BendixKing KLN 89B - Pilots Guide - Manual (Page 233)

receiver, on it’s own, can detect an inaccuracy in the GPS system. It
does this by using distance measurements from as many satellites as
possible to check the consistency of the position (this is called an
over-determined position solution).
If there are not enough satellites in view to assure the position integri-
ty, the KLN 89(B) notifies the pilot. Five measurements with good
geometry (relative positions of the satellites) are needed to provide
RAIM. This means that at least five satellites or four satellites and a
pressure altitude input from the aircraft’s altimeter are required to
assure RAIM availability. Likewise, if this check shows some incon-
sistency in the position, the KLN 89(B) notifies the user that other
navigation sources should be used to cross-check the position.
Additionally, sometimes the receiver is unable to assure the position
to enough accuracy for the phase of flight, due to the location of the
satellites at that instant.
RAIM availability is very seldom a difficulty when in the en route and
terminal phases of navigation. The allowable limits are much tighter
when a non-precision approach is performed with a KLN 89B. For
this reason, the KLN 89B Other (OTH) 3 page allows the pilot to enter
a time and location, and the GPS receiver will predict if RAIM will be
available to shoot the non-precision approach. See section 5.1.9 for
more information about the RAIM prediction capability.
GPS XPRESS™ CARD 8-CHANNEL RECEIVER
The KLN 89 and KLN 89B use an Honeywell GPS receiver known as
the GPS Xpress™ card. It was dubbed this way because it is identi-
cal in size to an everyday credit card, and its faster acquisition time
than previous single-channel designs. The GPS receiver has eight
parallel channels, which means each channel can continuously track
a satellite, for continuous tracking of up to eight GPS satellites. The
parallel receiver design has several advantages:
• Excellent performance during high dynamic conditions (high
velocity and/or acceleration).
• Improved position acquisition time (also known as time-to-first-
fix) over single-channel designs.
• Improved position accuracy.
• The ability of the GPS receiver to perform the RAIM calcula-
tions is enhanced without degrading position tracking.
Appendix F
F-4
GPS Primer Appendix F