Why do you need to turn on fuel pump when switching tanks ?

[Shadrach]

The reason I lost so much altitude was that I made sure first to establish a decent glide before going for the fuel selector. It also caught me by surprise, even though I was expecting it so I lost a few seconds. I didn't retrim for a slower and slower speed but just let it maintain cruise. Then with the LOP settings it apparently wasn't as simple as turn the selector and instantly roar back to life. Consider that the fact that my engine had suddenly died means my fuel lines were all full of air so there would be some delay. Setting everything for maximum fuel flow made sense to me to minimize the time it took to get the bubbles out. I think I'll stick with the "on below 1000 ft" rule so I can minimize the chance I'll find myself trying to sort this kind of thing out close to the ground. But  maybe not just for switching tanks.

Even without hitting the boost pump it takes less than 10 seconds to restart. I think it's about 5 secs from the moment the selector is turned. I run dry on long trips and I've never lost altitude, just a trivial amount of speed. It should be a no brain. it probably feels like an eternity to someone who's not used to it, but in reality it's a pretty low drama procedure.

[Guest]

I've only run a tank dry once in my Comanche.  The engine seemed to take an eternity to restart, with several seconds of surging which I attributed to the MT prop on a big engine.  Not really something I'll do regularly, but I wanted to know how the fuel pressure gauge would react to running out of fuel.  It's quite different than a carbureted Comanche.

Clarence

[ArtVandelay]

I'm surprised it just stops, I would expect it to start stumbling, and you would have enough time to quickly switch tanks before it completely stops.

[Hank]

I'm surprised it just stops, I would expect it to start stumbling, and you would have enough time to quickly switch tanks before it completely stops.

that's what my C did. Hiccup, smooth while I look for what happened. Hiccup, stumble, burp, smooth. Looked at clock, looked at selector--duh, forgot to change it 20 minutes ago! Switched it over, continued to run smoothly.

for those of you with fuel injection, your results will be different. You may wish to experience it once, on purpose at a safe altitude, just to see what it's like.