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G.Franco Corrias

Optimum Altitude cruising

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Optimum-altitude-1.jpgBy this Boeing chart it's possible to plan and check a B742 flight.Let's assume this example:T.O. weight=345.000 kgs /760.000lbsOAT=STD+15From the Flight plan considering our cruising HDG we have to fly at an ODD level.So we have to choose among:FL 270FL 290FL 330FL 370FL 410From 345.000/760.000 weight we follow the oblique lines due to the fuel consumption during TO and Climb and we have to choose as our maximum cruising level FL 330 because FL 370 is over the BUFFET ON SET 1.3g line and over the STD+15 line.BUFFET ON SET line is the for the Stall tolerance and STD+15 is for the engines perfomances necessary for our cruise at mach 0.84.Fortunally we start the cruise over the -1%SR(specific range)/5Headwind line and we proceed towards the OPTIMUM ALTITUDE line.The best should be to have the possibility to fly always over the OPTIMUM ALTITUDE line but for obvious reasons it's not possible to fly a continuous climbing cruise.The best way to remain as near as possible at the OPTIMUM ALTITUDE is to fly from the upper -1&SR/5Headwind to the lower -1%SR/Headwind lines.After having crossed the OPTIMUM ALTITUDE we proceed and reach the lower -1%SR/Headwind.It's time to ask the ATC for an higher level.The only possible ODD level is FL370 because FL410 is over all security lines.So we climb to FL370 and we start our new cruise a little bit over the -1%SR/5Headwind line.We'll cross again the OPTIMUM ALTITUDE and when the lower -1%SR/5Headwind line is reachedwe ask to climb to FL410.FL 410 will be our final level until the descent to destination airport.Hoping this has been interesting for RFP communityGianfranco

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