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A
The temperature decreases and thereby compensates for the decreasing air density which is caused by the decreasing pressure. Therefore the fuel flow remains the same.
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B
The temperature decreases and thereby over-compensates for the decreasing air density which is caused by the decreasing pressure. This results in a decreasing fuel flow.
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C
With increasing altitude air density decreases and the power output of the engine decreases. This has to be compensated for by an increased fuel flow.
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D
With increasing altitude air density decreases, therefore less fuel is required for combustion, so the fuel flow decreases.
As altitude increases, the air density decreases, which means there is less oxygen available for combustion. Therefore, less fuel is required to maintain a constant power output. So, the fuel flow will decrease, not increase. Increasing the fuel flow in an effort to compensate for the decrease in air density would result in an over-rich mixture and potentially cause engine damage.
What exactly do they mean by "maintaining the same power setting?". We believe it is referring to the amount of power the pilot is requesting from the engine, not the actual power output of the engine. In order to maintain the same power setting, the pilot will likely have to lean the mixture (decrease the fuel flow) to compensate for the decrease in air density at higher altitude. So, even though the pilot is requesting the same amount of power, the engine will produce less power due to the decrease in air density, and the fuel flow will decrease to match the decrease in oxygen available.
Note: We are deciding that "power setting" means constant RPM/MAP for this question. Please let us know if you come across this question in your official exam.
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This question has appeared on the real examination, you can find the related countries below.
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Austro Control2
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Hong Kong1
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Pakistan1
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United Kingdom1
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