GPS – How it works and how to work it.


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GPS – How it works and how to work it.

GPS is revolutionizing navigation

A GPS receiver determines your position by finding your distance from a set of orbiting satellites.

The (~0.1sec) travel time has to measured to exquisite accuracy.

The GPS satellites all transmit on the same two frequencies- L1 & L2.

Digital data is further encoded on the S/V’s signal at a 50Hz frequency.

How accurate is my GPS?

The resulting position accuracy depends on satellite geometry.

Even better accuracy can be obtained by differential GPS

The most basic of GPS’s will tell you your lat/lon.

Match bearing and track to go direct to.

Basic functions are nearest and direct to

On a right downwind for the ILS 29R SCK

Cleared for the approach

On course, heading 291°

Heading 296 tracks the localizer!

GPS and VOR are different!

GPS and VOR are different!

GPS are computer based systems.

In leg mode you fly to the active waypoint from the previous FP fix.

In OBS mode the GPS works more like a VOR.

Here we are tracking outbound on the ECA 071 radial in OBS mode.

IFR GPS installations are more complex than for VFR.

For C129 must have alternate nav available for IFR.

You can substitute your (terminal IFR approved) GPS for ADF or DME

We’re almost at the D9.0 stepdown fix

Airways become long strings of fixes…

A straightforward GPS approach

Missed approaches are never auto-sequenced.

The RNAV (GPS) RWL 8L @ONT has some nuances…

Most waypoints are “fly-by”, allowing for turn anticipation.

The latest approach nomenclature is RNAV (GPS)

The RNAV (GPS) RWY 15 PNN has a TAA

On the RNAV (GPS) Rwy 1 @ BTV procedure turns are required at FOBUX when arriving from the NE.

Some good reading...

Author: Ed Williams