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C-17 Globemaster III - Service Life

The original specification from McDonnell Douglas defined a service life of 30,000 hours. Modification programs will keep the aircraft in line with current and future requirements for threat avoidance, navigation, communications, and enhanced capabilities. These modifications should include global air traffic management (GATM) and automatic dependent surveillance to meet anticipated navigation requirements. Commercially available avionics and mission computer upgrades are being investigated to reduce life-cycle costs and improve performance. Also, upgraded communication systems to enhance worldwide voice and data (including secure) transmission will support command and control.

Currently, the C-17 airframes are not experiencing operational usage or fatigue that impacts their ability to achieve the 30,000 hour service lives. The missions that are flown are within the design assumptions/parameters of the aircraft. More specifically, the airframe was designed to withstand a higher percentage of airdrop, assault landing, and low level missions than has been experienced during C-17 operations. Because of that, the actual usage severity, in most cases, is less than predicted; therefore, there is no indication that C-17 airframes will be unable to meet or exceed the specified usage-based service life.

However, future changes in C-17 operations/deployment strategies could have an adverse effect on service life and would need to be considered during service life analysis by factoring weighted hours using the methodology. The PM monitors the critical aircraft components and assesses severity of usage on those components through the U.S. Air Force Aircraft Structural Integrity Program (ASIP), which is a preventive maintenance program of regularly scheduled inspections and replacement or repair of various elements of the airframe. This is accomplished on an aircraft by aircraft basis.

While the airframe did not experience a decrease in service life due to GWOT operations, the critical aircraft components experienced accelerated wear and tear due to GWOT operations. Exposure to the sand environment, extreme heat, evasive maneuvering, and steeper takeoffs and landings contribute to the increased wear and tear on the components of the aircraft, most notably the engine, landing gear, and flight controls. The wear and tear on these subsystems is mitigated by maintenance and repair, which drives up maintenance and repair/overhaul costs in order to maintain aircraft availability. In summary, the C-17 ASIP manages the fleet and identifies maintenance on the aircraft as needed to ensure each aircraft reaches its 30,000 hour service life.

Usage data at the asset level for C-17 aircraft is available in the Reliability and Maintainability Information System (REMIS), which holds usage data for Air Force aircraft. The C-17 program does not have an automated fatigue measurement tool that tracks fatigue on the airframes, so an estimate of fatigue must be applied in the methodology when operational and mission demands warrant that fatigue be incorporated within the calculation. Since the PMO has determined that fatigue currently has not posed a threat to the service life of the C-17 fleet since the aircraft are not operating beyond their design life operating boundaries, fatigue is estimated to be zero. C-17 engineers have noted that in the future, based on changes in mission profiles and operating conditions, fatigue could pose an impact on the service life and an estimate of the impact would need to be incorporated in the methodology.

Some programs have sophisticated fatigue tracking sensors and monitors that are used to track and monitor fatigue. For example, the Navy has a capability called the Structural Data Recording System (SDRS) that measures fatigue/strain, in terms of a metric called Fatigue Life Expended (FLE) or Total Life Index (TLI) based on the wing root and wing fold, on a variety of their attack (F/A-18) and fixed wing (P-3) airframes.

The C-17 program is experiencing changes in service life estimates that should be considered. For example, the Air Force Materiel Command has assessed that the C-17 program’s service life is 45,000 flight hours as opposed to the initial 30,000 flight hours projected by the original equipment manufacturer and PM based on fatigue and mission-type analysis.



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Page last modified: 05-02-2018 13:09:46 ZULU