the CESSNA CITATION 3 has an Automatic Descent Mode function.
If AP on, altitude >35000`, cabin altitude > ~12000`, then the ADM function kicks in.
That means A/C turns 90 deg. left, and descents at MMO/VMO to 15000`. Only thing you have to do, is throttles to idle, and extend the speedbrakes.
Fantastic system, should be on all jets !