A Complete Manual for Conducting International Flight Operations

RAIM Check

RAIM Check

RAIM stands for random autonomous integrity monitoring and is a technology used to assess the integrity of the GPS system. For flight crewmembers operating in Class II navigation it is even more important to evaluate the performance of the GPS system and its availability throughout the flight when no other backups other than IRS will be available. RAIM requires a minimum of 5 satellites. Newer GPS systems have fault detection and exclusion or FDE. The advantage of FDE is that the GPS system using FDE will automatically detect satellite failures and exclude them from the navigation solution. Fault detection and exclusion utilizes an extra satellite to perform FDE predictive checks, so a total of 6 satellites are required.  Satellite availability will be better at higher latitudes rather than mid-latitudes due to the GPS constellations orbit.

Methods for Ensuring RAIM Availability

Crewmembers have several different methods available to ensure that RAIM is available during a flight in Class II airspace. All crewmembers shall use one of the following procedures for conducting a RAIM check prior to flight in Class II navigation.



The first method of RAIM prediction is available from flight planning providers such as GDC or Fltplan.com. Assuming that the correct time has been selected when the flight plan is created it will determine that RAIM is available for the duration of the flight.

The next method of determining RAIM is performed by selecting the RAIM check in the FMS. IF the aircraft is not in motion an estimated time at the destination must be inputted into the FMS. In the Honeywell system the RAIM page is accessed by going to the NAV Page, Position Sensors Page and selecting the Status of the GPS and pressing the RAIM prediction for the representative GPS system.


Revision date: July 29, 2015

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