It was more a case of sluggish auto thrust response an increasing tailwind over a period of about 40 seconds in ALT CRZ.
The aircraft had been stable in the ALT CRZ with the thrust set at 87.5%. The wind shifted and the IAS washed off by about 9kts or so over the period of about 30-40 seconds but the thrust remained at the previous setting. Eventually the auto thrust decided that the deviation warranted the addition of power, the engines wound up to full power and the aircraft smartly returned to the managed target speed.
I have found that there is a bigger delta between thrust required to sustain cruise speed at/near green dot and rated thrust at Rec Max on NEOs vs CEOs. Typically 8-9% on a NEO vs maybe 3-4% if at Rec Max on a CEO.
In the scenario described above, if the aircraft has been a CEO, I am certain I would have had to initiate a descent to get back on the right side of the drag curve. I certainly consider the 1000’ margin prudent on the CEO and I practically never push above it unless operationally necessary, being well above the tropopause and in very smooth air, not crossing high terrain.
Last edited by speedrestriction; 24th Oct 2021 at 22:40.