Originally Posted by
Paulm1949
Thanks. Would you climb in Mach or IAS at higher altitudes with the a/t not working?
Without being blunt i'm not sure why this would be a question? The fact you don't have a working A/T doesn't have any bearing on that - at high altitudes a jet airliner is operated at mach no, at lower altitudes by IAS.
You'd set climb N1 manually and climb in IAS until you reach your climb mach no, just as you would any other day with a working A/T.
Remember that in LVL CHG mode and VNAV SPD the thing controlling your speed is not your engines but your elevator (horizontal stab in fact). This is why I would suggest it is safer than V/S, the consquence of not having enough / having too much thrust in LVL CHG is that you simply don't climb / descend with as much rate. The consequence of not having enough / too much thrust in V/S is that you may stall or overspeed.