CURRENT PROJECTS

Airworthiness Evaluation of Aging Small Airplanes

The “Airworthiness Evaluation of Aging Small Airplanes” is a two-phase research project sponsored by the FAA. The purpose of the project is to provide insight into the condition of a typical aged commuter aircraft through structural and systems non-destructive and destructive evaluation. The first two-year phase of the project involved the teardown of two high-time Cessna 402 aircraft. Both of these aircraft were inspected visually and with non-destructive methods including eddy current, magnetic particle and fluorescent liquid penetrant. The aircraft were then destructively evaluated through teardown and subsequent microscopic examinations. Damage found during this project was documented and characterized with the use of an optical microscope and a scanning electron microscope (SEM). All systems components were visually inspected, and then the hydraulic, fuel and oxygen lines were subjected to leak testing. The wiring of the aircraft was investigated visually and evaluated through non-destructive and destructive testing. Phase II of this project involves continuing to investigate the aging affects on commuter aircraft by teardown and inspection of two additional high-time commuters, possibly the Piper Navajo and Beechcraft 1900D. The information gathered during this project is being used by the FAA to assess the inspection programs of various aging aircraft and to provide owners and operators information on prolonging the life of aging aircraft through procedures mentioned in the “Best Practices Guide.”

Teardown Evaluation of Two T-34 Wings

The motivation for the “Teardown Evaluation of Two T-34 Wings” project lies in a 1999 fatal accident of a T-34. The accident occurred when the right wing separated due to metal fatigue, which resulted in failure of the front spar at WS 34 and failure of the rear spar at WS 66.

Since this accident, the FAA has issued airworthiness directives requiring inspections of the front and rear spars per a Raytheon service bulletin. The Raytheon repetitive inspection procedure uses an eddy-current method that requires removal of fasteners. The project will evaluate the current condition of two T-34 wings from a high-time aircraft. The evaluation will be accomplished through a destructive teardown and examination of the wing structure. The focus of the program is to detect and characterize cracks and corrosion currently existing in the structure. The corrosion will be characterized by type, depth and area, while the cracks will be characterized by length, orientation and failure mode. The set of wings purchased for the “Teardown Evaluation of Two T-34 Wings” project have a known spar failure. Because this project will be performed under the “Evaluation of Airworthiness for Aging Small Airplanes” grant, the results of this teardown evaluation will be provided as part of the final report for the complete research program.

B-52 Assemblies Teardown and Inspection

Sponsored by the B-52H Fleet Support group of the Boeing Company, the B-52 assemblies’ teardown and inspection project is being conducted in an effort to develop overhaul procedures of landing gear and flight control assemblies. Many of the components on the B-52H aircraft have received minimal maintenance, and most of these components have no overhaul/repair procedure in place. Manufacturing sources for many parts have diminished, and the only current source for replacement parts is the B-52G Model aircraft at the Aerospace Maintenance and Regeneration Center (AMARC). In order to prevent parts shortages, flight control and landing gear components are undergoing evaluation through the B-52 Functional System Integrity Program (FSIP). The teardown includes disassembly, cleaning, visual inspection, measurements to check for wear and elongation, non-destructive inspection (NDI) to check for cracks, reassembly and overall evaluation. This inspection documents component condition and provides recommendations for overhaul procedures where applicable. The results also provide information on the usability of retired B-52G parts as safe, reliable replacements on the B-52H aircraft.

Aging of Composite Aircraft Structures: Decommissioned Boeing 737 Tail

As more composite components are being certified and used on primary and “flight critical” secondary structures, a future need of the research community will be to investigate the aging aspects of these composite, non-metallic structures and to provide airworthiness assurance of these composite components as well. Composite tail structures from Boeing 737s, which were originally put into service in 1980, were recently decommissioned. With a horizontal stabilizer from the decommissioned 737 tail structures, the FAA-sponsored research focuses on providing insight into the aging aspects of composite aircraft structures. The initial phase of the research involves non-destructive inspections using standard and advanced methods. The second research phase consists of destructive evaluation and inspection of the structure including tests for material properties and moisture content, visual and microscopy inspection for debonds and skin porosity and thermal analysis, among others. Results of the material properties tests will be compared to the material’s original properties in an effort to characterize the effects of age on composites.

