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Factors of Safety Related to Structural Integrity

The concept of structural safety as presently applied by the military airworthiness
authorities of the main NATO-Member-Countries has proven satisfactory, though being far
from having a rational basis.
Before this background, a Sub-Committee of SMP established a Questionnaire (see
chapter 1), asking the military authorities for all numerical factors applied to
ensure structural safety of aircraft. The answers given are condensed in chapter 2
of this report, including the results of personal discussions between coordinators
and nominated representatives of the authorities. The precis of the round table discussion
as well as an evaluation of answers and discussion are included for reasons of completeness.
From the evaluation it may be concluded that there exists a considerable amount of
agreement with respect to the Factors of Safety and their application. 0n the other hand,
some disagreements and different interpretations have resulted. Thus this report forms
a basis for discussing the disagreements in order to achieve a higher degree of conformity
between the authorities of the NATO-Countries with regard to structural safety and
reliability.
During the 46th SMP-Meeting, Spring 1978, the two coordinators presented a first
draft of the Questionnaire which was discussed in detail by the Sub—Committee. The final
version of the Questionnaire as laid down in the following paragraphs was distributed
to the airworthiness authorities through cover letter dated 15th Nov. 1978 (see 1.4).
The progress made with respect to determination of aerodynamic derivatives, loads,
stresses and deformation during the last decades together with the fact that there exists
a lack of rational basis for the Factors of Safety Concept presently applied to the
design of airvehicles, brought about a discussion of changing the structural safety
concept and the factors involved within AGARD-SMP some three years ago.
To condense these discussions AGARD-SMP formed an ad hoc group of Panel Members and
later a Sub-Committee. In Fall 1977 three pilot papers contained in AGARD—Report NO- 661
“Factors of Safety"addressed the different aspects to be envisaged, and showed up incon-
sistencies of the present concept as well as means and methods for permissible changes and
examples of the outcome.