Garmin GTX 330 Manual

A SERVICE OF

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32

Part Three: Section 1

TAWS Operation

Section 2: TAWS Operation

TAWS Alerting

TAWS uses information provided from the GPS

receivertoprovideahorizontalpositionandaltitude.

GPS altitude is derived from satellite measurements.

GPSaltitudeisconvertedtoameansealevel(MSL)-

basedaltitude(GPS-MSLaltitude)andisusedto

determineTAWSalerts.GPS-MSLaltitudeaccuracyis

affected by factors such as satellite geometry, but it is

notsubjecttovariationsinpressureandtemperature

that normally affect pressure altitude devices. GPS-

MSLaltitudedoesnotrequirelocalaltimetersettings

todetermineMSLaltitude.Therefore,GPSaltitude

providesahighlyaccurateandreliableMSLaltitude

source to calculate terrain and obstacle alerts.

TAWS utilizes terrain and obstacle databases that

arereferencedtomeansealevel(MSL).UsingtheGPS

positionandGPS-MSLaltitude,TAWSdisplaysa2-D

picture of the surrounding terrain and obstacles relative

tothepositionandaltitudeoftheaircraft.Furthermore,

the GPS position and GPS-MSL altitude are used to

calculate and “predict” the aircraft’s ight path in

relation to the surrounding terrain and obstacles. In this

manner, TAWS can provide advanced alerts of predicted

dangerousterrainconditions.Detailedalertmodesare

described later in this section.

Baro-Corrected Altitude

Baro-correctedaltitude(orindicatedaltitude)isde-

rivedbyadjustingthealtimetersettingforlocalatmo-

spheric conditions. The most accurate baro-corrected

altitude can be achieved by frequently updating the

altimeter setting to the nearest reporting station along

theightpath.However,becauseactualatmosphere

conditions seldom match the standard conditions

deﬁned by the International Standard Atmosphere

(ISA) model (where pressure, temperature, and lapse

rateshavexedvalues),itiscommonforthebaro-cor-

rected altitude (as read from the altimeter) to differ

fromtheGPS-MSLaltitude.Thisvariationresultsin

the aircraft’s true altitude differing from the baro-cor-

rected altitude.

Power Up

Duringpower-upofthe500WSeriesunit,the

terrain/obstacle database versions are displayed along

with a disclaimer to the pilot. At the same time,

TAWS self-test begins. TAWS gives the following aural

messages upon test completion:

•“TAWS System Test, OK”, if the system passes the test

•“TAWS System Failure”, if the system fails the test

A test failure is also annunciated for TAWS, as

shown in the TAWS Alert Summary table.

TAWS Page

The TAWS Page is in the NAV group of pages (see

the500WSeriesPilot’sGuidefordetailedinformation

regarding page groups and pages).

The TAWS Page

190-00356-30 Rev F