Light aircraft elevator/aileron/direction not working
If a major flight control surface fails in flight, you'll be lucky if the ballistic parachute can save you.  An aileron, for instance, that goes &quot;hard over&quot;, will put even the most docile training aircraft into a tight spiral or a roll that will quickly become a spin (because the airplane doesn't have enough speed for a complete roll and will stall).  A stuck elevator could result in anything from a stall to a steep dive.
In this situation, immediate deployment of a ballistic parachute might prevent fatalities; waiting will not.  Delay will allow airspeed to build, G forces on the pilot to increase (presuming a spiral or spin), and potentially the wings come off due to flutter or G forces after passing Vne -- not to mention likely exceeding the parachute's maximum deployment safety margin.
Fortunately, this kind of failure is exceedingly rare, absent the kind of damage that comes from air combat, ground impact, or extreme weather phenomena.