Originally posted by Keith Williams
It may be the case that flat rating compensates fully for the temperature-induced loss of static thrust before brake release, but does not compensate for the thrust reduction caused by increasing TAS during climb out. If this is the case, then the thrust available during climb out will be less than the rated value and will decrease with increasing OAT even within the flat rating temperature range.
I wondered about that - net thrust is gross thrust minus momentum drag and the flat rating relates to static gross thrust. But the momentum drag is mass flow*TAS, so although the effect you describe is I think there, the magnitude will also depend on how the engine mass flow varies with temperature in the flat rating zone. From what I have read the CF34 is flat rated to constant N1/root theta, which (I think!) would mean actual mass flow reducing with increasing temperature and the gross thrust flat rating being maintained by increasing TET.
If I'm right then the mass flow would go down as root theta and the speed go up as root theta so the thrust lapse rate would not be affected by ambient temperature, if the mass flow stays constant then your explanation could be the answer. But I am not an engine man and I stand to be corrected !