Wingswinger
A CDA is not a descent in idle, it is a continuous descent (min I believe is 500fpm) with an allowable level segment (without checking think it is 2 mile i'm sure someone will correct me).
Therefore once you are established on the glide most people will only be at approach idle to get the speed back after 4 miles, where you have invariably been maintaining 160kts.
Ergo I think CDA's have little bearing on this incident.