Garmin GNC 420W Pilots Guide - Page 227
FAULT DETECTION AND EXCLUSION, 12.1 Detection and Exclusion
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SECTION 12 - FAULT DETECTION AND EXCLUSION 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. 190-00140-20 Rev. K Oceanic Excluded Satellite Mode (Checkered Pattern) Horizontal Uncertainty Level Figure 12-1 Satellite Status Page GNC 420(A) Pilot's Guide and Reference 12-1
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