..." or "RNAV..."
        b) Ground-based NAVAIDs and associated aircraft avionics are not required to be operational or monitored, but monitoring available backup navigation systems is always recommended
        c) Practice GPS IAPs under VMC first until thoroughly proficient
        d) Fly only those IAPs retrieved from current GPS database to assure compliance with published procedures and proper RAIM and CDI sensitivities
        e) Follow manufacturers recommended procedures (GNS 530)
        f) Fly full approach from initial approach WP (IAWP) or feeder fix unless specifically cleared otherwise
        g) Load and arm (activate) IAP beyond 30 NM from airport so receiver will change from enroute CDI (+/- 5 NM) and RAIM (+/- 2 NM) sensitivity to terminal sensitivity (+/- 1 NM) when within 30 NM of airport
        h) Follow manufacturers recommendations for holding pattern (GNS 530) and procedure turn (GNS 530) which may require pilot action to stop and later resume waypoint sequencing
        i) Follow receiver operating manual procedures when receiving vectors to final (GNS 530)
        j) Within 2 NM of final approach WP (FAWP), armed approach mode switches to active approach mode resulting in RAIM and CDI sensitivity changing to approach mode sensitivity, +/- 0.3 NM
        GPS CDI Scale
        k) To help maintain position orientation during CDI sensitivity ramp down
          i) Get established on final approach course beyond 2 NM from FAWP
          ii) Note crosstrack error (compare actual to desired/direct track)
        l) If approach mode is not armed by 2 NM prior to FAWP
          i) Approach mode will not become active at 2 NM from FAWP
          ii) GPS receiver will flag
          iii) Pilot should fly to MAWP and execute a missed approach (GNS 530)
        m) Check approach mode active prior to FAWP
        o) GPS missed approach
          i) Follow manufacturers recommendations (GNS 530)
          ii) Requires pilot action to sequence past MAWP to missed approach procedure
          iii) No turns prior to MAWP
          iv) Additional pilot action required if first tack of missed apporach is via a course rather than direct to next WP
        p) Flying to alternate airport after missed approach
          i) Avionics needed to receive all appropriate ground facilities for route to alternate must be installed and operational
          ii) Altenate airport must have an operational approach that is NOT based on GPS or LORAN C navigation; and aircraft must have the appropriate operational equipment to fly that approach
      7) GPS errors
        a) Whenever less than 24 satellites are operational, GPS navigational capabilities may be lost in certain areas
        b) Loss of signal in valleys surrounded by high terrain
        c) Loss of signal when aircraft's GPS antenna is "shadowed" by aircraft structure (e.g. when the aircraft is banked)
        d) Signal interference
          i) From certain receivers, transceivers, mobile radios, portable receivers; "harmonic interference" from some UHF transmissions
          ii) Isolate interference by moving or turning off suspected devices while monitoring GPS receiver's signal quality data page
        e) Equipment characteristic and geometric factors can cause small errors (typically less than 100 feet)
        f) Small position errors or momentary loss of signal
          i) Small atomic clock inaccuracies
          ii) Receiver/processor error
          iii) Mulitpath (signals reflected from hard objects)
          iv) Ionospheric and tropospheric delays
          v) Satellite data transmission error
        g) Selective availability (SA)
          i) Method by which DOD can create significant clock and ephemeris errors in the satellites
          ii) When SA active
          • Horizontal accuracy is within
              100 m 95% of time
              300 m 99.99% of time
          • Vertical accuracy is within
              156 m 95% of time
              500 m 99.99% of time
          • Time accurate within
              300 nsecs 95% of time
              900 nsecs 99.99% of time
        h) Do not rely on GPS altitude information (vertical error can be significant)
      Demonstrate GPS operation, navigation and approach
      Coach student practice
    • Critique student performance


    • Expired database
    • Incorrect waypoint data entry and confirmation
    • Failure to use proper procedures for course interception and tracking
        Follow proper procedures for the specific unit in order like a checklist
    • Failure to have essential knowledge of the information on the instrument approach chart
        1) Plan ahead
        2) Know approach(es) to expect (ATC, ATIS)
        3) Study, record, memorize key data in advance
          How low? How long? How far? Which way?
        4) Use PC or simulator to practice flying approaches to destinations of upcoming flights
    • Incorrect communications procedures or noncompliance with ATC clearances or instructions
        If cannot comply, request amendment
    • Failure to accomplish checklist items
        1) Start before landing checklist on initial approach segment or on initial vectors for approach
        2) Complete before landing checklist at FAF (gear down)
    • Faulty basic instrument flying technic
        May be due to cockpit disorganization and increased workload
    • Inappropriate descent below the MDA
        1) May indicate inadequate speed of cross-check and interpretation during high workload time
        2) Add 50 foot (or more) buffer above MDA, especially in turbulence

Greg Gordon MD, CFII