Garmin GPS 400W Pilot's Manual Addendum - Page 32

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Part Three: Section 1

TAWS Introduction

atmosphere conditions seldom match the standard

conditions deﬁned by the International Standard

Atmosphere model (where pressure, temperature, and

lapse rates have ﬁxed values), it is common for the

Baro-Corrected Altitude (as read from the altimeter) to

differ from the GPS-MSL Altitude.

Premature Descent Alerting (PDA) using GPS-MSL

Altitude

The Premature Descent Alert (PDA) is annunciated

when the aircraft is signiﬁcantly below the

recommended minimum altitude for an approach.

The aircraft' s GPS-MSL altitude is compared to a

calculated Above-Ground-Level (AGL) altitude along

the estimated path to the airport. When the aircraft

descends below the calculated minimum altitude for

the estimated path, the PDA alert is annunciated.

NOTE: The data contained in the TAWS databases

comes from government agencies. Garmin accurately

processes and cross-validates the data, but cannot

guarantee the accuracy and completeness of the data.

TAWS displays terrain and obstructions relative

to the altitude of the aircraft. The displayed alerts

and warnings are advisory in nature only. Individual

obstructions may be shown if available in the database.

However, all obstructions may not be available in the

database and data may be inaccurate. Never use this

information for navigation or to maneuver to avoid

obstacles.

Terrain information is based on terrain elevation

data contained in a database that may contain

inaccuracies. Terrain information should be used

as an aid to situational awareness. Never use it for

navigation or to maneuver to avoid terrain.

TAWS uses terrain and obstacle information sup-

plied by government sources. The data undergoes veri-

ﬁcation by Garmin to conﬁrm accuracy of the content,

per TSO-C151b. However, the displayed information

should never be understood as being all-inclusive.