Development of NDI Tools for Detecting Cracks in MD88 Vertical - - PowerPoint PPT Presentation

Development of NDI Tools for Detecting Cracks in MD88 Vertical Stabilizer Holes with Bushings

David Piotrowski Delta TechOps Principal Engineer

• Dr. Yushi Sun

IMTT John Bohler Delta TechOps Level III-ET

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Outline

• 2009 Presentation at ATA
• Inspection Results Update
• RFEC through bushings
• Desired instead of large repair
• Promising capability demonstrated
• Now at POD stage
• ADs 2011-15-01/2011-12-12
• AMOC required
• Summary

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Location of Interest: ZFS=52.267

Significant vibration issues

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Previous discovery/investigation

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2009 Presentation Review

Delta „above and beyond‟ actions

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2009 Presentation Review

SB, SSID development/validations

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• All visual inspections complete –no findings.
• All one-time x-ray inspections complete –no findings.
• Six aircraft targeted for early BHEC inspections –two aircraft cracked
• Previous damage or repairs noted in area (pulled fasteners, cracks, etc)
• Entire fleet is to receive combined BHEC, LFEC and HFEC at Letter Checks
• 31 aircraft found with LE „distress‟; Repaired
• 17 aircraft cracked (BHEC); repaired with bushings
• Bushing repair is preferred over cut-out and splicing the spar cap
• One aircraft found cracked at hole, 2 fasteners outside BHEC inspection area
• Boeing SB MD88-55-066 (VS to fuselage attach points) cancelled “the SB has

become invalid”

• Boeing SB MD88-55A067 Issued = AD 2011-15-01
• Boeing SB MD90-55A014 Issued = AD 2011-12-12

Initial Inspection Results

Not an „isolated incident‟

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• First tests were done with two sets of RFEC probe units and promising results

were seen from both of the sets

• There was unfinished work in the 1st run of the test – lack of no-notch bushed hole in the

test standard

• Specimen with no-notch holes was made.
• The test results has confirmed that the 2nd RFEC probe unit is capable of detecting the

0.025” and 0.050” long EDM notches made on the NDT test standard.

• However, effects from different hole-edge and Hole-hole distances were unknown.
• Next, the probe was tweaked to minimize the effects from hole-hole distance

variation and hole-edge distance variation. ‒ Results good

• Finally, the probe was modified to minimize noise from no-notch holes and to

maximize S/N ratio. The noise is primarily caused by that the no-notch hole diameters are about 0.002” – 0.003” greater than the diameters made in the notched holes.

• Frequency range of 0.4kHz to 10.0kHz

Feasibility Study

Feasibility and optimization

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Standard Designed

Hole diameter = 0.390” Bush to 0.199-0.202” EDM Notch = 0.025” Hole diameter = 0.390” Bush to 0.199-0.202” EDM Notch = 0.050” Hole diameter = 0.250” Bush to 0.199-0.202” EDM Notch = 0.025” Hole diameter = 0.250” Bush to 0.199-0.202” EDM Notch = 0.050”

Reference Standards

Reference Standard made

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1st standard with EDM notches

Hole L1 – 0.025” bushing & 0.025” EDM Hole L4 – 0.025” bushing & 0.050” EDM Hole U3 – 0.095” bushing & 0.025” EDM Hole U6 – 0.095” bushing & 0.050” EDM

2nd standard without notches

Hole L1 – 0.025” Al 7075-T6 bushing Hole L4 – 0.025” Al 7075-T6 bushing Hole U3 – 0.095” Al 7075-T6 bushing Hole U6 – 0.095” Al 7075-T6 bushing L1 L1 L4 L4 U6 U6 U3 U3

Two standards made

Reference Standards

Different bushing thicknesses used

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Complete Through-Bushing Inspection System

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Rotational GRFEC Probe Unit RF2 ROT BH 200

Rotational Guide Probe Carriage Probe Head

Probes

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Feasibility Results

All EDM notches detected

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Feasibility Results

Impedance plane differences = good

0.025” Thick Bushing @ f= 1.0KHz

No EDM 0.025” EDM 0.050” EDM

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Feasibility Results

Even for thicker bushings

0.095” Thick Bushing @ f = 1.0kHz

No EDM 0.025” EDM 0.050” EDM

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Summary

• Significant issue on MD80/90 tails
• Delta/Boeing collaboration crucial to industry safety
• Inspection Collaboration
• SB development
• SSID validation
• Proactive fleet actions at Delta
• On-going repetitive inspections
• Continued vigilance
• Find it early, using bushings instead of large repair
• Bushings need to be removed for visual, BHEC
• RFEC to the rescue!
• Extremely promising results from IMTT
• Potential other applications (ForcemateTM bushings)
• Ready for next steps (POD study) toward AMOCs

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Questions?

Thank you for your attention.