Inspection of Working Fasteners on the AH-64D Apache LongBow Helicopter Re-Manufacture Program

The AH-64D Apache Longbow Helicopter remanufacture program has presented unique issues for The Boeing Company-Mesa, Arizona; the U.S. Army; and the aircraft industry that are not normally associated with new-build aircraft. Once the AH-64A Apache aircraft are inducted at the Mesa facility, they undergo a pre-modification tear down, processing and evaluation of component serviceability. Typically, the AH-64A Apaches first submitted by the U.S. Army for remanufacture to AH-64D capability are those aircraft with the most flight hours in the Army’ inventory. The airframe has been thoroughly used and sometimes neglected during its field service, requiring evaluation of the structure for potential repair. An area requires constant attention throughout the induction, pre-modification, remanufacture and flight operation processes are the “working” of rivets within the airframe structure. A working rivet is normally found in rows and seldom found isolated. Working rivets are characterized by having loosened by the stresses invoked on the aircraft structure during ground run and flight operations. Also, they will begin to fret due to an already loose fit between the rivet and hole from the installation process. They also can become loose due to corrosion or from a combination of these factors. This paper shall discuss the possible cause and effect and the rework and repair required to bring the aircraft structure that has experienced working rivets, back to serviceability. Causes include a function of the design of the aircraft, as well as the manufacturing variability associated with the installation of the rivets that later become loose. The effects of working rivets include an aircraft that increasingly loses its structural integrity as more rivets work within a joint, most notably if the rivets are not identified and repaired. The rework and repairs completed by Boeing-Mesa are sometimes in response to repairs already accomplished by a repair facility or in the field. Rivets have been identified as working by U.S. Army technicians, or have caused damage by having been working and gone unnoticed. Field repairs are sometimes required to keep an aircraft flying. These are usually quick repairs that may move stresses to another area within the structure. These repairs can create difficulties, as the area may not have been intended to cope with this added stress. Sometimes these quick field repairs create more extensive work than if done at an authorized repair facility. Boeing-Mesa has also identified that a precise fit of the rivet shank to the prepared oversized hole is paramount to reducing the likelihood of the fastener working in the future. The discussion will also address documentation availability, specification and inspection criteria for the working rivet condition. Most notably, the paper will discuss the inspection and detection of the working rivets. Also, lessons learned from the discovery, disposition, action taken on the Apache and other helicopter programs, to confront the working rivet issue on the AH-64 fuselage and empennage will be discussed. An aircraft that is brought in for repair may require examination in the areas susceptible to working rivets upon receipt, after it is washed, while it is being repaired, and after it is test flown.