Garmin GNC 420(A) Manual

A SERVICE OF

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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 ight 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

ight; predicting the capability of the GPS constellation to

provide service during a ight 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 ight. 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 ight (non-precision

approach, terminal, enroute). The FDE functionality for

non-oceanic ight phases adheres to the same missed alert

probability, false alert probability, and failed exclusion

probability specied by N8110.60.

Figure 12-1 shows satellite number 9 exclusion during

oceanic phase of ight. No message notifying the user

of exclusion appears. In addition to the EPE and DOP

elds, there is the Horizontal Uncertainty Level (HUL)

eld which displays a 99% condence level that the

aircraft position is within a circle with a radius of the value

displayed in the HUL eld.

Oceanic

Mode

Excluded Satellite

(Checkered Pattern)

Horizontal

Uncertainty

Level

Figure 12-1 Satellite Status Page

190-00140-20 Rev. K