Reading the description of various aviation out-of-fuel incidents on Wikipedia, a trend seems to emerge: An improper amount of fuel was loaded, and due to mechanical and/or human failure the error went unchecked; pilots ignored or silenced warnings on the assumption that the equipment was faulty; and it isn't until a fuel pump fails or an engine cuts out completely that the pilots take the situation seriously. But at that point it's too late—there's no fuel left and pretty soon the jet turns into a glider.

One way to add an additional layer of safety to this process would be to deliberately build the airplane so that it is significantly out of balance with no fuel loaded. One tank would be larger than the other, and in order to balance the aircraft it would be necessary to load enough extra fuel into the larger tank to land the aircraft safely on one engine in any likely low-fuel scenario. This additional fuel would act as a reserve tank, and be only available to the engine on the same side via gravity feed (as opposed to the rest of the fuel in the tank, which would be reachable by the fuel pump and thus available to both engines).

This way, no matter how many warnings the pilot ignored, one engine would be starved of fuel long before the other, causing a warning sign that's pretty hard to ignore—one engine shutting down completely. At that point, the pilot would be forced to make an un-fun but eminently achievable single-engine landing. Of course, in a low-fuel situation, having the aircraft out of balance would be a significant liability, so the unbalancing weight could be in the form of a water ballast tank on one side, which could be vented by the pilot as necessary. However, doing so would trigger an alarm that can ONLY be silenced by refilling the ballast, so as to prevent people from simply leaving the ballast empty.
-- ytk, Aug 16 2011

The major problem is that this would add a substantial amount of "dead" weight to the airframe, something that the design engineers strive sedulously to remove.
-- 8th of 7, Aug 16 2011


Not dead weight, but beer - to be consumed by the passengers during the flight.
-- hippo, Aug 16 2011


True, but that still beats "dead" passengers.

Assuming the airplane were still flyable when severely unbalanced, the ballast tank could be done away with by simply moving critical systems off center. And on a large airplane, some measure of rebalancing could instead be achieved by relocating passengers to one side of the aircraft in an emergency situation. Or, for that matter, by loading part of the luggage into a drop bay. This could even be turned into a plus for the airline—one of the perks of a premium fare could be a "best effort" guarantee that your luggage won't be jettisoned in an emergency.
-- ytk, Aug 16 2011


whats wrong with a camera? or a transparent oil tank so passengers and crew could see it?
-- pashute, Mar 29 2015


Cameras can be ignored. The fact that one engine has shut down cannot be.

Any mechanism that requires the pilot to actively check something has the potential to fail if the check is not performed or the results ignored for whatever reason. The idea here is for an early warning system that is guaranteed to alert the pilot to a low fuel situation, and is literally impossible to ignore or misinterpret.
-- ytk, Mar 30 2015



random, halfbakery