There are five fixed thrust modes. TOGA, FLEX, MCT, CLB & IDLE. When thrust is in one of these the speed is maintained by varying the pitch. In TOGA/FLEX it's in SRS which is also pitch mode. If you want precise ROC/ROD then the thrust will be in speed mode and it will vary to maintain speed.
Last edited by vilas; 30th Mar 2021 at 12:47.