After spending way too much time getting our fuel caps right on our 112, it got me thinking about the design of the fuel caps. I know that the Commander was certified under a higher standard, and part of that certification is the anti-siphoning system on our fuel caps (we loose a cap, and the fuel is not immediately sucked out in flight). This is done with the flapper valve. The cap is attached to this flapper valve, in the case of our 112 with a quarter turn assembly (I understand there is a newer style screw in type..).

In seeing the number of posts that have in one way or another related to fuel caps, my question is why is this system designed this way? It seems that a “standard fuel cap” could have been utilized, and the flapper valve also put in, but independently of the fuel cap. In other words, it would seem very possible to retro-fit a Bonanza with a flapper valve, but still utilize the existing fuel cap. Or an Arrow, etc.

I realize there is nothing we can do about this, but still I’m curious why the flapper has to be attached to the cap.