Airworthiness Directives; The Boeing Company Model 737 Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Supplemental notice of proposed rulemaking (NPRM); reopening of comment period.

SUMMARY:

We are revising an earlier proposed airworthiness directive (AD) for certain Model 737 airplanes. The original NPRM would have required repetitive inspections, lubrications, and repetitive repairs/overhauls of the ball nut and ballscrew and attachment (Gimbal) fittings for the trim actuator of the horizontal stabilizer; various installation(s); and corrective actions if necessary; as applicable. The original NPRM resulted from a report of extensive corrosion of a ballscrew used in the drive mechanism of the horizontal stabilizer trim actuator (HSTA). This action revises the original NPRM by adding airplanes to the applicability. We are proposing this supplemental NPRM to prevent an undetected failure of the primary load path for the ballscrew in the drive mechanism of the HSTA and subsequent wear and failure of the secondary load path, which could lead to loss of control of the horizontal stabilizer and consequent loss of control of the airplane.

DATES:

We must receive comments on this supplemental NPRM by May 16, 2011.

ADDRESSES:

You may send comments by any of the following methods:

• Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
• Fax: 202-493-2251.
• Mail: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590.
• Hand Delivery: U.S. Department of Transportation, Docket Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

For service information identified in this proposed AD, contact Boeing Commercial Airplanes, Attention: Data & Services Management, P.O. Box 3707, MC 2H-65, Seattle, Washington 98124-2207; telephone 206-544-5000, extension 1, fax 206-766-5680; e-mail me.boecom@boeing.com; Internet https://www.myboeingfleet.com. You may review copies of the referenced service information at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington. For information on the availability of this material at the FAA, call 425-227-1221.

Examining the AD Docket

You may examine the AD docket on the Internet at http://www.regulations.gov;; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this proposed AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Office (telephone 800-647-5527) is in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

FOR FURTHER INFORMATION CONTACT:

Kelly McGuckin, Aerospace Engineer, Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 917-6490; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to send any written relevant data, views, or arguments about this proposed AD. Send your comments to an address listed under the ADDRESSES section. Include “Docket No. FAA-2008-0415; Directorate Identifier 2007-NM-256-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this proposed AD. We will consider all comments received by the closing date and may amend this proposed AD because of those comments.

We will post all comments we receive, without change, to http://www.regulations.gov,, including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this proposed AD.

Discussion

We issued a notice of proposed rulemaking (NPRM) (the “original NPRM”) to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to certain Boeing Model 737 airplanes. That original NPRM was published in the Federal Register on April 28, 2008 (73 FR 22840). That original NPRM proposed to require repetitive inspections, lubrications, and repetitive repairs/overhauls of the ball nut and ballscrew and attachment (Gimbal) fittings for the trim actuator of the horizontal stabilizer; various installation(s); and corrective actions if necessary; as applicable.

That original NPRM resulted from a report of extensive corrosion of a ballscrew used in the drive mechanism of the horizontal stabilizer trim actuator (HSTA) on a Model 757 airplane. Extensive corrosion of the primary load path ball bearings in the ballscrew assembly, if not corrected, could result in an undetected failure of the primary load path for the ballscrew in the drive mechanism of the HSTA and subsequent wear and failure of the secondary load path, which could lead to loss of control of the horizontal stabilizer and consequent loss of control of the airplane.

The ballscrew assembly on Model 757 airplanes is similar to those on the affected Model 737 airplanes. Therefore, all of these models may be subject to the same unsafe condition.

Other Relevant Rulemaking

We are considering additional rulemaking to address the identified unsafe condition on Model 757 airplanes.

Relevant Service Information

We have reviewed Boeing Alert Service Bulletins 737-27A1277, Revision 2, dated January 8, 2010 (for Model 737-600, -700, -700C, -800, -900, and -900ER series airplanes); and 737-27A1278, Revision 1, dated January 7, 2010 (for Model 737-100, -200, -200C, -300, -400, and -500 series airplanes). Boeing Alert Service Bulletins 737-27A1277, Revision 1, dated July 25, 2007; and 737-27A1278, dated May 24, 2007; were referred to in the original NPRM as the appropriate sources of service information for accomplishing the proposed actions. The revisions of the service information incorporate the following changes:

• Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010, adds Model 737-900ER airplanes to Group 2 of the effectivity, clarifies certain inspections necessary in Work Packages 1 and 2, and contains certain editorial changes.
• Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010, corrects the work instructions for the horizontal stabilizer trim actuator (HSTA) name plate identification information in Work Package 4 and clarifies certain inspections necessary in Work Packages 1 and 2 and contains certain editorial changes. In addition, the Horizontal Stabilizer Gearbox End Play Test is added because the gearbox backlash inspection is only identified in the airplane maintenance manual for Model 737-600, -700, -800, and -900 airplanes, but is also applicable to Model 737-100, -200, -300, -400, and -500 airplanes.

