Specifications

8 | Operation
Receiver Autonomous Integrity
Monitoring (RAIM)
RAIM is a special software algorithm in the MX525A
program which provides another layer of safety because
it gives the operator an alarm indication if the GPS
system accuracy exceeds a predefined tolerance. This
feature requires at least five or more GPS satellites to
operate properly. If the position solution falls outside this
tolerance (usually 100 meter) a “RAIM Unsafe” alarm
will be activated in the MX420 CDU. This means that the
accuracy of the position can not be guaranteed at that
point in time. The operator is advised to use the GPS
for navigation with caution until the RAIM indicator goes
back to safe mode (R+).
The RAIM availability is dependent on the number of
usable satellites in view. Planned outage of satellites
due to maintenance or when certain satellites reach their
age of maturity may cause any of the GPS satellites to
become unusable. If less than 5 satellites are available
a “RAIM Caution” (R?) icon will be displayed. If the
GPS system error exceeds 100 meters “RAIM Unsafe”
(R-) icon will be displayed. The operator should take
cautionary measures during this mode.