KLM Fleet Services

KLM Comments on NPRM 2008-NM-093-AD: Docket No. FAA-2008-1071. Ref: Boeing SB 747-53A2478 R1 KLM expects a huge economic impact from the proposed AD due to 1/ the restricted compliance time for the initial inspection required by paragraph (i) (1) of the AD: for 25 out of 26 747-400's operated by KLM the threshold of 20,000 flight hours is passed and the grace period of 6,000 fligth hours after eff. date of the AD will be applicable. 2/ the low interval of 7,500 flight-hours for the repeat inspections required by paragraph (i)(1) of the AD. The above mentioned compliance time for the initial inspection and the repeat interval together with the current C-check interval of KLM 747-400's: approx. 12000 flight hours/24 months will force that the actual inspections will have to be planned during A-checks. KLM inspection history: The inspections done per SB 747-53A2478 R0 on all KLM and Cargolux 747-400's (KLM uses 72 month repeat interval for the DI per SB 747-53A2478+ teflon re- application) have resulted in several findings of wear. However, all findings beyond SRM limits were found no earlier than the 3rd D- check (105,000 flight hours, 13,500 cycles max). Actually 5 a/c out of 10 a/c total (having their 3rd D-check) had skin wear beyond SRM limits. Those 5 a/c had accumulated approx. 90,000 flight hours and 11,000 cycles since new. All findings in the 1st D-check (35,000 flight hours, 4,500 cycles max) and the 2nd D-check (70,000 flight hours, 9,000 cycles max) were within SRM limits. These results justify a less strict compliance time for the initial inspection. KLM is of the opinion that an alternative inspection for the subject fuselage skin could increase the repeat interval: Instead of only a detailed visual inspection: Perform a detailed visual inspection + surface HFEC inspection (per SB fig. 3 step 2 instructions) of both the blended and not blended skin in both section 46 and section 48. The much lower detectable crack length for the surface HFEC inspection justifies the increase of the repeat interval from the proposed 7,500 flight hours to an interval of 12,000 flight hours which would be in line with KLM's C-check interval. Conclusion: For the reasons mentioned above, KLM proposes to change AD paragraph (i) table 1 as follows: For actions required by par. (i)(1) of this AD: Increase grace period to 12,000 flight hours after the effective date of this AD. For actions required by par. (i)(1) of this AD: change repeat interval into: 7,500 flight hours for the detailed visual inspection or 12,000 flight hours for the combined detailed visual + surface HFEC inspection.