Excerpt from the NTSB report regarding wing spar failure in EWR accident,
"Boeing estimates that the MD-11 landing gear strut will bottom and cause the wing rear spar to
fail if approximately more than 1,500,000 ft-lbs of energy is transmitted into a single
MLG. At 13.5 fps vertical speed, 0.5 g vertical acceleration, and 8° roll angle, the accident
airplane’s right MLG experienced an energy input of 1,574,000 ft-lbs during the second
touchdown, which was 3.2 times the maximum certification energy and slightly greater
than the MD-11’s estimated ultimate capability.
The MDI/Boeing structural simulations of the accident sequence indicate that the
right MLG strut and outboard tires bottomed at the second touchdown. Energy not
absorbed by the landing gear was then transmitted to the right wing rear spar through the
right MLG attach points. A corresponding down load was introduced from the left wing
and fuselage, which produced additional torsional loads on the right wing. These torsional
loads then produced a shear overload condition in the right wing rear spar according to
MDI/Boeing simulations. Boeing stated that the MDI simulations indicate that the failure
most probably “initiated at the rear spar/bulkhead (trunnion) rib interface and progressed
through the primary wing box structure. As a result of this failure, the right MLG trunnion
moved substantially upward and aft with respect to the trap [trapezoidal] panel fitting.”
Thus, the Safety Board concludes that the energy transmitted into the right MLG during the second touchdown was 3.2 times greater than the MD-11’s maximum certificated
landing energy and was sufficient to fully compress (bottom) the right MLG strut and
cause structural failure of the right wing rear spar."
You're only as good as your last departure.