Garmin G2000 Pilots Guide - Page 425

SYSTEM OVERVIEW FLIGHT INSTRUMENTS EIS AUDIO & CNS FLIGHT MANAGEMENT 6.6 TAWS Hazard Avoidance Warning: Do not use TAWS information for primary terrain avoidance. TAWS is intended only to enhance situational awareness. NOTE: Government agencies provide data for the TAWS databases. Garmin accurately processes and crossvalidates the data but cannot guarantee the accuracy and completeness of the data. NOTE: Terrain information is not available when the aircraft is outside of the installed terrain database coverage area. The Terrain Awareness and Warning System (TAWS) is a software feature that provides the pilot with visual annunciations and voice alerts for potential conflicts between the current flight path and surrounding terrain and obstacles. The TAWS messages are advisory in nature only. TAWS satisfies TSO-C151b Class B requirements for certification. TAWS requires the following to operate properly: • A valid terrain and obstacle database • A valid 3-D GPS position solution TAWS uses terrain and obstacle information from government sources. Terrain information is based on terrain elevation information in a database that may contain inaccuracies. Individual obstructions may be shown if available in the database. Garmin verifies the data, per TSO-C151b. However, the displayed information should never be understood as being all-inclusive and data may be inaccurate. 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 then converted to the height above geodetic sea level (GSL), which is the height above mean sea level (MSL) calculated geometrically. The system uses GSL altitude for its alert calculations. GSL altitude accuracy is affected by satellite geometry, but is not subject to variations in pressure and temperature that normally affect pressure altitude sensors. GSL altitude does not require local altimeter settings to determine MSL altitude. It is a widely-used MSL altitude source. Therefore, GSL altitude provides a highly accurate and reliable MSL altitude source to calculate terrain and obstacle alerts. The TAWS terrain and obstacle databases are referenced to MSL. Using the GPS position and GSL altitude, TAWS provides a 2-D picture of the surrounding terrain and obstacles relative to the position and altitude of the aircraft. Furthermore, the system uses the GPS position and GSL altitude to calculate and "predict" the aircraft's flight path in relation to the surrounding terrain and obstacles. In this manner, TAWS can provide advanced alerts of predicted dangerous terrain and obstacle conditions. Baro-corrected altitude (or indicated altitude) is derived by adjusting the altimeter setting for local atmospheric conditions. The most accurate baro-corrected altitude can be achieved by frequently updating the altimeter setting to the nearest reporting station along the flight path. However, because actual atmospheric conditions seldom match the standard conditions defined by the International Standard Atmosphere (ISA) 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 GSL altitude. HAZARD AVOIDANCE AFCS ADDITIONAL FEATURES APPENDICES INDEX 190-01263-01 Rev. A Garmin G2000 Pilot's Guide for the Cessna T240 411