Originally Posted by
Derfred
I didn't make that up, it is SOP clearly published in the FCOM. If you can't find it, I'll give you the references.
... It's not complicated, and it's Boeing SOP.
If your operator publishes a different SOP then follow that. In that case the argument is with your operator not with you. But if your operator thinks they are following Boeing SOP, they may be mis-interpreting this FCTM amendment, and perhaps they should pick up the phone to Boeing and sort it out. Boeing will probably say "set final cruise alt", but get them to explain that. Final cruise alt is generally defined as TOC alt, not TOD alt (hence all this disagreement).
I think there are different version of FCOM as each one is Operator adjusted, including yours, sorry to say. So your statements above refer to
your operator interpretation of Boeing's SOP, the master versions can be referenced by your Boeing representative...
Let us just finish to say that although you are correct in the sense that you have a possibility of multiple CRZ levels, it is this very reason that Boeing refers to adjustments as one such climb may trigger the higher differential found (only) on NG when passing FL370. This very reason has caused issues, including high (yes up to 1000 fpm) cabin descent rates while the mode controller is adjusting to the new selected differential that is required. This very change in pressure during cruise is what is to be avoided, as per Boeing, and can be done by selecting final cruise level...
If your operator defines initial cruise as that to be set in Flight Altitude window, that is your SOP, other operators, especially those having experienced events as described, and those operating ETOPS with very long sectors (like those including me who flew a BBJ ETOPS 180) the final level set is that ultimately achieved for two reasons:
- passenger comfort during climbs, ths avoiding a high rate descend in cabin during climb at some point in flight;
- avoiding pressurisation changes during flight on the structure