Peter writes:

True, but they had one and it gave them no warning until way too late.
It was just a radalt in that case. Went off at about 200ft - no good
for ~ 250kt into rising snow covered ground.

Exactly. As I recall, the real problem was that the routing had been changed
and the crew was not made aware of this. They thought they were flying the
prior route which always took them well clear of the mountain, but in fact
they were moving directly towards it. Optical illusions and visibility issues
made it difficult to recognize the mountain, and by the time the warning
sounded, they were too fast and too close. See:

http://en.wikipedia.org/wiki/Mount_Erebus_disaster