Best TAS
 

OK - I know I could work this out if I got into the books - but can anyone give me a (the) formula for height to fly, at a given Mach no, for max TAS?
Sorry to be so sad, M

You need to find the point for your aircraft where the Vmo meets the Mmo - this is the point of max TAS for your aircraft.

For the 146 (Vmo 295kts, Mmo 0.7) it is about F240/F250.

Thanks; in fact I plotted M0.82/330 kts IAS (using the good old Dalton Confuser) for the 757 and got a best TAS ht of FL 275 - a lot lower than I imagined. I was looking for a formula that I could just plug the numbers in - but spinning the wheel is as good a way of passing standby as any, I supppose!!