The reason I have a fuel transfer LED (and it's just green and doesn't flash) is purely for information that the pump really is getting power, and that it shuts off automatically when it's supposed to, after about three minutes. I agree that the automatic level switch makes a lot of sense, but I've got two dead fuel level sensors in two different tanks in my plane, both of which lasted a mater of weeks before they croaked, so I hope folks choose better than I did in that regard (Compac Engineering).
I'd be tempted to find an automotive (either factory or aftermarket) level sensor that has the extra connection for a "low fuel" light, and use that to trigger a warning light, just like in your car. But I've found in my plane that I never, not once, ran the main tank out of fuel, for the reasons Matt mentioned....the fuel gauge in the header tank is something I glance at quite often, and when it drops to the point that it could hold another couple of gallons, I shoot it over there. The "fuel transfer" light is just to let me know if the pump is receiving power or not (and hopefully working). That's not to say that I didn't know what the gauge looked like when it was dead empty. Part of my annual inspection is to prop the tail up to flying angle and run the fuel out, to make sure the gauge is still accurate, and that I know how it looks just before it gets there. As much as I don't like fuel in the cabin, I have to admit that the Swift has a fuel system I could like in a KR. It has an aluminum "header" box that holds about a quart of fuel, right under the seats. It has a standpipe sticking out the top, into which a cork float twists a magnet that acts on a gauge that sticks out between the seats (like a boat fuel tank, I'm told). This aluminum box is plumbed to the two wing tanks, always receiving fuel from both tanks by gravity, and the fuel is then pumped from the aluminum box to the carb by a mechanical and/or electric pump. Gravity means no such thing as fuel left in either tank when it finally runs dry. This way, only one water/trash drain is needed. It's remoted to a pull knob at the firewall via cable. The fuel outlet runs through a large fine screen before it can be sucked out of the header and to the carb. Another advantage to this system is that replacing the gauge is easily done in minutes with four screws, from inside the cabin, and without even draining the fuel! Of course my Swift's gauge has been operating flawlessly for 65 years One of the many nice things about the EIS is the programmable fuel remaining. I have mine set to alarm at 2.3 gallons (more than a half hour at cruise), but then that is based on the assumption that I've been smart enough to empty the aux wing tanks into the header tank via fuel transfer. With the Swift system, that issue doesn't exist, and I'd only need two electric pumps (main and backup), rather than four (add a pump for each aux tank)... Mark Langford ML at N56ML.com website at http://www.N56ML.com --------------------------------------------------------
