(1) A fatigue strength investigation in which the structure is shown by tests, or by analysis supported by test evidence, to be able to withstand the repeated loads of variable magnitude expected in service; or
(2) A fail-safe strength investigation in which it is shown by analysis, tests, or both, that catastrophic failure of the structure is not probable after fatigue failure, or obvious partial failure, of a principal structural element, and that the remaining structure is able to withstand a static ultimate load factor of 75 percent of the critical limit load factor at V
(3) The damage tolerance evaluation of §23.573(b).
(b) Each evaluation required by this section must—
(1) Include typical loading spectra (e.g. taxi, ground-air-ground cycles, maneuver, gust);
(2) Account for any significant effects due to the mutual influence of aerodynamic surfaces; and
(3) Consider any significant effects from propeller slipstream loading, and buffet from vortex impingements.
[Amdt. 23–7, 34 FR 13090, Aug. 13, 1969, as amended by Amdt. 23–14, 38 FR 31821, Nov. 19, 1973; Amdt. 23–34, 52 FR 1830, Jan. 15, 1987; Amdt. 23–38, 54 FR 39511, Sept. 26, 1989; Amdt. 23–45, 58 FR 42163, Aug. 6, 1993; Amdt. 23–48, 61 FR 5147, Feb. 9, 1996]