PROPOSED PROJECTS

Teardown and Inspection of F-16 Static Test Article

Sponsored by Lockheed Martin, this project will evaluate the structural integrity of an F-16C Block 30 type version 25 static test article (STA) by a comprehensive teardown and inspection. One objective of the teardown and inspection is to find any unexpected damage in inaccessible areas. The inspection will also examine areas with expected damage and confirm the extent of the damage. The teardown and inspection will be divided into component structural disassembly and inspection/metallurgical evaluation. The mechanical disassembly portion of the teardown inspection will involve the center, aft and forward fuselage along with the wings and vertical tail. The inspection portion will involve close visual, eddy current, ultrasonic, dye penetrant and detailed measurement inspections of the three fuselage sections, the wings and the vertical tail.

C-5A Component Disassembly and Inspection

Sponsored by the U.S. Air Force, this project proposal supports the teardown and inspection of major aircraft components from a C-5A aircraft. This project would include the substructure disassembly, cleaning and non-destructive evaluation (NDE) of major aircraft components, such as the horizontal stabilizer tie box front beam, removed from a retired C-5A aircraft. The NDE will be conducted on critical details from the surrounding structure, and it will include the following inspection methods: close visual, eddy current, fluorescent penetrant and magnetic particle. Inspection results will be provided to the Center for Aircraft Structural Life Extension at the Air Force Academy, who will perform a fractographic analysis on the details as well as a damage tolerance assessment on these components.

Evaluation of Dents and the Effects of Reforming Dented Panels in KC-135 Fuselage

This U.S. Air Force research project supports the development of new procedures for the evaluation and repair of dents in the Boeing KC-135 aircraft. In conjunction with the KC-135 System Program Office and the Center for Aircraft Structural Life Extension (CAStLE), the laboratory will take part in a study to determine the effects of dented panels and their repair in the KC-135 fuselage. Currently, the options available to repair a damaged panel include: (1) replacing the panel itself, (2) removing and hand forming the panel back to its original shape, or (3) leaving the dented panel intact on the aircraft. Current technical orders provide limited instructions for dealing with dent evaluation, location on the aircraft and repair procedures. Damaged skin panels in the crown and non-crown regions of the aircraft are handled differently by taking into account the material type of the skin (2024-T3 or 7075-T6 aluminum), the number of dents, dent width/depth ratios, and proximity to other aircraft structures. Although the practice of hand forming panels is common in the field, additional testing needs to be conducted in order to evaluate stress concentration and residual stress effects present in the panel after the hand forming is complete, single versus multiple dented panels, and curved versus flat panel structural testing. The laboratory will support the research effort through (1) fabrication and shipment of test specimens for structural testing by CAStLE and (2) performance of non-linear finite element analysis on test and aircraft fuselage panels. Analysis results will be compared with experimental test results in order to assess the effects of dents on stiffened fuselage panels.

B-52 Wing Structural Teardown and Inspection

Many B-52 aircraft have been exposed to severe operational environments during their lifetime. The B-52 Fleet Support group of Boeing-Wichita has used a disciplined approach, primarily through Programmed Depot Maintenance (PDM), for several decades to ensure airframe structural integrity. However, many critical structural details may be incurring damage that is currently below the minimum detection threshold for conventional non-destructive inspection methods. The objective of this project is to perform a destructive examination on a salvaged B-52G structure in order to identify damage that cannot be detected during normal PDM inspections. A thorough visual examination will be performed on critical structural details from the wings of retired B-52G aircraft. The critical details will be fully disassembled to the component level, and the components will then be visually inspected under optical magnification. If necessary, metallurgical examination will be performed using optical and scanning electron microscopes in order to characterize all cracks and corrosion found during the close visual inspection. Examination results will be used to evaluate the effect on structural integrity and service life if the damage (i.e., cracking and/or corrosion) were to go undetected.

Raytheon Starship Teardown and Inspection

As part of the research to investigate the aging aspects of composite, non-metallic structures and to provide airworthiness assurance of composite components as well, the FAA is sponsoring the teardown and inspection of a Beechcraft Starship aircraft. Similar to the tasks being performed on the 737 horizontal stabilizer, the first tasks will involve non-destructive inspections using standard and advanced methods. These methods will include using ultrasonic methods to identify porosity in the skins and debonding between the skins and underlying structure. Then, a destructive evaluation will be conducted including tests for material properties and moisture content, visual and microscopy inspection for debonds and skin porosity, and thermal analysis, among others. Results of the material properties tests will be compared to the material’s original mechanical properties to determine the degradation due to age and environmental factors.