I recently watched an Air Crash Investigation episode where Qantas flight 32 lost an engine shortly after takeoff. It was revealed that a stud pipe in a Rolls-Royce engine was made incorrectly, causing the pipe to snap and burst through the engine and the aircraft's wing, severing major hydraulic systems, and causing the ECAM to display pages and pages of errors.
On the final approach, the captain announced he wished to perform a ‘control check’. He said (and this is approximate):
When the aircraft is damaged, you have to certify it is safe to land before you try to land.
I assume this is so that the captain can make the necessary preparations if he feels his aircraft is not safe to land. On flight 32 this was done by moving the stick left and right to simulate lining up with the runway.
Perhaps a better question is back to the post's title.
What are the purposes of in-flight Control Checks?
In my example of Qantas Flight 32, the stick was moved left and right on final approach to simulate lining up with the runway. This was only small left and right control deflections. The flight deck had only minutes until landing. What was the captain expecting to see, or not to see? Can the captain after that brief manoeuvre be aware of his aircraft enough to make a decision?
Does this mean then that a Control Check only comes, or should only be done, if you are worried that the aircraft cannot land? Can it be done at any other time? In other words: is an in-flight control check only done for landing?
Wikipedia Flight 32: https://en.m.wikipedia.org/wiki/Qantas_Flight_32