TERRAIN AWARENESS WARNING SYSTEM (TAWS) (Cont)
MODE 4 — Unsafe Terrain Clearance
Mode 4 provides alerts and warnings for sufficient terrain clearance based on the airplanes phase of flight and speed. Mode
4 requires radio altitude, computed airspeed, gear position and flap position inputs. The alert and warning envelopes are
based on minimum allowable terrain clearance as a function of computed airspeed.
Mode 4 is divided into 3 sub-modes: Mode 4A, Mode 4B, and Mode 4C.
MODE 4A
Mode 4A is active when the airplane is in cruise or approach phase of flight and the landing gear is not in the landing po-
sition. The alert envelope for Mode 4A begins at 30 feet AGL and extends vertically to an altitude of 500 feet AGL. During
penetration of the alert area above 190 knots, the upper boundary increases with airspeed to a maximum of 1000 feet radio
altitude at 250 knots or more. This annunciates an amber
GND PROX
display and generates a continuous aural “TOO
LOW TERRAIN” warning. Penetration of the alert area 190 kt, annunciates an amber
GND PROX
alert on the PFD and
generates an aural “TOO LOW GEAR” warning. The aural and visual remains until the airplane exits the envelope.
C
F
O
17
01002_016
MODE 4A UNSAFE TERRAIN
CLEARANCE
RUNWAY
"TOO LOW
TERRAIN"
AIRCRAFT SLOWED TO
LESS THAN 190 KTS
"TOO LOW TERRAIN"
"TOO LOW GEAR"
100
0
200
300
400
500
600
700
800
900
1000
1100
1200
1300
1400
1500
100
200
300
400
0
M
IN TERRAI
N
CLEAR
ANC
E (
F
EET
)
COMPUTED AIRSPEED (KTS)
UNSAFE TERRAIN CLEARANCE
GEAR UP, FLAPS UP
TOO LOW GEAR
WARNING AREA
TOO LOW TERRAIN
WARNING AREA
Challenger Global 300 - Navigation
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