Destructive Evaluation of Aging General Aviation Airplanes 2006-01-2409
Due to current economic conditions, aircraft companies of today are experiencing an increasing need for their fleets to maintain safe operation beyond their original design life. The result is a growing percentage of aging aircraft that must maintain their airworthiness by utilizing standard methods of inspection and repair. In order to determine if potential continuing airworthiness problems exist for the general aviation fleet as a function of the aging process, the Federal Aviation Administration (FAA) established a research program at the National Institute for Aviation Research, Wichita State University, to conduct destructive evaluations of aged airplanes. The intent of the program is to provide insight into the condition of a typical aged airplane and to see if a correlation exists between its maintenance history and current condition from a safety of flight perspective. To date, three airplanes, used in commuter service - a 1969 Cessna 402A, a 1979 Cessna 402C, and a 1975 Piper Navajo Chieftain - have been evaluated in the research program. In order to achieve the level of inquiry desired, the aircraft were assessed during two phases of research. The “Inspection Phase” included a survey of the maintenance records; non-intrusive visual inspection of the aircraft structure, systems, and wiring; and supplemental non-destructive inspections of critical structural areas. The “Teardown Phase” consisted of detailed structural disassembly; intrusive visual inspection of aircraft wiring and system components; close visual inspections of internal structure; microscopic examinations of suspect and critical structural areas; and fractographic analysis of selected cracks found during the examinations. Results of the teardown evaluations illustrate the typical condition of an aged general aviation aircraft and show how differences in operational environment impact the aircraft's airworthiness. While the teardown evaluations involved a comprehensive look at the airplane as a whole, including airframe, wiring, and systems, this technical paper presents the evaluation results on the airframe only. The results of the overall research program point to some recommended actions that may improve the continued airworthiness of aging general aviation airplanes. Some recommendations are specific to airplane model, while others pertain to the teardown evaluation research program itself and its use in future investigations into the aged general aviation airplane fleet. Detailed results of the program are documented in technical reports for the FAA, the Cessna Aircraft Company, and the New Piper Aircraft Company. These results provide valuable information to permit the continued safe operation of aging aircraft and give new insight into the field of aging aircraft research.