Global Positioning System What pilot/students need to know!

GPS Generally The GPS is a U.S. satellite based radio navigational , positioning, and time transfer system operated by the DoD. The system provides highly accurate position and velocity information and precise time on a continuous global basis to properly equipped users.

There are two levels of service Standard Positioning Service (SPS) Precise Positioning Service (PPS)

(SPS) and (PPS) 100 meters-95% 300 meters-99.99% PPS Is more accurate than SPS; however it is limited to authorized U.S. and users who can satisfy specific U.S. requirements

Each satellite transmits specific code It is called a “CA” or Course/Acquisition code. It contains information on the satellites position,GPS system time, clock error and the health and accuracy of the data.

Your Receiver... matches each satellites CA Code with an identical copy of the code contained in the receivers database. By shifting the receivers code its matching the satellite and by comparing this shift with the satellite internal clock...wala!..magic!

Measuring distance The distance derived from this computing is called pseudo-range because it is not a direct measurement but rather, measurement based on time. Your receiver needs to know the satellites exact position in space The receiver does the math to tell you where you are!

There are 24 satellites A minimum of five satellites are always observable by a user anywhere on earth. On December 8, 1993 the FAA granted approval to use GPS to conduct oceanic, domestic enroute, terminal IFR operations, and certain instrument approach procedures, under specified conditions:

General Requirements The GPS equipment must be approved in accordance with TSO C-129. Aircraft using GPS under IFR must be equipped with an alternate means of navigation. Procedures must be established if satellite reception is impaired, i.e.. delay or cancel flight.

...more conditions The GPS flight must must be conducted in accordance with FAA-approved flight manual or flight manual supplement. Aircraft navigating by GPS are considered (by ATC) to be RNAV aircraft. The “/R” on the flight plan tells them that.(GPS goes in remarks) Prior to flight GPS NOTAMS

There are/were three Phases of operations... Phase 1 You can use GPS only if ground-based nav equipment is monitored and operational. Phase II GPS without actively monitoring ground-based nav equipment..avionics must be installed an working..but not turned on. Phase III is where approach plates are titled “GPS” and you do not need other nav’ gear.

References Aeronautical Information Manual (Navigation Aids Chapter 1 Page 1-36) FAA Advisory Circular AC 90-94 “Guidelines for using GPS for IFR...”

Let’s talk about the 3 Phases! Phase 1 ended February 1994 when the FAA declared GPS operational for civil operations. Phase II began February 1994 when the FAA declared the system useable. (Don’t need to actively monitor ground-based as long as something tells you GPS is working.

Phase III Phase III requires modification of the instrument approach procedure name to include “GPS” on the chart. You need neither the traditional avionics nor the ground station navaid(s) to be operational or monitored to fly non precision approach...if RAIM is monitoring the integrity of your GPS System.

What is “RAIM” Receiver Autonomous Integrity Monitoring. Your receiver tells you if you are receiving adequate signal to fly the GPS...if not, delay the flight or cancel as appropriate. The reason being that Phase I,II,& III have additional criteria:

To repeat... GPS must be TSO’d Receiver should have database with airport of choice...and no LOC, LDA or SDF approach. If approach not in database..it is probably unsafe that is why it is not there. GPS should store all waypoints depicted on the approach chart.

...more Approach must be flown in accordance with FAA Aircraft Flight Manual or flight manual supplement. Any required alternate airport should have an approved instrument approach other than GPS...NOTAMS is a pilot responsibility. The GPS overlay approaches are limited to the U.S. national airspace.

and last but not least...! Procedures should be established by the pilot in the event of GPS outages..meaning rely on other equipment, delay departure or discontinue IFR operations.

Pilot Operations To quote AC 90-94, “...All pilots must be thoroughly familiar with GPS equipment installed in the aircraft and its limitations.” The pilot should follow the specific start-up and self-test procedures for the GPS receiver as outlined in the FAA AFM or Flight Manual Supplement.

GPS NOTAMS Request from Briefer Use identifier “GPS”, through the Direct User Access Terminal System (DUATS) ..remember, if the NOTAMS indicate GPS is not working...the approach is not authorized.

Appropriate Approach The pilot must select appropriate approach from GPS receiver to determine RAIM integrity for that approach. If GPS is out amend “/R” flight plan.

How about the alternate? If the GPS ain’t working...the alternate must have an approved approach...other than GPS or..Loran-C!”...which is anticipated to be operational at the estimated time of arrival!” What do you use? ILS, NDB...?

GPS

That’s all Folks!