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Another outcome was the creation of the Advisory Circular (AC) 20-128A. Developed as a document applicable to Part 23 and Part 25 category aircraft, this AC was meant to publicly set out a compliance method concerning design safety measures taken to reduce the potentiality of hazards of an aircraft during the occurrences of auxiliary power unit rotor or uncontained engine failures (FAA, 1997). Certain items within the AC 20-128A did include, the location of the auxiliary power unit rotors and engines, safety analysis, accepted design precautions, and engine failure models (FAA, 1997).
ASSIGMENT 4.2: UNITED AIRLINES FLIGHT 232 TRAGEDY 10Also, since this accident notified regulatory authorities of the flaws in the most advanced inspection and manufacturing processes during that time, the FAA was prompted to work intensely with an array of industry groups and manufacturing companies (FAA, n.d.-a). This led the industry to strategize and develop a guideline that acknowledged the defects that may damage the structural integrity of high-energy rotors but also create a damage tolerance method with respect to the service life management and design of such rotors. Fundamentally, this was based on the NTSB recommendation to research emerging technologies in the field of non-destructive inspection to improve the reliability or automate the process (NTSB, 1990). In the end, the industry came out with the AC 33.15-1, providing non-mandatory information and guidance concerning the suitability and durability regulations of materials (FAA, 1998). Applicable to manufacturing titanium alloy high-energy rotor parts of an aircraft engine, the AC 33.15-1 also discusses areas of raw material conditions, melting and consolidation, disk forging, non-destructive testing, and successive VAR processes (FAA, 1998).Compounding on the ACs, the FAA also issued Airworthiness Directives (ADs) for both the CF6 engine series and the DC-10s. But two of the latest ADs were AD 91-15-03 and AD 95-14-06. For AD 91-15-03, issued in 1991, the purpose was to prevent aircraft damage and uncontained engine failure by replacing defective stage 1 fan disks in the CF6 series and requiring the use of the new eddy current inspections in the manufacturing processes (FAA, n.d.-b). While, the AD 95-14-06, required adjustments of the landing gear, hydraulic systems, and flight controls for DC-10s to ensure aircraft survivability if the flight control systems are damaged (FAA, n.d.-b).Finally, a significant outcome was the subsequent development of FAA initiatives that were not only aimed at the DC-10-10 and the CF6-6 engines but rather the global aviation
ASSIGMENT 4.2: UNITED AIRLINES FLIGHT 232 TRAGEDY 11industry. One main example of the multitude of FAA initiatives would be the formation of the FAA Titanium Rotating Components Review Team. Through this initiative/industry group, the personnel employed were committed to reviewing, collecting, and analyzing data in regard to thedesign, inspection, and manufacturing of titanium spools, rotor disks, and hubs in turbine enginesto improve overall aviation safety (Green, 2019).