How Advanced GPWS functions
 

In the other forum a few posted stated that when a plane is in landing configuration the GPWS does not function. Is this accurate? I would think that would be the most important time for GPWS as you are approaching the ground. Especially with Advanced GPWS that most airlines have now where all the terrain and objects are programmed in. What happens if the pilots screw up and try to land a mile before the runway and instead are heading right into a mountain. You're telling me there would be no GPWS warning?!

Advanced GPWS has like 8 modes. The one with the landing gear down, is less sensitive to being close to the ground though. Advanced GPWS uses GPS and a map of terrain + towers to determine what a safe altitude should be according to the configuration of the aircraft..

As one of the people who posted "GPWS does not function" in landing configuration, I realize I should have been far more specific. I did not want to become too complex. The various modes in the current sate-of-the-art warn of diversion from expected ("normal") ground proximity for the phase and location of the flight. It now integrates not only radar altimeter- measuring distance from ground, but also the actual terrain including obstructions. Those also integrate with the flight plan, approach procedure and approach path.

The confusing part is that there are other related warnings that have existed for years, but are only now being integrated in what has become known as GPWS. These are "precision approaches, the most common of which is the Instrument Landing System (ILS) which provides both visual and audible warnings of proper approach path, and further, in the most advanced versions allow landing with no visibility at all. http://en.wikipedia.org/wiki/Instrument_landing_system These have nothing inherently to do with GPWS, but provide equivalent protection in landing approach.

One can get hugely complex about all this. In sum GPWS was conceived primarily to protect aircraft when not in a precision approach. Now these topics are beginning to merge from a practical perspective but not yet from a legal and regulatory one.

I hope I have not made the issue worse with this commentary.