The effect of airplane size on occupant crash loads has been demonstrated using beam finite element models of Boeing 737-400 and 747-400 airplanes. For the impact survivable accident conditions investigated, it was shown that the 747-400 airplane transmitted a significantly lower level of occupant impulse than the 737-400 airplane. The studies showed that the 747 fuselage structure, though stronger than the 737, permits more deformation to occur over a longer time period. For the cases studied, the results showed that the 747 crash loads were only 1/3 to 1/2 of the crash loads generated for the 737.
The studies indicate it may be impossible to generate the currently specified FAR 25.561 and 25.562 crash loads in impact survivable accidents for the 747 and larger aircraft. As the external crash impact loads increase, crushing of the fuselage structure limits the internal crash loads to less than the current FAR requirements. As a result, larger airplanes such as 747 are required to carry an unnecessary weight penalty.
The crash models were developed using the ABAQUS program's nonlinear structural dynamics features. In this paper, the modeling approach is discussed, results are presented, and recommendations for further modeling improvements are made. The modeling technology was validated by analyzing to the 737-400 accident at Kegworth, England on January 8, 1989.
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