The structural failure on April 28, 1988 of a 19 year old Boeing 737, operated by Aloha airlines, was a defining event in creating awareness of aging aircraft in both the public domain and in the aviation community. This aircraft lost a major portion of the upper fuselage in full flight at 24,000 feet , near the front of the plane. Miraculously, the pilot managed to land the plane on the island of Maui, Hawaii. One flight attendant was swept to her death. Multiple fatigue cracks were detected in the remaining aircraft structure, in the holes of the upper row of rivets in several fuselage skin lap joints .
In the Aloha Boeing 737 aircraft, evidence was found of multiple site fatigue damage leading to structural failure. The resulting National Transportation Safety Board investigation report issued in 1989 attributed the incident to the failure of the operators maintenance program to detect corrosion damage. Earlier, in 1981, a similar aircraft had suffered an in-flight break-up with more than one hundred fatalities. Investigations pointed to corrosion accelerated fatigue of the fuselage skin panels as the failure mechanism.
Lap joints join large panels of skin together and run longitudinally along the fuselage. Fatigue cracking was not anticipated to be a problem, provided the overlapping panels remained strongly bonded together. Inspection of other similar aircraft revealed disbonding, corrosion and cracking problems in the lap joints.
Corrosion processes and the subsequent build-up of voluminous corrosion products inside the lap joints lead to so-called "pillowing", whereby the faying surfaces are separated. Special instrumentation has been developed to detect this dangerous condition . The aging aircraft "problem" will not "go away", even if airlines were to order unprecedented numbers of new aircraft. Older planes are seldom scrapped, and will probably end up in service with another operator. Therefore, safety issues regarding aging aircraft need to be well understood and safety programs need to be applied on a consistent and rigorous basis.
D. Miller "Corrosion Control on Aging Aircraft: What is being done ?", Materials Performance, October 1990, pp.10-11. (back)
J.F. Wildey II, "Aging Aircraft", Materials Performance, March 1990, pp.80-85. (back)
J.P. Komorowski et al. "Quantification of Corrosion in Aircraft Structures with Double Pass Retroreflection", Canadian Aeronautics and Space Journal, Vol.42, No.2, June 1996, pp.76-82.