GPS

 

CFI Instrument Practical Test Standards, FAA-S-8081-9B, June 2001 GPS - FAA  All GPS Approaches are classified as Non-Precision Approach GPS navigation came into being in 1994, it uses satellite networks to create an approach path for a specify runway using waypoints with each point defined by a latitude and longitude. GPS belongs to a family of RNAV - Area Navigation not as expensive as VOR or ILS navigation GPS, IRS, INS, RNP,  is a part of a family of RNAV   RNAV allow an aircraft to fly any course within an area of beacons as apposed to navigating to and from beacons as you would with VOR. There are 4 Types of GPS approaches: LNAV Lateral Navigation       WAAS  (Wide Area Augmentation System) LP   Localizer Performance      WAAS | Baro-Aid GPS Receiver LNAV/VNAV  Lateral Navigation/Vertical Navigation Standard GPS Signal  LPV  Localizer Performance with Vertical Guidance Each type depends on sensitivity and on board equipment and GPS signal availability. You must have enough satellite for RAIM (Receiver Autonomous Integrity Monitoring) and an up to date navigation database  LPV & LNAV /VNAV - provides course guidance on both CDI and glide path indicator  Pilot should follow the glide path to Decision Altitude (DA) LP & LNAV  - only provides lateral guidance and it utilize an Minimum Descent Altitude (MDA) LNAV - Most basic type of approach and does not provide NO Vertical navigation Full Scale deflection from FAF Final Approach Fix to MAF Miss approach point.  Pilot need to determine the proper descent rate to maintain the glide path angle and identify the proper miss approach point.    Use Climb/Descend Table on terminal procedure publication and additional info on the approach chart RNAV to get the appropriate rate of descend for your ground speed LP - Localizer Performance approach is similar to LNAV approach  except the sensitivity increase from Final Approach Fix to Miss Approach Fix. Angular scaling is possible because of WAAS and it increase accuracy of GPS latterly and vertically. LNAV/VNAV  Lateral Navigation/Vertical Navigation The first type of GPS approach with Vertical Guidance, they work with BORO receivers and WAAS receivers to determine if the aircraft is on glide path LPV  Localizer Performance with Vertical Guidance  is the most precise GPS option and is available with WAAS receiver.  II. Technical Subject Areas A. Aircraft Flight Instruments and Navigation Equipment 2. Flight instrument systems and their operating characteristics f. Global Positioning System (GPS) 1) Definition and description a) GPS is a spaced-based positioning, velocity and time system b) Department of Defense (DOD) developed and is responsible for monitoring the GPS satellite constellation to ensure proper operation c) Provides aircraft position referenced to DOD World Geodetic System of 1984 (WGS-84) d) Unaffected by weather e) Meets civil requirements for use as primary means of navigation in oceanic and certain remote areas f) Properly certified GPS equipment is approved for use as supplemental means of IFR navigation for i) Domestic enroute operation ii) Terminal operations iii) Certain IAPs 2) GPS components a) Space elements i) Constellation of 24 Navstar satellites ii) Four satellites in each of 6 orbital planes about 11,000 miles above the earth iii) At least 5 satellites are in view at all times iv) GPS constellation broadcasts pseudorandom code timing signal and data message that aircraft equipment processes to obtain satellite position and status v) Aircraft receiver/processor measures time each signal takes to arrive at receiver and, combining this with location data from each satellite, determines aircraft position b) Control elements i) Network of ground-based GPS monitoring and control stations Five monitoring stations Three ground antennas Master control station ii) Ensure accuracy of satellite positions and clocks 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) Predicting loss of RAIM (other approved equipment must then be used) GNS 530 RAIM Prediction GPS Raim Prediction applet 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 form 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 conditions 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 (GPS)..." 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 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) References: Instrument Flying Handbook, FAA-H-8083-15, 1999 AC 90-94 Guidelines for Using GPS... AIM 1-1-19 GPS NOTAMs GPS PowerPoint Presentation (Washington FSDO) kowoma-GPS