What happens if I run a fuel tank dry, whether accidentally, or on purpose for maximum range in cruise?
There is considerable information on this subject on the Avweb forum, which attempts to debunk many of the old wives’ tales on this topic.
If you maintain your fuel selector in good condition (meaning it is not tight), and you do it under appropriate circumstances (such as at altitude in cruise flight and with fuel in the other tank), there is nothing inherently “wrong” or “unsafe” about running a tank dry in our aircraft (carbureted or fuel injected). It is simply another point in the operating envelope that most people never try to explore (like most of the approved maneuvers that approach the performance limits).
Running a tank dry teaches you a great deal about your true fuel capacity for endurance flight planning. It enables you to measure your actual tank capacity, in terms of gallons and time. It can simplify some types of fuel tank and system maintenance (like a fuel level sender replacement or fuel drain repair). It enables you to safely achieve maximum range, when it is required, and with no guesswork. If you can fly 5.5 hour legs, and land with an hour’s fuel remaining in one tank, you can achieve a higher effective ground speed than a much faster plane that stops every three or four hours.
The fuel tank pickup point is above the lowest point in the tank. The fuel drain is close to (or at) the lowest point, in a reasonably level plane. Normal sumping practice and the finger screen assure that you won’t “pick up trash” when a tank empties. It isn’t as if your pickup screen goes any lower in the tank than it always is, just because the gas level goes lower.
Your aircraft had to demonstrate normal flow resumption and engine restart following fuel exhaustion, as a certification requirement. There is no reason for the momentary power interruption to cause alarm. You experience the same effect every time you close the throttle on short final (or during a “slam dunk” approach). People go up and fly without any engine at all, every day. A practiced response is all that is required, whether it happens on purpose, or accidentally. If accidental, hopefully it doesn’t occur at a bad time. As is usually the case, the biggest risk with any uncommon operating mode is the person doing the operating; not the airframe or systems. Now, I’ll be the first to admit that if the noise goes away unexpectedly, for a non-recoverable reason, I’ll join the ranks of the alarmed just like anyone else! Hopefully we will all deal with that effectively, should it ever happen to us. I’ll bet that you’ll be more calmly prepared to deal with it, if it isn’t the first time you have ever heard the engine stop producing power outside of a descent or landing.
There’s no need to go up and run a tank dry on every flight, just on principle, though I suppose it would help you better adhere to Bob Steward’s wise suggestion not to “tanker fuel”! If you do decide to reduce your normal fuel load, then happen to get caught with marginal fuel at some point in time, you’ll be pretty glad that you made yourself comfortable with both the max range engine settings, and with running a tank dry to achieve maximum range.
If you can’t or won’t get comfortable with this practice, by all means don’t perform it; just like any of the other less common operating modes of your airplane. Some people never get spin training. Some never go up and get aerobatic/unusual attitude training. Most of us never get all the possible ratings and
endorsements. I sure wouldn’t want to learn that someone crashed because they panicked, trying to do something they were not comfortable with and were not prepared for; whether practicing deep stalls or running a tank dry.