Actions Since Issuance of Original NPRM

Since we issued the original NPRM, we have changed this supplemental NPRM to include the revised service information, which expands the applicability of the original NPRM. We have also revised paragraph (h) of the original NPRM (paragraph (g) of the supplemental NPRM) to include credit for actions accomplished before the effective date of the AD in accordance with previous revisions of the service information.

Comments

We have considered the following comments on the original NPRM.

Request To Change Applicability

Boeing asked that we revise the applicability in the original NPRM to specify that it applies to all Model 737 airplanes instead of listing the minor models associated with the referenced service information. Boeing stated that this would avoid possible supersedure of the AD or certification maintenance requirements on future type certification programs.

We agree with the commenter for the reasons provided. We have changed paragraph (c) and the SUMMARY section of this supplemental NPRM to refer to all Model 737 airplanes.

Request To Clarify Procedures in Referenced Service Information

Air Transport Association (ATA), on behalf of its member Air Tran Airways (Air Tran) stated that the referenced service information is very difficult to interpret and cites examples from the service information. Air Tran stated that the accomplishment instructions specified in the service information contain language that is not specific and can not be used to make definitive determinations with regard to serviceability. Air Tran cited an example in Section 3.B.1.d.(2) of Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, which specifies “Large amounts of grease present * * *”. This language is not specific and open to a high degree of subjectivity. Air Tran added that other examples are in Section 3.B.1.n.(1) of this service bulletin, which specifies “majority of grease,” and in several places in Figures 1 and 2 of this service bulletin. Air Tran notes that the work instructions in Section 3.B. of Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, do not exactly match the instructions provided with the figures. Air Tran stated that having two sets of work instructions makes if difficult to follow, and could result in missed or partially accomplished work steps. Air Tran adds that Section 3.B.1.d.(8)(c) of this service bulletin provides instructions to check for obvious differences in thread shape between thread grooves “as given in CMM 27-41-01.” Air Tran noted that CMM 27-41-01 does not provide any procedure for checking for obvious differences. Air Tran also noted that the subject section should specify “refer to” rather than “as given in.”

Qantas has similar views to Air Tran and added that referring to the procedures specified by Air Tran for the on-wing inspection will be confusing to mechanics because the procedures are not designed to be completed on-wing. Qantas also suggested a better explanation and pictures be added to Section 3.B.1.n.(1) of Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, to quantify what is normal and what is an indication of a failure. Qantas noted that where there is evidence of a grease seal starting to fail, but no metallic debris, replacement of the unit should be deferred for up to five days, this would ease the burden of excess airplane down time. Qantas also noted that Section 3.B.1(o) of the procedures is not specified in the requirement table in paragraph 1.E. of Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007. Qantas suggested it be included in that paragraph. Qantas also asks that the detailed inspection criteria specified in Section 3.B.1.(d) of this service bulletin be clarified.

We agree that the procedures in the referenced service information should be clarified. We asked Boeing to revise the subject service information to provide better guidance and further clarification of the tasks that are specified. Boeing revised the service information as requested, as noted under the “Actions Since Original NPRM was Issued” and “Relevant Service Information,” sections of this AD and further clarification of the procedures is provided in those revisions, as well as the deletion of unnecessary procedures. Some portions of the task descriptions were left open to allow operators some latitude in accomplishing the tasks. We have revised this AD to refer to the new service information.

We agree that processes referred to by the commenters are not designed for on-wing or on-airplane inspections. Boeing provides clarification of the intent of these processes in Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010. Therefore, we have made no change to the supplemental NPRM regarding this issue.

Qantas also asked that Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, be revised. Qantas stated that the footnote at the top of page 10 of that service bulletin specifies “Boeing recommends that operators continue to perform lubrication tasks for the Stabilizer Trim Actuator given in Maintenance Planning Document (MPD) Section 1 and 737 AMM 12-22-41.” Qantas added that the MPD task requires lubrication every 1,600 flight hours or 8 months, and paragraph 3.B.1., of Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, specifies doing the same task every 1,600 flight hours or 12 months. Qantas noted that the Boeing 737 MPD and service bulletin tasks should not both be required. Qantas stated that the FAA or Boeing should clarify the lubrication tasks specified in that service bulletin, so operators can take credit for doing the task in accordance with that service bulletin.

We agree with the commenter. Boeing revised the service information specified in the “Relevant Service Information” and “Actions Since Original NPRM was Issued” sections of this supplemental NPRM. The referenced note has been removed and a new note added to Table 1 of paragraph 1.E., Compliance, of both service bulletins, specifying that accomplishing the lubrication task in Boeing Alert Service Bulletin 737-27A1277 or 737-27A1278 meets the intent of the lubrication task in the associated MPD.

