Originally Posted by
SeenItAll
If lack of fuel in the wings causes them to break off, how did the Gimli glider or the Air Transat planes that ran out of gas in the air land successfully? And does this mean that Avianca at JFK really crashed from the wings snapping off and not from fuel exhaustion?
Well, by definition, those aircraft, with
complete fuel exhaustion, had no fuel in the center (fuselage) tank either. It is not so much a lack of fuel in the wings, but a lack of fuel in the wings
while still having substantial fuel weight in the fuselage, that puts one in more danger.
There
are aircraft that carry
no fuel in the wings,
ever (not enough room - F-104, B-47, Short 330/360, and of course any helicopter ever built
)
Plus, there is the concept of "margins." We may have less
margin for high-G maneuvers/events without fuel in the wings. That is not the same as
zero margin at all times.
Scenario - a flight over the Atlantic/Pacific, and for some ungodly reason all the pumps in the center tank fail before it empties. Choices - ditch, or burn off wing fuel to divert. The aircraft won't immediately fall out of the sky, but the pilots would (or should) know they would have progressively less margin for turbulence or manuevering stress, and treat the aircraft tenderly until safely down.
It is good policy to fill the wing tanks first and empty them last. It keeps down the immediate stresses and reduces fatigue over the life of the plane. In some cases (heavy lifters, always loaded to MTOW or MZFW) it will be more critical than in others.