Changeover altitude????
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For a typical climb schedule
(a) in the lower levels the aircraft maintains a constant IAS.
(b) as the altitude/flight level increases, the mach number progressively increases as TAS increases and speed of sound decreases. At some specific altitude, which is easily calculated, the desired mach number for higher altitude climb is achieved. The remainder of the climb is then done at constant mach number.
The level at which the change from constant IAS to constant mach number climb occurs usually is called the changeover altitude or level. Not specific to a particular aircraft - only the selected IAS and mach number.
(a) in the lower levels the aircraft maintains a constant IAS.
(b) as the altitude/flight level increases, the mach number progressively increases as TAS increases and speed of sound decreases. At some specific altitude, which is easily calculated, the desired mach number for higher altitude climb is achieved. The remainder of the climb is then done at constant mach number.
The level at which the change from constant IAS to constant mach number climb occurs usually is called the changeover altitude or level. Not specific to a particular aircraft - only the selected IAS and mach number.
PPRuNeaholic
Join Date: Jun 2000
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Yes, I think that context is important here. F'rinstance, my Kingair doesn't get to those sorts of speeds but we have a changeover altitude where fuel flow becomes either more important, or less important, than ITT. In the tropics, where I operate, if I'm flying at or below 18,000 feet (our transition altitude is 20,000 feet, in case you're wondering), ITT isn't critical in normal two-engine cruise, but fuel flow for optimum ITT is above our "magic" value of 300 pounds per hour.
Thus, we operate at 300 pounds per hour, indicated fuel flow, and accept the lower ITT.
Above 18,000 feet in normal two-engine cruise, ITT becomes important, so we fly ITT - plus or minus a bit to match N1 of course - and happily accept a lower indicated fuel flow value. Thus, 18,000 feet is our own version of "changeover altitude".
Having said all of that, I guess the intent of the original question has most likely been met by John_T amd BIK.
Thus, we operate at 300 pounds per hour, indicated fuel flow, and accept the lower ITT.
Above 18,000 feet in normal two-engine cruise, ITT becomes important, so we fly ITT - plus or minus a bit to match N1 of course - and happily accept a lower indicated fuel flow value. Thus, 18,000 feet is our own version of "changeover altitude".
Having said all of that, I guess the intent of the original question has most likely been met by John_T amd BIK.
