First, in the fields of writing objectives, validating the question bank and weeding out ambiguities, I was there, for Met, and I think that a generally sound job was done. As we go through the exams we, the FTOs, continually ask for revision of doubtful questions. Again, the CAA is generally helpful and flexible.
Second, in dealing with specific questions, IMHO, you have to be very careful. The matter of Vx and Vy is complicated. For a start, you can’t just use “Vy” without defining what Vy is. I suppose that a reasonably tight definition might be: “for a given aircraft and power plant installation, the EAS at which the power available exceeds the power required for level flight by the greatest margin at ISA msl conditions”.
Narrowing it down further, to jet powered aircraft, we find that Vy will be a figure determined by the shape of the power required and power available curves that are specific to one aircraft. Thrust, for example, usually varies with EAS, and the variation depends on the engine installation. What happens at altitudes above msl, and in conditions that are not ISA will depend on how the power available and required curves alter. This again will be specific to the aircraft.
Nevertheless, it is generally true for typical jet aircraft that Vy as defined reduces with increasing height. Note that Vy in CAS/RAS/IAS will rise in relation to Vy in EAS as TAS increases. The decrease in best rate of climb speeds can be marked. Figures in IAS for the atypical Hunter Mk 1 were:
msl. 430kt
10,000ft 400kt
20,000ft 365kt
30,000ft 329kt
40,000ft 260kt
The IAS given at the higher altitudes is defined by Mcdr.
The figures given in aircraft operating manuals, like those above, are not necessarily Vy as defined above. If wide variations of speed produce only small variations in time to height, it might be easier and simpler to use a single CAS in the climb. This, of course, is not the same thing as saying that Vy as defined is constant with increasing height. Air traffic control might also require a fixed CAS in the climb for traffic separation.
If you are short on power, you will soon arrive at a point where Vy has reduced to approximately Vimd and where you have no excess power available. Roughly then, Vy has reduced to Vx and you are at your absolute ceiling. This does not happen if you have unlimited power available. In those conditions, Vy will be constrained by Mcdr at first, with EAS reducing, and when the EAS for Mcdr reaches Vimp, again Vy and Vx coincide. Not that this has much practical significance, for terrain avoidance climbs are rare at FL400. Vy/Vx then remains at approximately Mcdr as you climb, with EAS reducing further, until EAS reduces to your minimum control speed. (Normally taken as 110%Vs1g). Vy/Vx remains at this EAS until Mach number rises to Mmo. Now you really have reached your absolute ceiling, coffin corner.
I hope I do not fall in to the same category as another instructor who said he did not make posts to show off his own skill and knowledge - and then demonstrated at least partial achievement of his aim! If you want the full picture, I recommend a book “Aircraft Performance Measurement” by Dr Eschelby at Cranfield.
Dick W