Quote:
Originally Posted by NJA_Capt  I don't have a book at home, but I ran it through the FMS software. For a 2 hour flight, the FMS calculates an "optimal" cruise at FL280. Running a "What If" calculation for FL370, the leg time decreases by 1 min and 1000# fuel. For a 3 hour leg it was also 1 min quicker / 2000# less fuel. |
I'm assuming wind was not involved in this calculation. The above doesn't make sense to me.
I ran through some performance charts for Mach .80 cruise for the 767. From FL260 to FL430, the TAS decreased linearly above FL 280. So did the fuel flow.
I wonder why the FMS calculated FL280 as optimum? It is showing higher altitudes going faster and burning less gas.
The only other explanation would be a buffet boundary/stall protection issue...but there is no way at FL280 that would be an issue at even the heaviest of weights...and least I would assume.
That makes me wonder if some winds were programmed in the scenario?