CFM Acoustical Panel Screws

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Acoustical Panel
Screws
Presenter
CFM56 Operators Conference – May 21 - 22, 2001 CFM Proprietary Data Unauthorized Disclosure Prohibited 2
First Step: EIS - 1997
• Forward acoustical panel bolt liberation
- Fan blade, panel & OGV damage
• Inappropriate panel assembly procedure at
production level
- Bolt torquing value
- 7.5 to 8.5 Nm instead of 9.5 to 10.5 Nm
- Lower than -5A model
- Assembly tool speed
- 600 rpm instead of 200 rpm
CFM56 Operators Conference – May 21 - 22, 2001 CFM Proprietary Data Unauthorized Disclosure Prohibited 3
• Corrective actions
- Improved values for bolt torquing sequence
- Forward & mid panel bolts: 9.5 - 10.5 Nm / 200 rpm
- Introduction at production level
- ESN779-282(DAC)&779-273(SAC)
- SB 72-213 issued, Jan 98
- At A or C-check opportunity and/or at shop level
- One time inspection and re-torquing
- AMM & ESM 72-23-00 updated
First Step: EIS - 1997
CFM56 Operators Conference – May 21 - 22, 2001 CFM Proprietary Data Unauthorized Disclosure Prohibited 4
• No post SB 72-213 reports from 1998 to 2000
• End of 2000, acoustical panel bolt looseness / liberation
with secondary damage
- Fan Blade L/E, OGV, panels, Fan abradable damage
- Several engines complied with SB 72-213
Second Step: 2000 - 2001
CFM56 Operators Conference – May 21 - 22, 2001 CFM Proprietary Data Unauthorized Disclosure Prohibited 5
• Screw degradation scenario understood
- Fretting initiation between screw head and panel cup
- Cup and screw head subsequent wear
- Panel beating against screw head
- Cup, anchor nut and screw damage
• No screw loosening
Second Step: 2000 - 2001
CFM56 Operators Conference – May 21 - 22, 2001 CFM Proprietary Data Unauthorized Disclosure Prohibited 6
• Main contributor - lack of grease under screw head
- Influences final tightening stress
- SB 72-213 Rev 2 issued Oct. 2000
- Grease application on screw head and threads
- Tool speed limitation: 200 rpm
- Repetitive inspection
- AMM updated
- ESM to be updated 2Q02
Investigation Results
Screw Head Lubrication Is Essential for Panel Tightening
CFM56 Operators Conference – May 21 - 22, 2001 CFM Proprietary Data Unauthorized Disclosure Prohibited 7
• Vibration
- CFM56-5B forward panel specificity: length / weight
- Sensitivity to engine vibration
- Bench test completed with instrumented panel
- Vibratory environment explored
- Forward panel more excited than mid panel
- New bench test scheduled to define the best panel
damping configuration
- Results targeted April 2002
Investigation Results
CFM56 Operators Conference – May 21 - 22, 2001 CFM Proprietary Data Unauthorized Disclosure Prohibited 8
• Assembly instruction reinforcement to ensure
proper assembly
- Grease application under screw head
- Production process sheet modified according to best
practices July 2000
- Introduced from SAC: 779870, DAC: 779975
Corrective Actions
CFM56 Operators Conference – May 21 - 22, 2001 CFM Proprietary Data Unauthorized Disclosure Prohibited 9
• SB 72-213 rev 3, clarifies torque repetitive check
procedure for all -5B engines
- Targeted 2Q02
• Expected benefit from application of assembly best
practices to be assessed
- Based on operators’ findings at first “A” check
- Evaluate efficiency and necessity to maintain SB 72-213 inspection
- Evaluate design change
- Focus Team early feedback: significant improvement from new
assembly procedure
• To date, no event reported on engines assembled with
best practices
Field Containment Plan

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CFM Acoustical Panel Screws