be changed or supplemented. Consider the options shown in Section 5.1.6.
7.4.2.2 Option a) More Intensive Visual Inspection Change C-CHECK inspection to DETAILED instead of GENERAL VISUAL. The completed DTR Check Form is shown on Page 7.0.19. The values are derived as in 7.4.2.1. Note that the fourth C-Check Detailed inspection would supersede the D-Check Detailed inspection.
The ΔDTR value cannot be increased by doing an inspection twice. Therefore, the D-Check Detailed inspection is removed from the form. The TOTAL DTR has increased to 2.3, but is still less than the REQUIRED DTR of 4.
Original D6-82669 7.0 DOCUMENT USAGE
7.4.2.3 Option b) Inspection Interval Reduction Change C-Check inspection interval to N = 1,500 flight cycles. The completed DTR Check Form is shown on Page 7.0.20. The values are derived as follows: Detailed inspections must provide ΔDTR = 4. Taking cuts across the detailed curves for Direction 1 and 2 at N = 1,500 flight cycles, ΔDTR (Direction 1) = 2.0 and ΔDTR (Direction 2) = 2.0. Total DTR = 2.0 + 2.0 = 4 which meets the required DTR exactly. This option will normally be limited
by practical considerations.
7.4.2.4 Option c) Additional Inspections from Other Zones or Directions
The SSI is hidden internally; therefore, no other inspections are currently available. All available zones and directions are being used. Option c) is not applicable for this SSI.
7.4.2.5 Option d) Use of Appropriate NDT Procedures
Change D-CHECK inspection method for CHORD to Low Frequency Eddy Current (LFEC) through skin
(Direction 3).
The completed DTR Check Form is shown on Page 7.0.21.
The visual inspection values are derived as in Section 7.4.2.1. Note that the DETAILED inspection of
the skin is overridden by the LFEC inspection. Both inspections could be considered valid if they were
conducted independently.
The values for the LFEC inspection are derived as follows:
SPAR CHORD, INSPECTION DIRECTION 3, LFEC
Since the inspection is conducted every D-Check, enter D under CHECK LEVEL.
Since all eligible airplanes are inspected, enter 100 under % PHASE Ro.
The D-check corresponds to 10,000 flight cycles, so enter 10,000 under FREQUENCY, F.
All eligible airplanes are inspected N = F, so enter 10,000 under N= 100 F/Ro.
Enter ΔDTR vs. N chart at N = 10,000 flight cycles.
Read ΔDTR from 3-LFEC. Enter 7.1 under ΔDTR. Add the ΔDTR values (0.5 + 0.4 + 0.3 + 7.1 = 8.3)
and enter 8.3 for TOTAL DTR.
This value exceeds the REQUIRED DTR of 4. Therefore, the program is satisfactory. Since the
TOTAL DTR exceeds the REQUIRED DTR, the LFEC inspections can be changed to a phased
inspection program as explained in Section 7.4.2.6.
7.4.2.6 Option e) A Phased Inspection Program Change LFEC inspection at D-CHECK to a phased inspection program. The completed DTR Check Form is shown on Page 7.0.23. 中国航空网 www.aero.cn 航空翻译 www.aviation.cn 本文链接地址：737-300/400/500 补充结构检查文件 SUPPLEMENTAL STRUCTURAL INSPECTION DOCUMENT 1(21)
