Mr Desk Driver, I am a pilot and an engineer..... and yes, you do stand to be corrected.
Firstly, the GPWS does not know that if it is flying over steeply rising ground, when in the future that rising ground will cease. Thus it can be fooled and regularly is around certain areas approaching some airports. The mountains south of Dublin airport are a good example.
Also many aircraft including buses are fitted with Enhanced GPWS which also uses topographical data on disk to warn of terrain ahead. If as in the case of the new Athens airport the data was incorrect, then aircraft will again receive false warnings until the problem is corrected.
You can also receive false warnings from aircraft passing legally a thousand feet below in the hold or passing under the aircraft on an airway.
I would not want to comment about any particular instant such as GMONX into GIB (unlike The Sunday Times) until I knew all the facts. Because when you make an assumption .......... it ain't necessarily so !! (sounds like a good line for a song
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