Global positioning system Purpose

The global positioning system (GPS) uses navigation satellites to supply airplane position to airplane systems and to the flight crew.

Abbreviations and Acronyms

• ADIRU - air data inertial reference unit

• AMP - amplifier

• APU - auxiliary power unit

• ARINC - Aeronautical Radio, Inc.

• ATT - attitude

• A/D - analog to digital

• BITE - built-in test equipment

• CDU - control display unit

• CONV - convertor

• dc - direct current

• DET - detection

• D/A - digital to analog

• ELEC - electrical

• flt - flight

• FMC - flight management computer

• GP - general purpose

• GPS - global positioning system

• HEX - hexadecimal

• IRS - inertial reference system

• L - left

• LBL - left buttock line

• MMR - multi mode receiver

• nav - navigation

• NCD - no computed data

• NVM - non volatile memory

• ovht - overheat

• pos - position

• PPS - precision positioning service

• R - right

• RAIM - receiver autonomous integrity monitor

• RBL - right buttock line

• rcvr - receiver

• RF - radio frequency

• SAT - satellite

• SCR - silicon controlled rectifier

• SPS - standard positioning service

• SS - single shot

• sta - station

• UTC - universal time (coordinated)

• ΔtBIAS - clock bias

• V - volts

• WL - water line

GPS - GENERAL DESCRIPTION

General

The global positioning system (GPS) calculates this data:

• Latitude

• Longitude

• Altitude

• Accurate time

• Ground speed.

There are two GPS systems. Antenna 1 receives satellite signals and sends them to multi mode receiver (MMR) 1. Antenna 2 connects to MMR 2. The MMRs calculate the airplane position and accurate time. This data goes to the flight management computer system (FMCS) and the IRS master caution unit. The FMCS uses GPS or navigation radio position with inertial reference data to calculate the airplane position. The ADIRU sends position data to the MMRs.

The IRS master caution unit gets GPS data from both MMRs. It causes the GPS fail light on the IRS mode select unit to come on when the two units have a failure or if one unit fails and the master caution annunciator is pushed.

The ground proximity warning computer gets GPS position and velocity data from the MMRs.

The clock gets GPS time and date from the MMRs.

General

These are the components in the flight compartment that have a relation to the GPS:

• Control display units

• Master caution annunciator

• Master caution lights

• IRS master caution unit

• Annunciation and dimming module

• IRS mode select unit.

GPS - FLIGHT COMPARTMENT COMPONENT LOCATION

GPS - COMPONENT LOCATION

General

GPS sensor units are in the multi mode receivers (MMR). The MMRs are in the electronic equipment compartment. MMR 1 is on the E1-2 shelf. MMR 2 is on the E1-4 shelf.

GPS - COMPONENT LOCATION

General

The GPS antennas are on the top of the fuselage.

GPS – INTERFACES

Power and Antenna Interface

Each multi-mode receiver (MMR) has a circuit breaker. The 115v ac buses supply power to the MMRs.

Each MMR receives a radio frequency (RF) signal from a GPS antenna.

Adiru Data Buses

The MMRs get inertial reference data from the ADIRUs. Each MMR receives IR data from its onside ADIRU and the offside ADIRU. During normal operation, MMR 1 uses L ADIRU data and MMR 2 uses R ADIRU data. If there is a loss of data from an ADIRU, the MMR will use the data from the offside ADIRU. The MMRs use this data for system initialization and to help system operation during periods of low satellite coverage.