Suggest you do what FCOM recommends - they built it - they certified it - they know what they are talking about as a result of a whole heap of information not available in FCOM. FCOM is an abbreviated technical document for users(pilots) and is the summation of a large mass of technical investigation derived from flight test data.

Select speed - either recommended Mach or IAS dependent on altitude - as per FCOM
If the turbulence is severe - as per FCOM

Investigation reports are littered with home grown variations which do not have the manufacturers endorsement or recommendation - the lawyers love it !

1.Policy
2.Procedure
3.Technique
4.Advice

Be very wary of the last two when information comes from someone who thinks he/she knows better than the manufacturer !!

ps
ATHR response (lag) can vary slightly depending on the engine fit

Happy flying :O:O

TyroPicard... I am glad my college teacher did not see what I wrote... Thanks for the correction.

As far as I know, all you need for soft mode is ALT CRZ.

Soft mode is not good in mountainwaves, in my experience

I actually tried it today. Couldn't find anything about it in the FCOM but on the V2500 engines, selecting SPEED in stead of MACH actually gives a faster reaction in A/THR operation at high altitudes.

ALT CRZ still allows for the +/- 50 ft, but A/THR reaction to speed changes are faster. Interesting to see but nothing to backup this "feature" in the FCOM

Anyone any reference on this??