In article . com,
Bret Ludwig wrote:
There should be a interlink which brings engine power to flight idle
any time cabin pressure is lost above FL180. The aircraft wil descend
under autopilot. There is statistically very little terrain above
18,000 feet and what there is is unpopulated.

With all the fancy nav equipment you could do better. Just tell the
computer to descend to, say, 10000 "unless you're over the Andes,
Himalayas, etc."