Hi Crab, with the V/S installed in 3 axis mode it is active on the Cyclic "Pitch" channel. I was fairly certain they had set an ALT.A at MDA.
The incipient reduction in IAS during the descent would have been small compared to the effect when the ALT engaged automatically at the MDA.
During our L2 Type Training at the same Operator, the Training Staff went to great lengths to demonstrate this effect to us to dissuade us from engaging in this potentially dangerous practice,. We called it "The L2 tail slide" as that is what it felt like at the extreme.
As an aside, the PM took a hit for not monitoring the IAS. However, at the point of level off at MDA, the PF should be primarily monitoring the Instruments and the PM looking out for the Required Visual References. It raises an interesting argument and further supports the practice of CDFA where there is no level off and therefore no prolonged attempt to gain visual references and thus less opportunity to lose the IAS.
This single accident raised a lot of issues. All inter related and all significant.