GPWS operating modes are automatically actuated when the aircraft is in one of the following flight configurations:
1. Excessive descent rate relative to cruise and approach phase altitude
2. Excessive rate of closure to terrain relative to altitude, flight phase, and airspeed
3. Altitude loss during take-off phase
4. Insufficient terrain clearance relative to flight phase and airspeed
5. Inadvertent deviation below glide slope beam during ILS approach phase
6. Call-outs warning of descent below pre-established altitude and selected decision height
7. Flying in dangerous wind shear conditions during take-off or final approach phase
Many aircraft will utilize flap position along with landing gear position information, capitalizing on the capabilities of the radio altimeter. In fact most airframe manufacturers will provide both operational as well as functional testing data for EGPWC. Frequently these assessments will require the use of specialized test equipment including air data simulation equipment. In most cases all airframe sensors that supply the TAWS will be verified as operational. Devices like TAWS provide the worldwide aviation maintenance community with significant challenges, such as the impact of an improperly rigged flap. In the case of TAWS equipped aircraft, this may signify that the aircraft is in a different mode of operation than in reality. In the event the system does not include the artificial intelligence needed to inform the flight crew of a disagreement in aircraft configuration, the crew may not be receiving the true picture as what would be considered hazardous terrain.
Airframe or TAWS manufacturers documentation should always be consulted to determine what airframe devices are tied to the TAWS and subsequent testing methods should always be employed to ensure continued airworthiness of the system.
Yes, it is still a given that gravity is going to triumph, but now it is almost a sure bet that we will only let it win on our terms.
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New regulations take effect in 2005.