AD 95-10-05

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, -400, and -500 series airplanes was published in the Federal Register on November 22, 1994 (59 FR 60095). That action proposed to require replacement of the horizontal stabilizer trim electric actuator.

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

One commenter requests that the proposed compliance time of 12 months for replacement of the actuator be extended to 18 months. The commenter states that timely accomplishment of the replacement is dependent upon the ability of BFGoodrich to quickly rework and return a fixed number of rotable actuator units. BFGoodrich has indicated that "loaner units" are not available, and that the initial retrofit/production units of the newer configuration will not be available to affected operators in time to allow replacement within the proposed compliance interval. Consequently, retrofit cannot be easily accelerated unless more rotable units are made available.

The FAA does not concur with the commenter's request to extend the compliance time for replacement. The FAA has been advised by Boeing that 75 loaner units have been made available to operators since the end of March 1995. These units are being manufactured to support the compliance time of this AD. (Boeing has advised that operators should contact Boeing Customer Service to arrange for delivery of loaner units.) In addition, the FAA has been advised that some operators have several spare units in-house which can be used as rotable units during the compliance period for the modification. In consideration of these factors, the FAA has determined that an extension of the compliance time is not warranted.

Two commenters request that the compliance time of proposed paragraph (b) be revised to allow installation of the unmodified actuators (having part number 10-62033-3) for a longer period of time after the effective date of the final rule. One of these commenters states that the inability to obtain spare units will be most severe in the early stages of the proposed retrofit; without more time to provide for spare modified units in the fleet, there is a high likelihood that airplanes could be grounded due to lack of airworthy parts. The other commenter states that the current operational procedures provide background information on stabilizer trim coasting, and that the current runaway stabilizer procedures in the Abnormal Procedures section of the Airplane Flight Manual effectively inhibit and limit an out-of-trim condition. In light of this, the commenter considers that the safety of flight would not be compromised by extending the compliance period by an additional 6 months.

The FAA concurs with the commenters' request. Although, as explained above, the FAA is confident that enough modified units will be available to all affected operators for replacement within the 12-month compliance time, there is a possibility that a modified unit may not be available, for example, in a situation where replacement is necessary and the airplane is in a remote location. For this reason, and the fact that adequate operational procedures are currently available to address potential out-of-trim conditions, the FAA considers that allowing unmodified units to be installed for a period up to 6 months after the effective date of the rule will not adversely affect safety. Such an extension also will ensure that no affected airplane will be grounded unnecessarily due to the unavailability of required parts. Accordingly, paragraph (b) of the final rule has been revised to allow installation of unmodified parts for 6 months after the effective date.

One commenter requests that issuance of the final rulebe delayed until a new electric motor assembly and accompanying service document is developed and available from the airframe manufacturer. This commenter states that the planned new assembly will do the tasks of the autopilot stabilizer trim servo and the stabilizer trim electric actuator; the motor does not incorporate directional clutches.

The FAA does not concur with the commenter's request to delay the rule. Delaying this action until after the release of the manufacturer's planned modification and service document is unwarranted, since parts are available at this time to address the unsafe condition within the compliance interval. However, the FAA may consider additional rulemaking once the new modification is developed, approved, and available.

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 with the changes previously described. The FAAhas determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.

There are approximately 1,448 Model 737-300, -400, and -500 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 590 airplanes of U.S. registry will be affected by this proposed AD. Accomplishment of the required replacement of the stabilizer trim actuator will take approximately 4 work hours per airplane, at an average labor rate of $60 per work hour. The cost of required parts is approximately $600 per airplane. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $495,600, or $840 per airplane.

The total 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 this AD were not adopted.

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. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89. § 39.13 - (Amended)

2. Section 39.13 is amended by adding the following new airworthiness directive: