Design Factor of Safety for Aerospace

Aircraft and rotorcraft airworthiness standards require, generally, that structural
loading criteria are defined in terms of limit loads and ultimate loads. Limit loads
are structural loads which could be expected in service. Ultimate loads are equal
to limit loads multiplied by a prescribed factor of safety, typically 1.5, or 150%. By
definition, aircraft and rotorcraft structures must be able to sustain limit loads without
detrimental permanent deformation, and must be able to sustain ultimate loads without
failure. Essentially, the structure may bend permanently at ultimate load, but must
not break. Federal regulations often require a number of different factors of safety
for certain components and structures, which often exceed the 150% factor. For example,
certain critical hot air balloon structures must be designed to a 500% factor
of safety! All Wipaire, Inc. FAA certified aerospace structures are either analyzed or
tested considering the required factors of safety in order to show compliance with Federal
airworthiness standards.