The choice of smaller initial damage must be justified either through an NDI demonstration or a proof test.  The NDI demonstration program is described in JSSG-2006 paragraph 4.12.1.a.  The program must be formulated by the contractor and approved by the Air Force and must verify that, for the particular set of production and inspection conditions, flaws will be detected to the 90% probability level with 95% confidence.

Where no other means of NDI is available or where it is cost effective, the proof test can be an effective means of screening structure for flaws.  Proof testing generally has been successful for the more brittle materials which exhibit plane strain fracture behavior (e.g. high strength steels) and for small structural components.  The application of proof testing to complete airframe structure in the USAF has been somewhat limited.  The notable exception has been the cold proof tests (-40° F) of the F-111 aircraft to clear the D6AC steel wing carry-through and appendage components for flight usage. 

In general, proof testing has only been used on major airframe components as a last resort to allow operation (usually restricted) until extensive modifications are made to the structure (e.g. wing reskin modification of the B-52D).  In deriving estimates of the initial flaw size associated with the proof test conditions, approved upper-bound fracture toughness values shall be used for the materials under proof test conditions.  Section 3 also presents more information on the proof test concept.