NDI of Composites, an Airline Perspective September 24, 2013

1. NDI of Composites, an Airline PerspectiveSeptember 24, 2013 Alex Melton Delta Air Lines Manager Quality Control NDT Programs

2. Composites Inspection Subsets • Legacy Composites – Honeycomb (Nomex), Metal Bond, Fiberglass, etc. • Typically found on flight controls, fairings, ray domes etc. • Usually limited to secondary structure • Some scheduled maintenance (Protective finish condition, tap test, visual etc.) • Some development taking place with IR (IR for water ingression, Flash IR) • Maintenance and Inspection requirements are fairly mature; Maintenance Steering Group 3 (MSG3) • Solid Laminate composites – Carbon Fiber Reinforced Plastic (CFRP) • Early applications in empennage primary structure; Utilization has grown to include fuselage, wings, and empennage primary structure on select aircraft • Robust materials requiring very little scheduled (routine) maintenance • Inspection technologies are a little more dynamic; lots of development taking place • Bonded Repairs to Primary Structure • Limited applications, but lots of potential • Unique inspection requirements

3. Honeycomb with carbon fiber face sheets.

4. Carbon Fiber Reinforced Plastic (CFRP)

5. Bonded doubler repair to horizontal stabilizer

6. Challenges at Delta • NDT inspectors in line check/environment primary function is not just NDT. • With Heavy Maintenance outsourced we no longer have dedicated NDT inspection crew’s whose sole function is NDT • Our inspectors are required to do many tasks: e.g.: Visual Inspection, RII, Run/Taxi & preflight after engine changes as well as certain levels of block visits (PSV, L-CK, H-CK, M-CK etc.) • These job duties all have their own training requirements that vie for resources and time spent on NDT • In some areas (line stations) NDT activity and variety can be a challenge • Many inspectors are qualified in multiple NDT methods • Composite NDI is a small (but growing) part of the overall NDI picture at the airline • Bond test equipment tends to be low usage when compared to eddy current and conventional UT equipment.

7. Challenges at Delta 7. Generally speaking, once composites go into service little Routine inspection is done to them other than visual, tap test inspection and checking protective finish condition. • Solid laminates tend to have little routine inspection. But like all structures can be subject to in-service damage • The robustness of composites and lack of scheduled inspections presents a unique training challenge • In ATL we have inspectors dedicated to back shops, but inspection of composites is not their sole function • Inspection methods on composites in the shop include Visual, X-Ray, Tap Test, TTU, IR, and Bond Testing • Hanger requirements are similar, though specific tasks very • With Heavy Maintenance work outsourced we rely on our Essential Maintenance Providers for a substantial portion of our composite inspection workload

8. Current Technology & Studies • Visual • Thermography(IR) for moisture ingression (honeycomb) • Tap Test • Automated Tap Test • Ultrasonic • Phased Array • TTU, Air Coupled UT • Free hand Resonance • MAUS Resonance • X-ray (conventional film and digital in ATL shop) • FAA-Sandia National Laboratories Airworthiness Assurance NDI Validation Center (AANC) Studies • Hail damage • Thermal degradation • Solid Laminate POD

9. Efforts • Large Area Inspections • Phased Array UT • Thermography • Resonance • Robotic Scanners/automation • MAUS in resonance mode • Sensors / Structural Health Monitoring / IVHM • Moisture/Crack/Embedded (delams/impact) • Active/Passive • G-11 SHM SAE Committee (AISC-SHM) • ARP 6461 (SHM Guidebook) balloted • Paradigm shift from defect-based to • material property based technologies • Predictive NDE • Bond-strength Photo courtesy of Sandia National Labs

10. Thermography (IR / TIR) • We have a successful Thermography program that started in 2002 on the A319/320 elevators and continues to this day • IR followed by RT to corroborate findings with a high degree of accuracy • OEM training was critical to successful implementation and iterative enhancement of the inspection program • A320 rudder inspection on our A/C and for customers in the 145 arena. • Elasticity Laminate Checker (ELCH) • Vacuum Loss (Not nondestructive) • UT Inspection of select areas • Thermography • Our capability on the A319/320 includes the oven method for removed elevators and on wing inspection with the heat blankets • In 2015 we will begin thermograhic inspection on the Delta A330 elevators, most likely this will be the on-wing heat blanket method

11. Resonance Ultrasound • We are working with Boeing on a prototype doubler installation on the MD88 and MD90 for a crack on the horizontal stabilizer skin panels. Once the metal to metal doubler is installed, we verify bonding with the Boeing MAUS V system using the resonance mode. • The strength restoring and damage containment attributes of this type of repair offer intriguing posibilities • Delta MD88’s have an overwing heater blanket installed at the wing root area forward of the engines to prevent upper surface wing root icing. These blankets are inspected during installation and in service with low frequency bond testing of the body area and the edges are inspected for disbonding using resonance UT. • Fixed Trailing edge resonance inspection, flight controls, etc.

