Thought so. Seems like it chooses a cruise Mach for the FMS ECON speed based on cost index (let's say for example, arbitrarily, .612 Mach at 17,000 feet) and a climb IAS that typically crosses over to the cruise Mach a couple of thousand feet below the cruise flight level (let's say ECON climb would be something like 294KIAS / .612 on the PERF page).
So, climbing through 10,000 it accelerates from 250 to 294 knots, maintains 294 knots until around 15,000 feet where Mach crossover to the selected ECON Mach number occurs. 294 PITCH changes to .612 PITCH on the FMA, and the airplane zooms up slightly to maintain the Mach number, slowing to around let's say 280-285 knots in the couple of thousand feet prior to levelling at 17,000 feet where it enters cruise flight with the FMA showing .612 THRUST.
Makes sense why it would be programmed that way up at high altitude where Vmo exceeds Mmo (normal Mach crossover technique), but it just doesn't make sense to my dense mind WHY they would have chosen to program it that way regardless of cruise level. Sometimes it seems like it can give an uncomfortable ride in those last couple of thousand feet, especially if there happens to be an increasing headwind in that altitude band, whereupon the plane starts skyrocketing up to chase the ever-decreasing airspeed target and then immediately pushes over to level off. Usually just level it in VS if it starts doing that.
Sounds like lazy programming to me, but hey, I'm not that smart!
