AD 97-03-14

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 certain Boeing Model 737-300 series airplanes was published in the Federal Register on August 28, 1996 (61 FR 44237). That action proposed to require a visual inspection to detect fatigue cracking, base trim, and upper flange over-trim of the pulley brackets of the aileron control cables. That action also proposed to require, if necessary, replacement of the pulley brackets with new pulley brackets, and replacement of the two button-head rivets with flush-head rivets.

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received.

Support for the Proposal

One commenter supports the proposed rule.

Request to Revise Statement of Findings of Critical Design Review Team

One commenter requests thesecond paragraph of the Discussion section that appeared in the preamble to the proposed rule be revised to accurately reflect the findings of the Critical Design Review (CDR) team. The commenter asks that the FAA delete the one sentence in that paragraph, which read: "The recommendations of the team include various changes to the design of the flight control systems of these airplanes, as well as correction of certain design deficiencies." The commenter suggests that the following sentences should be added: "The team did not find any design issues that could lead to a definite cause of the accidents that gave rise to this effort. The recommendations of the team include various changes to the design of the flight control systems of these airplanes, as well as incorporation of certain design improvements in order to enhance its already acceptable level of safety."

The FAA does not find that a revision to this final rule in the manner suggested by the commenter is necessary, since the Discussion section of a proposed rule does not reappear in a final rule. The FAA acknowledges that the CDR team did not find any design issue that could lead to a definite cause of the accidents that gave rise to this effort. However, as a result of having conducted the CDR of the flight control systems on Boeing Model 737 series airplanes, the team indicated that there are a number of recommendations that should be addressed by the FAA for each of the various models of the Model 737.

Request to Extend Compliance Time

The Air Transport Association (ATA) of America, on behalf of one of its members, requests that the proposed compliance time be extended from 18 months to four years. The ATA member indicates that the consequences of bracket failure are minimal since a dual control path exists. The commenter adds that, even in the event of total cable input failure on one side of the control path, control of the aircraft would not be lost. The commenter points out that the referenced service bulletin states that resultant cable slack will cause sluggish aileron control, which should be apparent to the flightcrew in the event of failure of a bracket. The commenter also states that the adoption of an 18-month compliance time would pose an unnecessary burden on operators, and that a compliance time of four years is adequate to address the unsafe condition. The ATA states that it does not view the identified unsafe condition as an airworthiness concern. However, in the interest of enhancing safety, the ATA requests that the rule be adopted with the extended compliance time.

The FAA does not concur. The FAA acknowledges that a dual control path exists, and that in the event of failure of a bracket, the second load path will allow operation of the aileron. However, under heavy flightcrew workload conditions, the ability of the flightcrew to control the airplane would be reduced; the FAA has determined that this poses a potential unsafe condition that must be corrected in a timely manner.

In developing an appropriate compliance time for the proposed inspection, the FAA's intent is that it be performed during a regularly scheduled maintenance visit for the majority of the affected fleet when the airplanes would be located at a base where special equipment and trained personnel would be readily available, if necessary. The FAA finds that 18 months corresponds closely to the interval representative of most of the affected operators' normal maintenance schedules. Additionally, since the service bulletin cited in this AD was issued in 1988, the FAA anticipates that a majority of the pulley brackets and rivets that require replacement have already been replaced. Finally, in light of the fact that the required actions take only one work hour per airplane to accomplish, the FAA is puzzled by the commenter's assertion that the 18-month compliance time imposes an "unnecessary burden" on affected operations. The FAA considers that an 18-month compliance time is appropriate and will provide an acceptable level of safety.

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

There are approximately 262 Model 737-300 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 169 airplanes of U.S. registry will be affected by this AD, that it will take approximately 1 work hour per airplane to accomplish the required actions, 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 $10,140, or $60 per airplane.

The cost impact figure discussed above is 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 thisAD were not adopted.

Should an operator be required to accomplish the replacement of pulley brackets and rivets, it will take approximately 15 work hours per airplane to accomplish those actions, at an average labor rate of $60 per work hour. Required parts will cost approximately $713 per airplane. Based on these figures, the cost impact of any necessary replacement action is estimated to be $1,613 per airplane.

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: