Section 9: Fde (Fault Detection & Exclusion); Detection And Exclusion - Garmin GNC 420 Pilot's Manual & Reference

Fault Detection & Exclusion
FDE is an acronym that stands for Fault Detection and Exclusion. FDE was incopor-
ated in the Garmin 400 Series 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" per FAA Notice N8110.60. The oceanic
fl ight phase is used by the GNC 420 when you are more than 200 nautical miles from the
nearest airport. There are two main aspects to address in the FDE system. The fi rst
relates to the unit's software side, in regard to detection and exclusion of faulty satellites.
This feature requires no pilot interaction during fl ight. However, the second aspect is that
of predicting the capability of the GPS constellation to provide service during a fl ight.
This is done by the pilot before the fl ight.

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 will exclude one or more failed satellites and
prevent them from being used during navigation. This allows the GPS to return to normal
performance without interruption. The process is entirely automated and does not re-
quire pilot interaction during fl ight. To enhance safety, FDE functionality is provided for
other phases of fl ight (non-precision approach, terminal, en route). The FDE functionality
for non-oceanic fl ight phases adheres to the same missed alert probability, false alert prob-
ability, and failed exclusion probability specifi ed by N8110.60.
Section 9
FDE
Oceanic Mode Excluded Satellite
Annuciation (checkered pattern)
SATELLITE STATUS PAGE
The Satellite Status Page above shows satellite number 9
exclusion during oceanic phase of flight. No message notify-
ing 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.
9
Horizontal Uncertainty Level
149