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Printed page label not indexed. PDF page 24.
flush rivet heads extended through the entire thickness of the outer 0.036-inch sheet. A knife edge was created at the bottom of the hole which concentrated stresses. These stresses were cyclic with pressurization loads, and fatigue cracking ultimately occurred atOpen official document at PDF page 24NTSB AAR-89/03: Aloha Airlines flight 243, N73711
Printed page label not indexed. PDF page 26.
occur in the outer layer of skin along the lap joint because the outer layer contains a knife edge at each of the countersunk rivet holes. Furthermore, the fatigue cracking primarily is found in the upper row of the outerOpen official document at PDF page 26NTSB AAR-89/03: Aloha Airlines flight 243, N73711
Printed page label not indexed. PDF page 37.
rivets. The largest single fatigue crack in one direction measured 0.18 inch from the knife edge of the countersink. (See figure 6.) The longest total combined crack length in both directions across a rivet hole (end to end of theOpen official document at PDF page 37NTSB AAR-89/03: Aloha Airlines flight 243, N73711
Printed page label not indexed. PDF page 38.
CRITICAL a hm nm RIVET O O ROW O O O O ower SKIN Figure 6a.--Typical lap joint CRACK ORIGIN KNIFE EDGE YVAN! | | LW TYPICAL CRACK PROPAGATION Figure 6b.--Cross section of a rivet and skin |Open official document at PDF page 38NTSB AAR-89/03: Aloha Airlines flight 243, N73711
Printed page 50. PDF page 56.
and the rivets must carry the load. Because the lap joint rivets are countersunk, the knife edge created by the countersink produces a stress concentration that leads to fatigue cracking from the rivet hole. Therefore, while a disbonded lap jointOpen official document at PDF page 56NTSB AAR-89/03: Aloha Airlines flight 243, N73711
Printed page 71. PDF page 77.
the fail-safe characteristics of the fuselage. The fatigue cracking initiated from the knife edge associated with the countersunk lap joint rivet holes; the knife edge concentrated stresses that were transferred through the rivets because of lap joint disbonding. The disbOpen official document at PDF page 77NTSB AAR-89/03: Aloha Airlines flight 243, N73711