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.
