Which type of system would be more reliable for keeping a plane traveling at constant speed - an automatically controlled feedback loop, or a manually controlled feedback loop? Why?

In order to keep the plane travelling at a constant speed, an automatically controlled feedback loop is more reliable.

Explanation:

The main reason behind this is that the plane needs to travel at a constant speed and that would only be maintained by setting constant feedback for the loop.

The feedback being constant will correspond to constant input which will, in turn, correspond to a constant output and hence constant speed.

In the case of using a manually controlled feedback loop, feedback will have to be provided manually at each iteration which is not practically viable as there is a scope for errors.