Garmin GNC 420 - Manual (Page 227)

GNC 420(A) Pilot’s Guide and Reference
SECTION 12 – FAULT DETECTION
AND EXCLUSION
12-1
SECTION 12: FAULT DETECTION
AND EXCLUSION
Fault Detection and Exclusion (FDE) is incorporated in
the Garmin GNC 420 main and GPS software version 3.00
and higher. FDE algorithms provide a basis for approval
per the requirements for “GPS as a Primary Means of
Navigation for Oceanic/Remote Operations”, FAA Notice
N8110.60. The oceanic flight phase is used by the GNC
420 when the aircraft is more than 200 nm from the
nearest airport. FDE requires no pilot interaction during
flight; predicting the capability of the GPS constellation to
provide service during a flight is done by the pilot prior
to departure.
12.1 DETECTION AND EXCLUSION
FDE consists of two distinct parts, fault detection
and fault exclusion. The detection function refers to
the capability to detect a satellite failure which can affect
navigation. Upon detection, the exclusion function
excludes one or more failed satellites and prevents them
from being used during navigation. This allows the
GPS receiver to return to normal performance without
interruption. The process is entirely automated and does
not require pilot interaction during flight. On the Satellite
Status Page, the pilot can view information related to
FDE operation. To enhance safety, FDE functionality
is provided for other phases of flight (non-precision
approach, terminal, enroute). The FDE functionality for
non-oceanic flight phases adheres to the same missed alert
probability, false alert probability, and failed exclusion
probability specified by N8110.60.
Figure 12-1 shows satellite number 9 exclusion during
oceanic phase of flight. No message notifying the user
of exclusion appears. In addition to the EPE and DOP
fields, there is the Horizontal Uncertainty Level (HUL)
field which displays a 99% confidence level that the
aircraft position is within a circle with a radius of the value
displayed in the HUL field.
Oceanic
Mode
Excluded Satellite
(Checkered Pattern)
Horizontal
Uncertainty
Level
Figure 12-1 Satellite Status Page
190-00140-20 Rev. K