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Old 7th Feb 2009, 05:55
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Zoyberg
 
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737 NG optimum flight level reduction with reducing mach no.
737 NG optimum flight level reduction with reducing mach no.
Can someone explain how my 737 optimum altitude is calculated.

Yesterday I completed an automatic FMC max rate climb to meet an ATC restriction ... the speed came back to 230 knots/0.68 mach and approaching FL350 ....ISA -10...at 69,000 tonnes the FMC optimum calculation was around 3,000' lower ( I would typically expect FL380 @ 0.78 mach in these conditions).

I understand part of the calculation is based on the fuel cost index (cost index zero giving the highest optimum)?

Thanks in advance.
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