12. Images of bonded doubler repair taken while operating in resonance modeThe ability to archive inspection images can be an advantage in select applications

13. TTU, Air Coupled UT, and Pulse Echo • We are investigating a program of scanning MD88 over-wing heater blankets with the MAUS V in resonance mode to create C Scan images that can be saved and used as a base line reference for future inspections. • The Curlin Air is used for inspecting composite core materials such as 737 thrust reversers and septum repairs on honey comb core material • Conventional UT is used in the pulse echo mode on solid laminates and acrylic cockpit windows after blending • The Through Transmission Ultrasound (TTU) is used to check for skin to core disbonds on items like fan cowling and Leading Edge slats that are rebuilt, also Trailing edge bonding of certain rudders (757) • Mitsui Woodpecker hasn’t gone into service yet due to reference standard fabrication, but will enter service laterthis year in ATL & MSP

14. UT Training • Delta has an internal 40 hr initial ultrasonic class that has a curriculum syllabus which is modeled after ATA 105 and other industry standards (NAS 410/EN4179, SNT-TC-1A, etc) • Topics on composites include: • Bondmaster operation • Pulse echo of solid laminates • Many UT Level 1 & 2 qualified inspectors participated in Sandia Labs Flaw Detection in Solid Laminate Composites Experiment • Thickness measurement of acrylic bonded windows • Through Transmission Ultrasound (TTU) • Lab work with test specimens

15. IR Training • Delta has an internal initial class that is modeled after ATA 105, Airbus & Snell infrared‘s training program. • Inspectors that complete this class get a qualification limited to inspecting for water ingression in composite components • We have a 2 year recurrent training program • Computer Based Training (CBT) with test the includes 3 IR images submitted to the IR Level 3 • With growth in the number of IR applications and changes in technology offerings we are actively considering expanding this training. • Realistic training aids present a challenge

16. Equipment • Conventional UT flaw detection equipment for solid laminates and composite core material • Stavely/Olympus Bondmasters 1000 and NDT Systems Bondascope 3100 for high & low frequency Bond testing of laminates and composite core materials • The Bondmaster is also used in the resonance mode • Curlin Air for non contact air coupled through transmission • Boeing MAUS system in the resonance mode for a prototype doubler bonded to the upper surface of 1ea MD88 and 1ea MD90 horizontal stabilizer. Also used in Eddy Current Mode • Mitsui Woodpecker Automated Tap Tester • Flir E60 BX IR camera used for water ingression on flight controls and miscellaneous honeycomb sandwich applications (Ray Domes, fairings etc.)

17. Avenues for collaboration Relevant knowledge, training, and equipment Inspectors Front-line (non-inspection personnel) Damage Reporting (BVID) Qualifications/Training/Certification AC 43- Repairs and Alterations to Composite and Bonded Aircraft Structure AC 65-CT, Development of Training/Qualification Programs for Composite Maintenance Technicians. Aerospace Recommended Practice document (ARP 1996-11 “Composite Repair NDT/NDI Handbook”) Importance of CACRC & A4A NDT Forum Organizations

18. B787Dark Blue – Carbon Solid LaminateLight Blue – Carbon SandwichGreen – FiberglassRed – AluminumYellow -Aluminum/steel/titanium pylons

19. Summary • Education • Different set of problems and challenges • Greater emphasis on task specifics and structural attributes • OEM training and input • Mindset/philosophy associated with new materials • FAA guidance • AC 43- Repairs and Alterations to Composite and Bonded Aircraft Structure • AC 65-CT, Development of Training/Qualification Programs for Composite Maintenance Technicians. • Importance of Industry Groups: CACRC & A4A NDT Forum • Composite Materials Handbook (CMH-17) • Record retention policies • Quality & retention time period, data volume • Liability • OEM Mandated technology adoptions • NDT Reference Standards & equipment • Cost-benefit analysis

20. Acknowledgements • Robert P. Hager • Delta Air Lines • Technical Specialist NDT • ASNT Level III – PT, MT, UT David Piotrowski Delta Air Lines Principal Engineer ASNT Level III – UT, ET, PT

21. Future Needs for Effective Use of Technology Questions? • Education • Different set of problems • Mindset/philosophy • FAA/OEM/Industry Guidance & Collaboration • AC 43- Repairs and Alterations to Composite and Bonded Aircraft Structure • AC 65-CT, Development of Training/Qualification Programs for Composite Maintenance Technicians. • Importance of CACRC & A4A NDT Forum • How to handle OEM IP ‘Hoarding’ & forced adoptions? • NDT Reference Standards • How to handle Records & record retention? • ‘Lifing’ • Quality & length of retention period • Punitive environment – liability • Cost benefit analysis for operators