Aterpster, re #127. Yes, Honeywell have promoted the use of an internal GPS card, but Airbus chose a different route.
The preferred Airbus option was for an external GPS/Nav sensor (MMR), which improved navigational accuracy and EGPWS performance (Operators Information Telex 5 Feb 04). Furthermore, at that time, they would not certificate “a solution based on a GPS card”.
Whilst this policy appears sensible in that it provides an accurate navigation (and terrain) map and thus should aid pilots to avoid situations where EGPWS may activate, the more complex (and expensive?) installation might result in fewer aircraft updates.
These aspects together with the apparent difficulty in isolating unsuitable navigation sensors might show as a difference between aircraft types.
Safety estimates circa 2000 comparing high vs low nav accuracy input to EGPWS, showed factor of two in favour of the high nav solution.
I have seen similar data for unmodified Airbus aircraft (2006) where the difference was also estimated to be two. I doubt that many aircraft would have been upgraded subsequently in the modern commercial climate. In addition, safety estimates considered the distribution of suitable ground based nav aids, the lack of which (at that time), further increased the risk of CFIT (associated with ‘map shift’) in less well equipped geographic regions.
Thus the lack of a high accuracy navigation input to EGPWS, the difficulty in isolating systems, and the very compelling features of map displays (our addiction to modern technology) significantly increases the risk of CFIT.
Several operators appear to have recognised these hazards and introduced procedures and training to mitigate the threats; noting that procedures and training are soft barriers.
Unfortunately humans forget (complacency), aircraft are sold on, but not necessarily with specific operational procedures and training, and humans remain vulnerable to the attraction of ‘salient’ displays, especially in stressful situations, and may overlook the most basic of safety behaviours when circling – staying visual.
EGPWS is one of the best (if not ‘the’ best) safety system, but it, like any other computer (and humans), depends on the accuracy of the inputs.
Whether these aspects have any relevance to this accident or not, it would be worth checking how current aircraft are equipped (first line of defence) and thus how they should be operated (last line of defence).