Clarify Difference in Compliance Time Intervals

Boeing and US Airways asked that the compliance time interval specified in the original NPRM for the repetitive repair/overhaul be changed from 20,000 or 25,000 flight cycles to 20,000 or 24,000 flight hours (depending on airplane configuration) for Model 737-100, -200, -300, -400, and -500 series airplanes. Boeing stated that Tables 1 and 2 of Boeing Alert Service Bulletin 737-27A1278, dated May 24, 2007, specify the correct interval. Boeing adds that the subsection, Repetitive Repair/Overhaul, should be changed from “and thereafter at intervals not to exceed 20,000 or 25,000 flight cycles * * *” to “and thereafter at intervals not to exceed 20,000 or 24,000 flight hours * * *” US Airways reiterated the Boeing comment and recommends the difference be clarified.

We agree that clarification is necessary. The repetitive interval referred to in the original NPRM is incorrect. The correct interval of 20,000 flight hours or 24,000 flight hours (depending on airplane configuration) is specified in Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010. We have clarified the compliance time in this supplemental NPRM by referring to Boeing Alert Service Bulletin 737-27A1278, Revision 1, dated January 7, 2010.

Clarify Difference in Secondary Service Information Reference

US Airways asked that the secondary service information referenced in Note 1 of the original NPRM be clarified. US Airways stated that Note 1 refers to Linear Motion Service Bulletin 7901708, Revision A, dated July 26, 2005; however, the service bulletin supplied to US Airways from Linear Motion specifies Revision B.

We agree with the commenter. Since Revision B merely corrects a typographical error, Linear Motion Service Bulletin 7901708, Revisions A and B, both dated July 26, 2005, are acceptable. We have revised Note 1 of this supplemental NPRM accordingly.

Request for Credit for Accomplishing Previously Issued Service Information

US Airways referenced paragraph (h) of the original NPRM which specified “Actions done before the effective date of this AD in accordance with Boeing Alert Service Bulletin 737-27A1277, dated July 21, 2005, are acceptable for compliance with the corresponding requirements of this AD.” US Airways asked that a similar paragraph be added to give credit for previous accomplishment of Boeing Alert Service Bulletin 737-27A1278, dated May 24, 2007.

We agree with the commenter and have changed paragraph (g) of this supplemental NPRM to give credit for certain actions done in accordance with Boeing Alert Service Bulletin 737-27A1278, dated May 24, 2007.

Request To Clarify Compliance Times

Boeing asked that an additional statement be added to the compliance time in paragraph (g) of the original NPRM to clarify that it is dependent on the airplane configuration defined in the referenced service information. Boeing stated that the multiple recommended compliance times may be confusing to operators as there is no distinction of dependence on airplane configuration for the initial compliance times. Boeing suggested clarifying the compliance time by adding “(depending upon airplane configuration called out in the SB)” in parenthesis.

We agree with the commenter for the reasons provided. We have changed paragraph (g) of the supplemental NPRM to include the phrase “depending on airplane configuration” in parenthesis following the compliance time reference.

Request To Use Continuous Maintenance Program/Move Maintenance Planning Document (MPD) Tasks to Referenced Service Information

ATA on behalf of its member American Airlines reiterated the American Airlines comment that, except for accomplishing the installation of the strengthened ballnut retainers, all remaining requirements are part of the Model 737-800 continuous maintenance program and are subject to the type certification maintenance program rules. American Airlines stated that there are no historical indications for Model 737-NG airplanes that warrant an AD. American Airlines did not agree that the requirements in the AD that pertain to different airplane models with different designs and component manufacturers are strong enough to suspend parts of a continuous maintenance program. American Airlines added that if we have data not cited in the NPRM that substantiates an AD then the specified tasks should be removed from the continuous maintenance program. American Airlines concluded that continuous maintenance tasks such as inspection and lubrication typically have no terminating action by definition.

Air Tran supported the requirement to accomplish the installation of the strengthened ballnut retainers, but also requested that we allow the use of maintenance tasks and states that the lubrication requirements of Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, are similar to those in Boeing 737NG MPD Task 27-102-00 and the inspection requirements are similar to those in Boeing 737NG MPD Task 27-110-00. Air Tran added that the full requirements of Boeing 737NG MPD Tasks 27-102-00 and 27-110-00 should be incorporated into the AD and the subject MPD tasks removed from the Boeing 737NG MPD to avoid confusion. Qantas also asked that Boeing 737NG MPD Task 27-110-00-1 be incorporated into Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007. Qantas stated that if this task is included operators will not perform duplicate tasks from the Boeing 737NG MPD and referenced service information.

