Terrain - Garmin GNC 420A Installation Manual

4.11

TERRAIN

Terrain Awareness and Warning System (TAWS) is meant to provide the flight crews with both aural and
visual alerts to aid in preventing an inadvertent Controlled Flight Into Terrain (CFIT) event. While the 400
Series unit cannot be fully TSO-C151b Class B TAWS capable due to hardware constraints, a TERRAIN
version is available. The 400 Series TERRAIN version is intended to provide a non-TSO-C151b-certified
TAWS-like capability.
The table below highlights the functional differences between TAWS, TERRAIN, and None.
TSO-C151b Class B Certified
TAWS/TERRAIN Display
( Shows terrain elevations relative to the aircraft )
Visual Alerting
( Includes popup alerting )
Aural Alerting
External Visual Alerting Capability
Reduced Terrain Clearance (RTC) Avoidance
( Forward Looking Terrain Avoidance (FLTA) sub-
function )
Imminent Terrain Impact Avoidance
( Forward Looking Terrain Avoidance (FLTA) sub-
function )
Premature Descent Alert (PDA)
Excessive Rates of Descent Alert
( Ground Proximity Warning System (GPWS) Alerting
sub-function )
Negative Climb Rate/Altitude Loss After Takeoff
( Ground Proximity Warning System (GPWS) Alerting
sub-function )
"Five Hundred" Voice Callout
( Ground Proximity Warning System (GPWS) Alerting
sub-function )
Inhibit Capability
( Inhibits FLTA and PDA visual and aural alerting )
TAWS Test System Capability
Worldwide Terrain Database
Airport Layer Database
Obstacle Database
400 Series TERRAIN functionality is a subset of TAWS functionality and has been certified as a non-TSO
function. As such, a subset of TSO-C151b specification is used as the requirement basis.
400 Series TERRAIN functionality is not designed nor approved for use in helicopters.
400 SERIES INSTALLATION MANUAL
190-00140-02
Function TAWS TERRAIN
Yes No
Yes Yes
Yes Yes
Yes No
Yes No
Yes Yes
Yes Yes
Yes Yes
Yes No
Yes No
Yes No
Yes Yes
Yes No
Yes Yes
Yes Yes
Yes Yes
None
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
No
Page 4-21
Rev Q