I wanted to ad something about the notion of "Flying Through" the AFCS.
I think it is vital tha the pilot understands exactly what flight path he has ordered from the AFCS whenever he presses an interface button. The GA mode of the EC225/175 is a classic example of this as it delivers something different depending on current IAS and how many engines are working.
If the pilot truly understands the shape and parameters of the impending flight path he should ensure, before deploying it, that the Earth will not get in the way of that flight path.
Flying Through a commanded flight path is a misleading statement a d can lead to serious attitude changes which in themselves can contribute to a cluster-f*ck along the flight path.
Why? Because there are essentially two fly through conditions possible. The first, and in my view the only acceptable one, is to assist the AFCS in achieved an IAS/VS/ALT datum with an appropriate control input. This may be done because the pilot believes the the AFCS is not reacting quick enough because of course it is limited in its immediate authority and rates in which it can modify attitude. However, if the pilot uses this option believing it is vital, he has either already chosen an unsafe flight path from the AFCS or he is simply not patient enough to let the AFCS do its clever work. For this scenario Training and Experience are key to overcoming this.
The second fly through involves the pilot trying to force the aircraft beyond IAS/VS/ALT datums he may have already commanded from the AFCS. Usually this occurs because he did not understand the shape and nature of the flight path he ordered from the AFCS or, as appears in this case, his monitoring skills are so poor he cannot believe that the AFCS is delivering the correct algorithm.
In this situation a modern digital AFCS will take the attitude to its authorised limits to fight the pilot inputs once controls are released.
HC - pressing the Trim Releases is a very dangerous practice especially during a night rig departure and in my view should only be done in an extreme situation. Where the required rate of attitude change to avoid impact demands it. Once the trim is pressed on the cyclic all notion of stability is lost.
Training pilots to use a modern AFCS takes patience, skill and knowledge from the Instructor. But more than this, it takes time! Most Type Rating Courses used by industry do not include any dedicated training on the AFCS. By that I mean real time board briefs and dedicated time just accessing AP functions with the sole remit to fully understanding each mode.
For the GA system of the EC225 this mode requires 2 hours classroom and 4 hours PF/PNF split, of dedicated SIM time. There is no way a pilot has a hope of understanding how it works without this. Thereafter, for the rest of the course, the GA needs to be integrated so the pilot understands how the flight path shape it delivers can be deployed to enhance the safety of his operations especially when close the the surface.