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
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 2 DELTA AIR LINES, INC.
Location of Interest: ZFS=52.267 Significant vibration issues 3 DELTA AIR LINES, INC.
Previous discovery/investigation 4 DELTA AIR LINES, INC.
2009 Presentation Review Delta „above and beyond‟ actions 5 DELTA AIR LINES, INC.
2009 Presentation Review SB, SSID development/validations 6 DELTA AIR LINES, INC.
Initial Inspection Results • 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 Not an „isolated incident‟ 7 DELTA AIR LINES, INC.
Feasibility Study • 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 1 st 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 2 nd 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 and optimization 8 DELTA AIR LINES, INC.
Reference Standards Hole diameter = 0.390” Hole diameter = 0.390” Bush to 0.199- 0.202” Bush to 0.199- 0.202” EDM Notch = 0.025” EDM Notch = 0.050” Standard Designed Hole diameter = 0.250” Hole diameter = 0.250” Bush to 0.199- 0.202” Bush to 0.199- 0.202” EDM Notch = 0.025” EDM Notch = 0.050” Reference Standard made 9 DELTA AIR LINES, INC.
Reference Standards Two standards made 1 st standard with EDM notches Hole L1 – 0.025” bushing & 0.025” EDM U6 U3 Hole L4 – 0.025” bushing & 0.050” EDM Hole U3 – 0.095” bushing & 0.025” EDM L1 L4 Hole U6 – 0.095” bushing & 0.050” EDM 2 nd standard without notches Hole L1 – 0.025” Al 7075 -T6 bushing U3 U6 Hole L4 – 0.025” Al 7075-T6 bushing L1 L4 Hole U3 – 0.095” Al 7075-T6 bushing Hole U6 – 0.095” Al 7075-T6 bushing 10 DELTA AIR LINES, INC. Different bushing thicknesses used
Complete Through-Bushing Inspection System 11 DELTA AIR LINES, INC.
Probes Rotational GRFEC Probe Unit RF2 ROT BH 200 Rotational Guide Probe Head Probe Carriage 12 DELTA AIR LINES, INC.
Feasibility Results 13 DELTA AIR LINES, INC. All EDM notches detected
Feasibility Results 0.025” Thick Bushing @ f= 1.0KHz No EDM 0.025” EDM 0.050” EDM 14 DELTA AIR LINES, INC. Impedance plane differences = good
Feasibility Results 0.095” Thick Bushing @ f = 1.0kHz No EDM 0.025” EDM 0.050” EDM 15 DELTA AIR LINES, INC. Even for thicker bushings
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 (Forcemate TM bushings) • Ready for next steps (POD study) toward AMOCs 16 DELTA AIR LINES, INC.
Questions? Thank you for your attention. 17 DELTA AIR LINES, INC.
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