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Flashcards in GPWS Deck (25):


Newer version and is able to predict terrain ahead using a 3D database

Older versions could only see directly below using RA


A/c requiring a class A TAWS

Req for turbine powered a/c with a TOM of more than 5,700kg and can carry more than 9 PAX


A/c requiring a class B TAWS

Piston a/c with a TOM of more than 5700kg and carries more than 9 PAX


Basic inputs to the TAWS

Radio altimeter
A/c configuration
ILS/MLS - g/s deviation

EGPWS - req a terrain database for looking ahead


When is the TAWS system active

Between 50ft and 2450ft


When can you use the self test on the TAWS

Can be tested in the ground or in the air above 1,000ft


What can you inhibit manually from the TAWS

Gear/flap inhibit - “too low flap/gear” when deliberately l/d in a non standard config

Terrain inhibit - inhibits the terrain look ahead function - for tricky approaches which require flying close to terrain


Different warnings/ alerts

Alert is a caution which is preceded by a warning which requires immediate crew response

Genuine - the GPWS provides a warning in accordance with the technical system
Nuisance - as above but pilot flying does no action as they accept a safe procedure
False - the system has malfunctioned and gives a false warning


What should you do with every GPWS warning

Report it to the aviation authority using a GPWS form


Mode 1 - TAWS

Excessive barometric descent rate

Take into account baro and Radio altimeter to measure rod

Alert = “sink rate, sink rate” - repeated every 1.5 secs
Warning = “pull up”


Mode 2 - TAWS

Excessive terrain closure

Inputs - Rod, rad alt, airspeed

Alert = “terrain terrain” - initial penetration area

Warning = “pull up” - inner boundary


Mode 2a - TAWS

Flaps not in l/d config

Upper limit = speeds less than 220kts and 1650ft

When the a/c speed increases over 220kts - warning boundaries expand to 2450ft


Mode 2b - TAWS

Flaps in the l/d config

Operates up to 789ft and if the rate of closure is 3000fpm or greater


Mode 3 TAWS

Height loss after T/o or GA

Inputs - Baro, rad alt, a/c config

Armed between 30 - 700ft but wont arm until 200 ft on the aprch
Alert = “Don’t sink”
Warning = “Pull up” - when height loss = or exceeds 10% of the RA


Mode 4 TAWS

Unsafe terrain clearance

Inputs - Baro, rad alt, a/c config, airspeed


Mode 4a TAWS

Unsafe terrain clearance - gear retracted

Armed when passing 700ft

Alert = “Terrain, terrain”

Warning = “Too low gear” - below 500ft and a speed of less than 190kts - when the a/c is sped up to over 190kts - warning threshold increases to 1000ft


Mode 4b TAWS

Unsafe terrain clearance - gear extended

Below 159kts and 245ft = “Too low, flaps”

Above 159kts and between 245 to 1000ft = “Too low, terrain”

Warning = “Pull up”



EGPWS generates a Terrain clearance floor around the active r/y, longer than 3500ft using a terrain database

Function of the rad alt and position with respect to the r/y regardless of a/c config

Outer limit - up to 700ft


Mode 5 TAWS

Excessive descent below g/s

Armed when the g/s signal is received from the captains ILS receiver and the a.c is at or below 1000ft

Soft alert - below 1000ft + 1.3 dots deviation = “Glideslope, Glideslope”

Hard alert - below 300ft - 2 dots deviation = “GLIDESLOPE, GLIDESLOPE!” - louder call


Mode 6 TAWS

Advisory call outs - rad alts and excessive bank angle

Inputs - rad alt, height bug, IRS (for bank angle)

Bank angle - 35 to 40* above 150ft

10* within 30ft to prevent wing tip and engine pod damage


Mode 7 - TAWS

Windshear alerting

Armed from rotation/missed aprch to 1500ft ra
aprch - 1500ft to 10ft

Inputs - airspeed, GS, rod/roc, AoA, changes to h/wind and t/wind

Windshear only gives warnings, no alerts


40 - 60secs before impact GPWS

“Caution terrain” and sold amber terrain


20-30 secs before impact

“Terrain, terrain. Pull up!” And pull up on PFD

Solid red on the ND



Prevents r/y incursions on r/y and taxiways

Provides an audible warning or approaching r/y and identifier


TAWS colour coding

Red = 2000ft or greater above the a/c elevation
Yellow = between 500 to 2000ft above a/c elevation
Green = 500 ft below the a/c elevation
Black = 2000 ft below the a/c elevation