GPS and INS theory and operating characteristics (Cont)

T-45C TS INav-02

Introduction to INav and Voice Procedures

14. A minimum of three GPS satellites are required for

lat/long positioning; four for lat/long/altitude

NOTE: T-45C requires four satellites for full system

operability; does not compute GPS altitude.

15. GPS equipment used for IFR navigation must be

approved by the FAA [also by DoD for military

aircraft]

16. Aircraft using approved GPS for IFR navigation

must also have an approved operational alternate

means of navigation

17. FAA considers aircraft navigating with GPS to be

Area Navigation (RNAV) capable; flight plans

should be so annotated with the appropriate code

following aircraft type

18. CNO and FAA have not yet (time of this writing)

approved the T-45C for RNAV. CNO only allows

(time of this writing) GPS to support visual

navigation

INS 2.1.10.1.1.1.2

Sg 9, fr 7

Inertial Navigation

THEORY: An inertial navigation system determines

System (INS)

aircraft position by sensing three-dimensional

acceleration vectors, whenever the aircraft moves.

Initial alignment establishes a “level” platform. Initial

geographic (lat/long) position information must be

supplied to the INS if it is to be used for navigation.

The T-45C uses currently sensed GPS position or

waypoint zero (WYPT-0) for that initial position

alignment. Acceleration vectors are derived from

two sources: ring laser gyroscopes, and three axis

(xyz) accelerometer readings

NOTE: The T-45C GPS and INS are linked together

in the Global Positioning System/Inertial Navigation

Assembly (GINA).

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(2-02) Original