Description of Damage
An incident involving fuselage skin damage occurred on an aircraft. The skin panel opened, or 'flapped,' between body stations 1090 and 1110, peeling downward from stringer #4 left to stringer #5 left. The damaged area was located on the aft upper side, forward of the inlet for the #2 engine.
Examination Findings
A scratch or scribe mark was co-located with a longitudinal crack along stringer #4. Metallurgical examination determined that the crack had initiated at multiple origins along the score mark. The crack grew by fatigue through the thickness of the material. A striation count revealed that between 3360 and 5040 cycles of fatigue progression were present.
Conclusion Regarding the Score Mark
Examination of the score mark indicated that it was made by the use of marking tools during a repair process. The presence of the mark coincided with the location where the crack originated.