GPWS is effective over water and level terrain - it is a lookdown system only. The GPWS algorithm uses the RADALT as the primary sensor, along with INS and ADC information for protection computations, which are then fed into the GPWS computer or platform computer. Warnings from the computer are sent to the Pilots headset and Display. GPWS provides no protection in rising terrain, lacking a forward looking capability.

Terrain Awareness Warning System (TAWS) utilizes GPWS, digital terrain data, and GPS to provide the forward looking capability. This expands protection over all types of terrain, including rising terrain.

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