Bealzebub
I do indeed take your point and understand it to the fullest. I stand corrected until i read otherwise
I don't fly so my only experience with fuel consumption of an aircraft flying at an unpressurised altitude is the example I gave before..
Bear with me.....
Normal fuel load for the sector with pax and cargo 13,000 kgs
Ferry flight no pax or cargo flying 10,000 feet same sector fuel required was approx 20,000 kgs
I think blind Freddy would draw the same conclusion in that best fuel consumption is very much dependant of the most efficient operating altitude and it would appear 10,000 feet is not the most efficient altitude.
If you have an engine failure on the a "light twin" the operating engine goes to a thrust setting very close to max continuous...burning lots of fuel. You burn more fuel at see level for a given epr than altitude due to fuel metering at a ratio approx 8:1 weight air to fuel( i hope we agree).
E.G. doing a trim run on a 767 for an hour at sea level (part power setting, this is below max continuous) will easily burn 10,000 kgs of fuel in an hour . In 179 minutes you will burn at sea level approx 30,000 ks of fuel. If a 767 fully fuelled to 68,000 kgs and has failures, engine out and pressurisation loss in the later half of the flight.
There may be a problem reaching your diversion point.....
I admit I assumed.
You have wet my appetite. Now I will have to find the absolute answer to this...
Bolty