GPS Presentation for pilots. Covers basics of GPS such as principles of operation and considerations to keep in mind when using this type of technology for IFR navigation.

1. Global Positioning System (GPS)
Sergio Sovero
ERAU

2. Global Positioning System
• Satellite-based navigation.
• U.S.: Operated and controlled
by the Department of Defense
(DOD)
• NAVSTAR
▫ Comprises 24 satellites
orbiting the Earth.
• Three segmets:
▫ Control
▫ User
▫ Space

3. Control Segment
• Consists of ground reference
stations responsible for:
▫ Checking altitude, position,
speed, and overall integrity of
the satellite constellation.
▫ Atomic clock integrity
• Master Control Station
▫ Located in Colorado Springs,
Colorado.
▫ Responsible for overall
management of the remote
monitoring and transmission
sites.

4. Space Segment
• 32 satellites in total (FAA)
▫ NAVSTAR  24 satellites.
▫ 5 in view at all times
 Typically 7 -12 in view
• Atomic clocks inside the
satellites measure the exact
time at which the signal is
emitted.

5. User
Segment
• GPS receiver equipment
• Examples: our
airplane receivers,
handheld devices
(mobile phones,
iPads, etc.)

6. Pseudo-ranging
• Calculating distance having
time and velocity information.
• GPS signals travel at the
speed of light.
• Receiver determines the time
it took the signal to travel.
• 3 satellites required for 2D
positioning.
• 4 satellites required for 3D
(latitude, longitude, and
altitude)
• Triangulation  intersection
of the spheres is where you
are.

7. Satellite signal
• The signal emitted by each
satellite consist of three main
components:
▫ The ID of the satellite
▫ Satellite position
▫ Emission time

8. Receiver Autonomous Integrity
Monitoring (RAIM)
• Software responsible for checking both signal integrity and
accuracy.
• Alerts the pilot if the signal is not precise enough for IFR
navigation (LOI).
• If a LOI indication is displayed, the usage of GPS should be
discontinued.
• At least 5 satellites required (fault detection only)
▫ 6 satellites will enable RAIM to exclude a faulty satellite
(fault detection + exclusion)

9. • If the receiver is not WAAS equipped, and GPS is going
to be utilized as a primary means of navigation (T-
routes), the pilot must check RAIM for destination
airport.
▫ Also, GPS NOTAMs must be reviewed for possible
outages.
• Databases typically expire every 28 days.
▫ Expire database can still be used only if the pilot
visually cross-checks enroute GPS waypoints with a
current charts.

10. Loss of RAIM = LOI indication
• Receiver conducts a RAIM check 2
nm prior the FAWP.
• If either RAIM UNAVAIL or
ABORT APR  execute missed
approach.
• If RAIM is not available, you will not
be offered GPS approaches when
you attempt to load a procedure.
• If you loaded a procedure when
RAIM was available and then it
became unavailable, the procedure
will not activate.

11. RAIM failures on an IAP
• If the RAIM check prior to the
FAWP fails, the G1000 will not
enter the approach mode.
• Do not descend, fly to the
MAWP and contact ATC.
• Most receivers can operate
without RAIM for 5 minutes to
allow the approach completion
(AIM).
• Regardless of where you are on
the IAP:
▫ LOI = MISSED APPROACH
http://sapt.faa.gov/

12. Wide Area Augmentation System
(WAAS)
• Corrects for signal and propagation errors
• Error reduce from 75 feet to 10 feet (signal augmentation)

13. How does WAAS work?
1. WAAS Geostationary satellites send a signal.
2. WAAS Ground Ref. stations calculate by how much
the signal if off in terms of distance.
3. Each station then sends the corrected message to a
WAAS Master Station.
4. Through an uplink station, the final corrected
signal is sent to the geostationary satellites.
5. Geostationary satellites send improved signal to
WAAS equipped receiver onboard the airplane.

14. Questions