The Forward Looking Terrain Avoidance (FLTA) feature of TAWS compares the projected flight path as derived from GPS data with terrain features and obstacles from the terrain and obstacle databases. The system issues FLTA alerts when the projected flight path conflicts with terrain or obstacles.

The projected flight path is a calculated area ahead of, to the sides, and below the aircraft. The size of the projected flight path varies based on factors including ground speed (the path ahead is larger when the ground speed is higher), whether the aircraft is level, turning, or descending, and the proximity to the nearest usable runway along the current track. As the aircraft approaches the runway, the projected flight path becomes narrower until the system automatically disables FLTA alerts or the flight crew manually inhibits them.

There are two types of FLTA alerts, Reduced Required Terrain/Obstacle Clearance (RTC or ROC respectively) and Imminent Terrain/Obstacle Impact (ITI or IOI respectively).

The system issues Reduced Required Terrain Clearance (RTC) and Reduced Required Obstacle Clearance (ROC) alerts when the aircraft flight path is above terrain, yet is projected to come within the minimum clearance values in the following figure. When an RTC alert is issued, the system displays a potential impact area on the ‘Map’ and the PFD.

Imminent Terrain Impact (ITI) and Imminent Obstacle Impact (IOI) alerts occur when the aircraft is below the elevation of a terrain or obstacle in the aircraft’s projected path. ITI and IOI alerts are accompanied by a potential impact area on the ‘Map’ and the PFD. The alert occurs when the projected vertical flight path is calculated to come within minimum clearance altitudes in the following figure.

The system automatically inhibits FLTA alerts when the aircraft is less than 200 feet above the destination runway elevation while within 0.5 NM of the approach runway or the aircraft is between runway ends.