Approach Basics (GX50/60)

En Route RAIM, or a 2.0 nm alarm limit is provided at all other times.

Note that the three different equipment operation states: En route, Approach-Transition, and Approach-Active are somewhat but not directly related to the three RAIM alarm limits of En route, Terminal, and Approach. The equipment states are defined by the CDI sensitivity and operational requirements. When you depart an airport, the equipment is operating En route, but it is providing Terminal RAIM integrity.

How Often Will RAIM Be Unavailable?

RAIM availability depends on many factors, including the number of operational satellites in the sky, the time of day, the location, the receiver design, the antenna mask angle and location, and on the method of baro-aiding. The Apollo GX has been designed such that with an optimal 21 satellites in operation, Approach RAIM availability should exceed 95%. There are currently, at the time this manual was published, at least 24 satellites in operation; however, the Federal Navigation Radio Plan only guarantees that there is at least a 95% probability that 21 will be operational at any given time.

What Is Baro-aiding?

Baro-aiding is used to enhance RAIM availability. It is a method where pressure altitude data can be used to provide RAIM availability during some times when RAIM would not be available using the satellites alone.

What does it mean when I get a “RAIM not available” message?

If RAIM is not available, your Apollo GX may be capable of continuing to provide good accurate IFR navigation. What you have lost is the ability to tell if a satellite is sending bad data. For all operations except Approach, the FAA has determined that it is acceptable for you to continue to use GPS for IFR

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