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enter image description here
Source: tkaviation.net

I suspect it's related to the fuel system, but it's only found on the left wing (see the yellow circle, not the pitot-tube). I haven't been able to find the right keywords to find anything about it.

I'm hoping to know its function and how it does it.

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  • $\begingroup$ The pitot tube is to the left of the strut. It is a fuel vent. You will often find fuel leaking out of it when the plane is parked on a slope. $\endgroup$ – JScarry Jan 20 at 4:37
  • $\begingroup$ @JScarry two of them? I've annotated the photo, though there was already a circle. $\endgroup$ – ymb1 Jan 20 at 4:44
  • $\begingroup$ Cessnas with a fuel selector that has a both position usually have one fuel vent. The Cessna 210 does not have a both position and the fuel vents are in the wing tip fairing on each side. $\endgroup$ – JScarry Jan 20 at 4:44
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I found a diagram from a 1978 Cessna 152 that explains the fuel system. Note the interconnected tanks. This one only has one vented cap, but because of leaking and water being trapped in rubber fuel bladders, most Cessnas have had their fuel caps replaced with Monarch caps, which are both vented.

Cessna 152 Fuel System

The checklist requires that you check the fuel vent for obstructions.

Cessna 152 Checklist

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  • $\begingroup$ Excellent thanks / Possible dumb question: If both caps are now vented, does that mean that the underwing vent tube has become vestigial? Or is it still needed for higher than ambient pressure (hence the pitot-like design)? $\endgroup$ – ymb1 Jan 20 at 20:08
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    $\begingroup$ @ymb1 I don’t know the answer to that but I think that the vent caps are there in case the main vent is clogged. That way fuel can still flow to the engine. Another example; my Cherokee has two under-wing vents and both caps are vented. The caps have a rubber fitting that will only open if there is lower than normal pressure in the tank. $\endgroup$ – JScarry Jan 20 at 20:23
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It's the fuel tank vent. It prevents forming a vacuum in the gas tank as it's drained, which would prevent further fuel flow to the engine.

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  • $\begingroup$ Thanks. How come it's on the left side only? $\endgroup$ – ymb1 Jan 20 at 4:48
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    $\begingroup$ The tanks are plumbed together so only one vent is necessary. $\endgroup$ – pericynthion Jan 20 at 4:57
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    $\begingroup$ @ymb there is a line that connects the two tanks. That’s one reason why it’s difficult to use fuel from only one tank in a Cessna. It’s also why, when you are refueling on a slope, you always want to fill the tank on the lower side first because otherwise the fuel on the higher tank drains to the lower tank and you have to go back and refill it. $\endgroup$ – JScarry Jan 20 at 4:58

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