A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to all Short Brothers Model SD3-60 series airplanes was published in the Federal Register on August 4, 1999 (64 FR 42291). That action proposed to require repetitive inspections of the elevator trim control cables for signs of wear damage or broken wires; replacement of damaged or broken cables with certain new cables; and replacement of all 7x7 cables with 7x19 cables.
Comment Received
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comment received.
Request to Review Inspection Interval
One commenter requests that the proposed AD be revised to either delete the requirement to repetitively inspect to detect wear damage or broken wires of the elevator trim cables at intervals of 12 months, or extend the intervals to 24 months. (The proposed AD currently requires repetitive inspections at intervals not to exceed "12 months or 2,400 flight hours, whichever occurs first"). The commenter states that the cause of the cable degradation is the repeated operation/movement of the cables over small radius pulleys, which is a factor of flights and flight hours, not calendar time. The commenter also notes that the 2,400 flight hour interval does not correlate with 12 months for these airplanes, since most are operated at significantly less than 2,400 flight hours per year. The commenter also states that the current SD3-60 maintenance program does not specify inspection of the elevator trim cables at 12 months, and does not contain any inspection with a 12-month interval where numerous units are to be removed, as would be required in order to inspect the elevator trim cable circuit. The commenter states that Shorts Service Bulletin SD360-27-27, Revision 1, dated April 1, 1999, is in error in referencing Revision 8 of the maintenance program as containing such inspection intervals.
The FAA does not concur with the request to delete or revise the requirement for inspections at 12-month intervals. Service history has shown these cables to be susceptible to breakage earlier than anticipated. After several incidents in which segments of the elevator trim cable severed in flight, more frequent inspections of the cables have been deemed necessary in order to preclude such in-flight events.
Additionally, the inspection intervals in the proposed AD were intended to parallel normally scheduled maintenance for the majority of affected operators. Shorts Information Letter SD360-IL-199, Revision 1, dated April 1999, states that a review of the current maintenance program inspection intervals has resulted in the proposal to reduce this inspection interval from a "D-Check", which is equivalent to 4,800 flight hours or 2 years, to a "C-Check" interval, which is equivalent to the 2,400 flight hour or 12-month interval required by this AD. However, under the provisions of paragraph (c) of the AD, the FAA may approve an operator's request for adjustment of the compliance time intervals if data are provided to substantiate that such an adjustment would constitute an acceptable level of safety. The FAA has determined that the requirement for inspections at the intervals specified in this AD is appropriate to address the identified unsafe condition. No change is made to the final rule.
Conclusion
After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed.
Cost Impact
The FAA estimates that 45 airplanes of U.S. registry will be affected by this AD, that it will take approximately 20 work hours per airplane to accomplish the required cable inspection, and that the average labor rate is $60 per work hour. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $54,000, or $1,200 per airplane, per inspection cycle.
The FAA estimates that it will take approximately 75 work hours per airplane to accomplish the required cable replacement, and that the average labor is $60 per work hour. Required parts will cost approximately $4,500 per airplane. Based on these figures, the cost impact of the cable replacement required by this AD on U.S. operators is estimated to be $405,000, or $9,000 per airplane.
The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.
Regulatory Impact
The regulations adopted herein will not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.
For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and (3) will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."
List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.
Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:
PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows:
Authority: 49 U.S.C. 106(g), 40113, 44701.
39.13 [Amended]
2. Section 39.13 is amended by adding the following new airworthiness directive: