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

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


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

COMMON ERRORS

• 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

14 CFR parts 61, 91
AIM
Instrument Flying Handbook FAA-H-8083-15
IAPs (TPPs)
VFR GPS - GNS 430/530 Minicourse (AOPA)
GNS 430/530 PDF Reference Guide (AOPA)

Front Page Top