MD-80 Rocks! Stuff Open Climb!!
On the MD-80 we sometimes flew high at the edge of the aircraft’s performance envelope (in those days the performance tables and aircraft weight were not so exact) and encountered buffeting in turns with more than 10° bank.
If you entered the top layer of a thunderstorm in such conditions, you could lose lift rapidly and disappear in the cloud.
In 2006 I flew a heavy A321-200 above its maximum recommended flightlevel to get over a thunderstorm.
With open climb mode I anticipated a slow climb.
Checking the primary flight display it showed an unexpected ROC of 3,500ft/min with rapidly decreasing airspeed.
What happened?
The computer extrapolated that beyond normal range the aircraft would not be able to fly high and fast simultaneously, and reduced speed to M.73 by itself.
To get there from M.79 it pitched up to a ROC irrationally high in thin air.
It would have meant stalling and falling into an active storm.
The A321 software may be updated to avoid this condition but it shows the vigilance needed at the edge of its performance envelope.
A computer-controlled aircraft is still only an aerodynamic machine.