Global Positioning System

(GPS)

US GPS - Operator

US DOD Operates and maintains US GPS

• US DOD- US Department of Defense

• Part of US NAS (Nat’l Airspace System)

US GPS - System

• 24 Satellites in Orbit above Earth

– 10,900 NM orbit above Earth

– 6 orbital planes/flight paths,

– 4 satellites per orbital plane/flight path

– Satellite Orbital Period

• 11 hours and 58 minutes to orbit earth

24 Satellites 6 Orbital Planes

US GPS Configuration

GPS Benefits

All phases of flight

Reliable, accurate positioning

Removal/reduction of costly *GBNAs*GBNA = Ground Based Navigation Aids (VORs, DMEs, etc)

More GPS Benefits• Improves Safety

• Reduces Delays

– Reduce separation minimums

– Improves traffic management

– Expands opportunities to more locations

– Prevents unnecessary reductions in Air Service

How GPS Works• Onboard Computer – measures difference

between Time Signals from 4 or more Satellites– Compares Signal Time against Standard Time

– Uses Time difference to compute Distance (Range), from each Satellite

– Compares Ranges of All Satellites received

– Creates “3-D” LAT-LONG* Position* Latitude-Longitude Position

1

2

3Triangulation

4

Computes Latitude, Longitude, Altitude using Time Differences

RNAV (Area Navigation)

• Method of aircraft navigation for desired

Flight Paths (Preferred Routes)

• Increases airspace capacity

– Permits Direct Routing

– Allows Holding Pattern virtually anywhere

Without RNAV

With RNAV

RNAV Route (Tango Routes) Shown in blue

LPV (Localizer Performance with Vertical guidance)

• Similar to ILS approach

• Need WAAS GPS receiver to execute

• Allows minimums as low as 200 ft AGL

LPV Minimums on Approach Plate

RNP (Required Navigation Performance)

The performance accuracy necessary for

operation within a defined airspace.

RNP 2.0

En Route

2 nm 2 nm

2nm

RNP 1.0

Departure

1nm 1nm

1nm

RNP 0.3

Approach

.3nm .3nm

.3nm

RAIMRAIM - GPS Signal Integrity Monitor

“GPS Fault detection”

• Requires minimum of five visible satellites

• Performs consistency checks of Satellites “in view”

• Assures GPS position accuracy if at least 5 Satellites are “in view” and GPS Receiver is operating normally

RAIM Prediction

4 = To get “3D Image”

+

5th =To detect a fault

+

6th =Isolate and exclude a fault

The End

References• www.faa.gov

• www.gps.gov

• www.skyvector.com

• http://williams.best.vwh.net/waas.pdf

• www.wikipedia.com

• www.skyvector.com

• www.google.com

• www.airnav.com

• And Thanks to Zach Scharbau