AD 2008-08-10

This AD is effective May 19, 2008.

The Director of the Federal Register approved the incorporation by reference of certain publications listed in this AD as of May 19, 2008.

For service information identified in this AD, contact Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207.

Nancy Marsh, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 917-6440; fax (425) 917-6590.

We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to all Boeing Model 737-100, -200, -200C, -300, -400, and -500 series airplanes. That NPRM was published in the Federal Register on August 31, 2007 (72 FR 50278). For certain airplanes, that NPRM proposed to require replacing the outboard stabilizing fitting and certain adjacent components of the main landing gear (MLG) support beam. That NPRM also proposed to require repetitive inspections for discrepancies of the outboard stabilizing fitting, walking beam hanger, and rear spar attachment, and corrective actions if necessary. For certain airplanes, that NPRM proposed to provide an alternative one-time inspection of the outboard stabilizing fitting for discrepancies and corrective actions if necessary, which would extend the compliance time for the replacement of the outboard stabilizing fitting. For certain other airplanes, that NPRM proposed to require performing a torque check of the aft pin of the outboard stabilizing fitting, and corrective actions if necessary.

We gave the public the opportunity to participate in developing this AD. We considered the comments received from the commenters.

Boeing asks that we change the description of the unsafe condition specified in the Summary and Discussion sections and in paragraph (d) of the AD. Boeing states that, Model 737-100, -200, -300, -400, and -500 airplanes are equipped with “A” and “B” hydraulic systems, and an additional standby hydraulic system. Boeing notes that fracture or disconnect of any of the structural parts specified in Boeing Alert Service Bulletin 737-57A1266, Revision 1, dated January 3, 2007 (referenced in the NPRM as the source of service information for accomplishing the actions), could result in damage to the “A” and “B” hydraulic system tubes and damage or jamming of the flight control cables. Boeing adds that the standby hydraulic system is protected from any damage from a fracture or disconnect of any of the structural parts because it is not in the affected area. Additionally, Boeing states that if the “A” and “B” hydraulic systems fail, the standby system and manual reversion enable control of the airplane. Therefore, Boeing asks that the description of the unsafe condition be changed as follows: We are issuing this AD to detect and correct that cracking, which could result in disconnection of the MLG actuator from the rear spar and support beam, and consequent damage to the hydraulic system, and possible loss of the “A” and “B” hydraulic systems and damage or jamming of the flight control cables. Damage or jamming of the flight control cables could lead to a possible loss of control of the airplane.

We agree with Boeing and have changed the description of the unsafe condition in the referenced sections as follows: “We are issuing this AD to detect and correct that cracking, which could result in disconnection of the MLG actuator from the rear spar and support beam, consequent damage to the hydraulic system, and possible loss of the “A” and “B” hydraulic systems and damage or jamming of the flight control cables. Damage or jamming of the flight control cables could result in loss of control of the airplane.” However, the Discussion section is not restated in the final rule; therefore, we have made no change to the AD in this regard.

Boeing asks that the term “titanium pin,” as specified in the Relevant Service Information section, be changed to “new pin.” Boeing states that the new forward fuse pin is made from 15-5PH CRES stainless steel. Boeing also asks that the word “components,” also specified in the Relevant Service Information section, be changed to “fuse pin” to avoid ambiguity or possible confusion.

We agree with Boeing that its suggested changes clarify the language; however, the Relevant Service Information section is not restated in the final rule. In addition, it is not necessary to further change the body of the AD because we already required “new components” for replacement parts. Therefore, we have made no change to the AD in this regard.

Air Transport Association (ATA), on behalf of one of its members, United Airlines (UAL), asks that the compliance period for paragraphs (g) and (h) of the AD be changed from 36 to 48 months to align with UAL's Model 737 heavy maintenance visit. The commenters' state that the work defined in the NPRM will require jacking and defueling of the aircraft, and extensive disassembly of the landing gear. The commenters add that these activities are conducive to depot-level maintenance only; the UAL heavy maintenance visit is done on a 48-month cycle.

We do not agree with the requests to revise the compliance time from 36 to 48 months. In Boeing Alert Service Bulletin 737-57A1266, Revision 1, dated January 3, 2007, the manufacturer recommended that the actions be done within 36 months after the release of the service bulletin. In developing an appropriate compliance time for this AD, we considered the serious nature of the unsafe condition as well as the recommendations of the manufacturer, the availability of any necessary repair parts, and the practical aspect of accomplishing the required inspection within an interval of time that corresponds to the normal maintenance schedules of most affected operators. In light of these factors, we have determined that the 36-month compliance time, as proposed, is appropriate. We do not find it necessary to change the AD in this regard. However, under the provisions of paragraph (p) of the AD, we will consider approving requests for adjustments to the compliance time if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety.

We have changed the paragraph reference in paragraph (n) of the NPRM for clarification. Paragraph (n) specifies that accomplishment of the replacement of the tube assembly before the effective date of this AD is acceptable for compliance with the replacement specified in paragraph (l) of the NPRM; however, the correct reference is paragraph (m) of this AD.

We reviewed the relevant data, considered the comments received, and determined that air safety and the public interest require adopting the AD with the changes described previously. We also determined that these changes will not increase the economic burden on any operator or increase the scope of the AD.

There are about 3,130 airplanes of the affected design in the worldwide fleet. This AD affects about 1,380 airplanes of U.S. registry.

For all airplanes: The replacement takes between 20 and 24 work hours per airplane to do, depending on the airplane's configuration, at an average labor rate of $80 per work hour. Required parts will cost between $3,658 and $4,272 per airplane, depending on the airplane's configuration. Based on these figures, the estimated cost of the replacement is estimated to be up to between $7,256,040 and $8,544,960, or between $5,258 and $6,192 per airplane, depending on the airplane's configuration.

For Groups 1 through 8 airplanes: The alternative inspection, if done, takes about 12 work hours per airplane to do, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the alternative inspection is estimated to be up to $1,324,800, or $960 per airplane.

For Group 9 airplanes: The general visual inspection takes about 2 work hours per airplane to do, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the general visual inspection is estimated to be up to $220,800, or $160 per airplane.

For Groups 1 through 5 airplanes that had steel pins replaced per the original issue of the service bulletin: The torque check takes about 7 work hours per airplane to do, at an average labor rate of $80 per work hour. Based on these figures, the estimated cost of the torque check is estimated to be up to $772,800, or $560 per airplane.

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. “Subtitle VII: Aviation Programs” describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in “Subtitle VII, Part A, Subpart III, Section 44701: General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

This AD will not have federalism implications under Executive Order 13132. This AD will not have a substantial direct effect 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.

For the reasons discussed above, I certify that this AD:

(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.

You can find our regulatory evaluation and the estimated costs of compliance in the AD Docket.

Accordingly, under the authority delegated to me by the Administrator, the FAA amends 14 CFR part 39 as follows:

1. The authority citation for part 39 continues to read as follows:

2. The FAA amends § 39.13 by adding the following new AD: