Optimum altitude / Recommended altitude

[extricate]

Hi there,

Simply put, optimum altitude doesn't take into account of current atmospheric conditions but recommended altitude do. Do you always target recommended altitude as the cruise altitude (barring flight level availability) ?

[Deepinsider]

5 Optimum Altitude, Maximum Altitude, and Recommended Altitude
OPT—displays the optimum altitude based on airplane gross weight and speed
displayed on the speed line.
MAX—displays the maximum cruise altitude based on:
• current gross weight
• engine out operation
• selected speed option
• disregarding any altitude or speed constraints, and
• residual climb rate of 100 feet per minute.
RECMD—displays the most economical altitude to fly based on airplane gross
weight and cruise winds
Applicable to B788. Short answer to extricate is.. Yes

[Deepinsider]

to extricate, Hi.

I feel your question seeks a longer answer than my blunt yes.
Others may give us more info, but with the Boeing manuals
there seems to be a minimum need to know only culture ,
(possibly lawyer driven. MCAS etc?) I have only flown Boeing jets.

my suggestion is to track down the FMC OEM manual which
operators hold. It might address questions like how does a big
difference in actual wind vs. loaded winds affect the RECMD result.
It's important that uploaded wind/temp data is kept up to date if
on a very long haul. This should cover a wide range of altitudes too.

[extricate]

Exactly. The Boeing training manual speaks in general. That's why I wish to hear more views to this.

Thanks

[compressor stall]

If you have a perf app that can output solid data (or good manuals) pick a weight and temp, nil wind.

Get a spreadsheet, for each 2000' from FL280 to 400 determine the total FF and the CAS. Use an online calc to get the TAS which then equals GS. Do this for various cost indices.

Then plot the SGR across the X axis and alt on the Y. Gives a good feel for why optimum is optimum, what the effect of wind does (add / take a few kts from the CAS and see the effect). Quite powerful. You can see the delta kts to make a climb worthwhile.