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I thought fuel pumps were reserved for fuel injected planes in startups and during critical flight phases for all planes?

However. There are some X-Plane flight tutorials that tells us to use fuel pump in startup of C172 aircraft as if we are flying a fuel injected plane. I don't think its necessary for an gravity fed engine but why would someone use fuel pump in a high wing carburetor plane start up? Isn't it a waste of battery?

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  • $\begingroup$ I am in a hurry so I can't check which video was that tutorial sadly. $\endgroup$ – Delta Oscar Uniform May 9 at 16:24
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    $\begingroup$ When you are playing a computer game, follow the game tutorials. If you are flying a real aircraft, follow the POH. $\endgroup$ – Michael Hall May 9 at 22:12
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Many 172s are fuel injected.

I've flown both carbureted and injected 172s.

On a carbureted model, you prime by pumping the primer between 2 and 5 times.

On a fuel injected model, you prime by running the fuel pump for about 3 to 5 seconds with the mixture open.

As for why you do that, the short answer is because the POH says so.
The more precise answer is that gravity feed alone is not enough to push fuel through the fuel injectors (which are very tiny little holes in the cylinders)

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  • $\begingroup$ Correct, and the stock C172 in X-Plane is an SP so definitely a fuel injected version. $\endgroup$ – jwenting May 10 at 3:34
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Typically, fuel pump is turned on to make sure it works, and then off. Fuel pump is only used in flight if gravity-fed fuel pressure from the wing tanks drops due to flying at extreme angles of attack.

Not a waste of battery, as you would be using electricity from the engine driver alternator.

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  • $\begingroup$ Huh. Weird to see its not a part of the checklist. $\endgroup$ – Delta Oscar Uniform May 9 at 16:28
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    $\begingroup$ It's on the checklist for my C177B, which uses the same arrangement. See Page 4-12 of the C172SP POH aeroatlanta.com/docs/aero-atlanta-c172sp-poh.pdf 6. Auxiliary Fuel Pump Switch -- ON. 7. Mixture -- SET to FULL RICH (full forward) until stable fuel flow is indicated (usually 3 to 5 seconds), then set to IDLE CUTOFF (full aft) position. 8. Auxiliary Fuel Pump Switch -- OFF. $\endgroup$ – CrossRoads May 9 at 16:33

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