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• [ejet:gps_sats]

GPS

Overview

System consists 24 satellites orbiting the earth in 6 orbital planes

Principle of operation

Receiver type

On the EMB - 170/190

• the GPS reciever meets the standards of TSO-C129A
• includes barometric aiding
• and RAIM required for TSO standard
• 2 x GPS recievers

• RAIM (Reciever Autonomous Integrity Monitoring)
• Is used to verify the integrity of the signals recieved
• a RAIM warning aadvises the crew that the reciever has detected a problem with a satellite signal
• Without RAIM capability, the crew has NO assurance of the accuaracy of the GPS position
• RAIM must be available before descending below the LSALT / MSA
• RAIM is a simple prediction and does not guarantee that RAIM failure will not occur
• RAIM may be either FD or FDE
• Fault Detectiion (FD)
• Needs at least 5 satellites
• compares positions with each others so a faulty satellite idenified
• Fault Detection and Exclusion (FD&E)
• Needs at least 6 satellites
• detect a faulty satellite and remove it from the Navigation Solution
• will continue excluding faulty satellites til FD is  reached
• Modes of Operation
• Navigation solution with RAIM
• 3D (min 4 satellites) without RAIM
• 2D (min 3 satellites) without RAIM
• Dead reckoning (DR) or loss of nav. solutio
• Barometric Aiding

RNP / EPU

EPU - Estimated Position Uncertainty

• in  NM
• actual position of aircraft being within 0.3 NM for 95% of the flight time
• EPU > RNP for a set period of time generates
• 'unable RNP' on the MCDU
• 'DEGRAD' on the PFD

Approach mode (APPR)

FMS transitions to approach mode when the aircraft is within

• 2 NM of the FAF
• Reciever automatically performs a RAIM prediction for the approach
• APPR will not be entered unless RAIM is predicted to be available for the approach and missed
• No loss of RAIM warning until 5 mins after passing the FAF

See also

GPS RNAV Approach

EMB GPS

Categories: Embraer 170/190 | Flight Instruments/Comm/Nav/FMS