Mmr Data Output Bus

The MMR sends out this data:

• GPS latitude

• GPS latitude Fine

• GPS longitude

• GPS longitude fine

• Clock time and date

• GPS status

• Horizontal figure of merit

• Horizontal integrity limit.

The MMR sends the data to these units:

• FMC 1

• FMC 2

• Clocks, captain and first officer

• Ground proximity warnining computer (GPWC)

• IRS master caution unit.

Flight Management Computer (FMC)

The MMRs send these GPS parameters to the FMC:

• Latitude

• Longitude

• Time

• Horizontal figure of merit

• Horizontal integrity limit.

The FMC uses the data for FMC position update and actual navigation performance (ANP) calculation.

Clock

The clock uses GPS time and date.

Ground Proximity Warning Computer

The MMRs send these GPS parameters to the ground proximity warning computer:

• Latitude (coarse)

• Longitude (coarse)

• Latitude (fine)

• Longitude (fine)

• Ground speed

• True track

• Altitude

• Vertical velocity

• Horizontal dilution of precision (HDOP)

• Vertical dilution of precision (VDOP)

• Horizontal figure of merit (HFOM)

• Vertical figure of merit (VFOM)

• Date

• Time (UTC)

• Horizontal integrity limit (HIL)

• Sensor status.

Latitude and longitude (coarse and fine) information gives airplane position for the TCF and terrain awareness functions. Ground speed, true track, altitude, and vertical velocity are used in the terrain awareness function.

Horizontal dilution of precision, vertical dilution of precision, horizontal figure of merit and vertical figure of merit information are used for airplane position accuracy calculations.

Date and time information is used in the fault monitor process, which labels each fault with the date and time of occurrence. The horizontal integrity limit is used to determine the current integrity limit and GPS non-isolatable satellite failures.

Sensor status lets the GPWC monitor the status of the GPS receiver.

IRS Master Caution Unit

The IRS master caution unit monitors data from the MMRs.

SDI Program Pins

Three program pins tell the MMR if it is number 1 or 2.

GPS - RECEIVER

Purpose

The multi-mode receiver (MMR) contains the GPS receiver. The GPS receiver receives navigation satellite signals to calculate GPS data.

Physical Description

The MMR is a standard ARINC 600 3 MCU unit 3.6 inches wide, 7.9 inches high, and 14.6 inches long. It has passive cooling. The MMR weighs 10 pounds and uses 115v ac, 400Hz power for operation.

GPS ANTENNA

The GPS antennas receive L-band frequency signals (1575.42 MHz) and sends them to the multi mode receivers (MMR). Each antenna contains an integrated preamplifier to increase the signal level to the MMR. The antenna preamplifiers use 12v dc which comes from the power supply in the MMR.

GPS - THEORY OF OPERATION – 1

GPS Segments

The GPS has these three segments:

• Satellite

• User

• Control.

Satellite Segment

The satellite segment is a group of satellites that orbit 10,900 nautical miles above the earth. Each satellite makes an orbit once every 12 hours. There are 21 operational satellites and 3 spares.

The satellites continuously transmit radio signals with

navigation data, range code, and the exact time.

User Segment

The user segment is the GPS receiver unit on the airplane. It receives the satellite signals. The GPS uses the satellite data to calculate the airplane position.

Control Segment

The control segment has control and monitor stations on earth that continuously monitor and track the satellites. The control segment does these things:

• Monitor and correct satellite orbits and clocks

• Calculate and format a satellite navigation message. This message has up-to-date descriptions of the satellites future positions, and a collection of the latest data on all GPS satellites

• Update the satellite navigation message regularly.

The control segment has one master control station and five monitor stations. Three of the monitor stations are also upload stations.

The master control station is in Colorado Springs, USA. The master control station is the operational center of the GPS. The master control station controls all operations in the control segment. The master control station has an atomic clock, this clock is the reference for the GPS.

The monitor stations track the satellites 24 hours a day. The master control station remotely controls the monitor stations through on-line connections. The monitor stations are in these locations:

• Ascension island

• Colorado Springs

• Diego Garcia island

• Hawaii

• Kwajalein island.

The monitor stations receive the same information from the satellites that the GPS receiver unit in the airplane receives.

The monitor stations do these things:

• Record the accuracy of the satellite clocks

• Collect and relay to the control station meteorologic data such as barometric pressure, temperature, and dew point.

The master control station uses this data to calculate the

tropospheric signal delay

• Continuously measure the ranges to all visible satellites. The master control station uses this data to calculate and predict the satellites orbits.

The master control station uses the upload stations to send this data:

• Orbit correction commands to the satellites. The satellites use control rockets to correct their orbits

• The navigation message to the satellites.

The upload stations are on Ascension island, Diego Garcia island, and Kwajalein island.