My take on the Perf exam. Don't take my view as gospel as I am not entirely confident about it:
Maintaining constant CAS as you climb, what's going to happen with Angle of Attack and Pitch angle?
That is a tricky one. The aspect is that you must ignore compressibility to answer it. I think the question specified this...not sure. Without compressibility then EAS and CAS are equal so AoA Decreases and Pitch Decreases with the reduction in thrust. With compressibility, the right answer (IMHO) wasn't present (both increase).
The typical question on why we use cruise climb technique.
I don't remember that one! I vaguely remeber a question on why the cruise climb cannot be used...basically why use step climbs. Maybe I have lost the plot and confusing the exam with feedback.
Why would you NOT fly at optimum altitude?
I think the question was "Why would you fly 4000' lower than optimum?" Easy as there was only one sensible answer and it was worded as a signification reduction in headwind or a large increase in tailwind.
I think they also asked about Density Altitude, can't say for sure cause I took both exams on same day.
They did and it was just asking for a definition. Pretty straight forward.
When would Vmcg be lowest? (I think it was more like> WHY is Vmcg something and the answer was, decreased thrust)
(this question is definitely in feedback)
Vmcg is lowest when thrust is least and so a lessened asymmetric thrust effect so it is easier to control with an engine out so the right answer always appears to be when hot'n'high.
What happens with speed Vx and Vy as altitude increases?
Another horrible one as we have to guess if they intend to account for compressibility. My guess is that they do and so both increase to maintain a constant EAS. However, if you look at the Power/TAS chart the TAS also increases BUT my notes say that Vx remains constant and Vy decreases!! Did the question specify TAS? Probably one I got wrong.
What speed would you fly in case of driftdown?
This was an horrendous question as I don't recall it actually having the word "driftdown" in the question. I seem to remember the question was what speed for a twin jet, one engine out, in the cruise in a mountainous area, maintaining clearance? The options were CD/CL(MAX), LRC, CD/CL(MIN) and Max lift to drag ratio!! Two right answers for a driftdown. As it didn't actually ever mention a driftdown but S&L (Cruise) I was completely confused. Even CAP698 didn't help. Everybody appealed this.