Hi,

all three axes of movement in flight are sensed and the appropriate actuator is selected
only roll control can be achieved
a torque limiter controls the aircraft in pitch

First of all, we are dealing with systems called closed loop feedback error cancelling systems that occur all over the aeroplane in various controls. Right away we have to note that "control" as a noun refers to all sorts of big and little systems and not just to aircraft flying controls like the elevator.

"Control" as a verb has a general meaning but in this section it is given a specific meaning - to control an aircraft in flight.

The principal behind a closed loop etc. etc system is that you can measure what your control system (in the general meaning) is giving you as an output, feed this back to the input side, determine the "error" or difference between what you want (input) and what you are getting (output) and then order the system to reduce(cancel) the error so you finish up getting an output that is exactly what your input asked for.

In an aircraft flying control system there are hundreds of loops of this kind all working inside one another. The small inner loops deal with dull things like giving you the elevator angle you wanted. Outside these dull loops more and more complicated loops encircle them, working up through holding a specific aircraft attitude to the final big one, delivering the aircraft performance (rate of climb, speed etc).

Now this is an immensely complicated subject, and to try and keep it simple an attempt is made to differentiate between the dull inner loops and the more exciting outer loops by using the concepts of "stability" for the dull loops that do not really fly the aircraft and "control" for the outer loops that are involved in aircraft control. Then, just to add complications, the concept of "performance" comes in. The loops concerned with aircraft performance are the real outer loops, so "performance" as a loop description overlaps with "control" Which is how the answers you saw have been derived. It is messy, but that is what the QB has, so stick with it for the exam.

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