SR I don't quite agree.
OPT alt, is the altitude that minimizes trip cost when ECON speed is selected.In other words, OPT displays the most economical altitude to fly, based on gross weight.When LRC or SEL SPD is selected, OPT alt displays the altitude that minimizes trip fuel.
RECMD alt is the recommended cruise flight level to fly at for the next 500 NM. This calculation is based on the following:
- Specified route
- Selected cruise speed schedule
- Estimated aircraft drag and fuel flow information
- Wind and temp forcast
The recommended flght level can be any flight level in the present step altitude schedule up to the maximum altitude ( MAX ALT) and down to 9000 ft below the current FMS cruise alt.
The big visual difference on the FMS is that OPT alt increases in 100 ft increments for obvious reasons.
RECMD alt is always a flight level based on selected step climb of either 4000 ft (ICAO) or 2000 ft (RVSM)
Laters