Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08 1 Challenges Associated with Implementing an Integrated Structural Health/Life Management System for Aerospace Structures J.P. Gallagher Consultant Retired ASC/EN, USAF

Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08 2 Integrated Structural Life Monitoring Ref: J.P. Gallagher et al., “Future Airframe Lifing Methods”, NATO AVT-125 report, RTO,, in press (2008) Prognosis (assessments or predictions) can take place on-board or off-board

Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08 3 Challenges for On-board Sensing Cracking in safety-of-flight critical structure typically occurs later in the airframe life, so on-board systems must last for the airframe’s lifetime (20-40 years) Airframe inspection system reliability is less than anticipated for multiple reasons - on-board systems may solve some issues The key to success – must have accurate and reliable models/systems for anticipating “surprises” –Unconservative answers cause structural losses –Can not cry wolf when no wolf exists Usage monitoring suffers due to lower budget priorities for upgrading/replacing equipment required to collect operational parameters that affect damage evolution

Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08 4 Cracking Damage Counts The bigger cracks in the population are those that are most likely to cause premature structural failure & dictate when maintenance action is required The Crack Size Population & Its Contributing Elements Evolve with Time Ref: J.P. Gallagher, ICAF 2007 High end, rare damage dictate structural maintenance for safety

Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08 5 Rogue Damage Does In Fact Exist Ref: J.P. Gallagher, ICAF 2007 Comparing Observed Damage to Anticipated Damage Evidence that bigger (rogue) cracks do exist comes from comparison of crack findings to anticipated crack growth life curves for each FCL

Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08 6 Challenges for Interpreting Sensor Info Damage in older aircraft systems does not always occur where it was anticipated nor according to the design scenario Cracking in lug regions found on F-22 FSFT Ref: Gen C.D. Moore, 2007 ASIP Conference These locations are considered “hot spots.” Where else might cracking occur that was not observed on the FSFT? Will the cracking observed in service have the same characteristics as that of the FSFT?

Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08 7 Concluding Remarks Structural health/life monitoring - a key component of Aircraft Structural Integrity Program (ASIP*) and the integrated structural health/life management system –Problem: Lack of attention to executing ASIP requirements and evaluating structural cracking problems –Cause: Priorities (capabilities vs. sustainment) and budget pressures –Result: Unanticipated loss in availability, aircraft groundings, higher sustainment costs (structural “surprises”) Recommendations for Targeted Action: –Ensure an integrated structural life monitoring capability plan supports the structural health/life management system –Demonstrate assessment and prediction via on-board hot spot sensors * See references for more detail on ASIP and its applications for sustainment

Prognosis of Aircraft and Space Devices, Components and Systems – J.P. Gallagher, 19 Feb 08 8 References 1.Department of Defense Standard Practice, Aircraft Structural Integrity Program (ASIP), MIL-STD-1530C, 1 Nov J.P. Gallagher, “A Review of Philosophies, Processes, Methods and Approaches that Protect In-Service Aircraft from the Scourge of Fatigue Failures,” Proceedings of the 24th ICAF Symposium 2007, Naples, IT (May, 2007). 3.L.M. Butkus, et al., “U.S. Air Force Efforts In Understanding And Mitigating The Effects Of “NDI Misses,” Proceedings of the 24th ICAF Symposium, Naples, IT (May, 2007). 4.J.P. Gallagher, et al., “Demonstrating the Effectiveness of an Inspection System to Detect Cracks in Safety of Flight Structure,” Proc. of the 10th DoD/FAA/NASA Aging Aircraft Conference, Palm Springs, CA (April, 2007) 5.J.P. Gallagher, “Damage Tolerant Aircraft Design and its Relationship to Inspections,” Presentation at the G.R. Irwin Memorial Conference, U. of Maryland, College Park, MD (March, 2007).