We infer that ATA, American Airlines, Air Tran, and Qantas are asking that the Boeing 737NG MPD Tasks specified in the original NPRM be removed, except for accomplishing the installation of the strengthened ballnut retainers, because all remaining requirements are part of the maintenance program. We do not agree with the commenters. We proposed mandating the maintenance tasks and intervals because of the criticality of maintaining the horizontal stabilizer control system; the consequences of not performing the maintenance tasks; and the service history attributed to lack of adequate horizontal stabilizer system maintenance on other airplanes. These maintenance actions can affect the safety of the airplane if they are not performed in a timely manner. We approve the maintenance review board report (MRBR), which is the basis for the MPD; the MRBR is an industry document that can only be changed by the MRB. The overlap is noted in Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, which identifies the MPD tasks. No revision to the MRBR is currently planned. Failure to perform the actions in this supplemental NPRM can lead to an unsafe condition; therefore, we have made no change to the supplemental NPRM in this regard.

Sun Country Airlines (Sun Country) stated that operators may need clarification on whether or not “restore,” as identified in Boeing 737NG MPD Item 27-108-00, meets the intent of the actions in the original NPRM. Sun Country stated that the repetitive actions specified in Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, are closely related to Boeing 737NG MPD Items 27-102-00, 27-108-00, and 27-110-00, in procedure as well as interval. Sun Country asked if operators following these MPD items can take credit for those already established maintenance requirements in lieu of the actions in the original NPRM. Sun Country added that because these MPD items already exist it would be advisable to change them to certification maintenance requirements (CMR) instead of mandating AD action.

We agree that certain requirements in Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, are similar to those tasks in the Boeing 737NG MPD. Boeing revised the referenced service information to address this issue. A note was added to the compliance tables in the service information stating that accomplishing the lubrication task in the service information meets the intent of Boeing 737NG MPD lubrication Task 27-102-00. We do not agree that the MPD Items should be changed to CMR requirements, because CMR requirements are established as part of the type certification of an airplane and are not initiated due to in-service issues. There are certain differences between the MPD tasks and the proposed requirements in the supplemental NPRM (e.g., inspections of the cable drum and electrical connector are not part of the actions specified in the referenced service information). We have made no change to the supplemental NPRM in this regard.

Request To Include Serial Numbers for Ballnut Tube Retainer Units

ATA on behalf of its member Air Tran noted that the identification of multiple airplane groups creates some confusion regarding which ballnut tube retainer units need to be installed. Air Tran asked that the AD identify the specific serial numbers of the units requiring modification to ensure that all affected units are covered.

We do not agree with the commenters. Operators can determine if the modification has been incorporated by verifying the part number on the component or doing a visual inspection of the ballscrew assembly. The proposed requirements in this supplemental NPRM prohibit the installation of affected unmodified ballscrews on certain airplanes. As standard practice, the airplane manufacturer addresses affected airplanes in the delivered condition in the effectivity of its service information. We have made no change to the supplemental NPRM in this regard.

Request To Review Paragraph 1.E. of the Referenced Service Information

Qantas asked that we review whether the desired level of inspection will be achieved using the current Boeing 737 CMM. Qantas stated that paragraph 1.E. of Boeing Alert Service Bulletin 737-27A1277, Revision 1, dated July 25, 2007, specifies an overhaul every 25,000 flight hours; Boeing 737 CMM 27-45-12 recommends the unit to be tested and disassembled only to the extent necessary to repair test failures. Qantas required vendors to strip the unit and complete visual and magnetic particle inspections.

We do not agree with the commenter. The intervals and tasks necessary for the lubrication, detailed inspection and overhaul/repair of the HSTA described in Boeing Alert Service Bulletin 737-27A1277, Revision 2, dated January 8, 2010, and proposed in this supplemental NPRM, address the unsafe condition of an undetected failure of the ballscrew primary load path and subsequent wear and failure of the secondary load path for affected airplanes. Due to these factors, we have determined that the desired level of inspection will be achieved when performing an HSTA overhaul. We have made no change to the supplemental NPRM in this regard.

Request To Extend Overhaul Life Limit

Qantas stated that by making the overhaul life limit mandatory the airline loses any flexibility in escalating the overhaul life based on service experience. Qantas added that there is considerable safety benefit in doing thorough overhauls with feedback of findings; one of the incentives for doing this is it includes the possibility of an overhaul life extension. Qantas noted that the original NPRM indicates an overhaul cost of $3,200; however, a recent procurement exercise by Qantas indicated the overhaul costs are about $18,000 per unit, not including any parts replacements. Qantas concluded that there is a considerable burden if extending the overhaul life is not permitted.

We do not agree to extend the intervals for maintenance tasks based on the commenter's service experience. In consideration of the safety implications, we determined that the compliance time for the maintenance tasks, as proposed, represents an appropriate interval in which the overhaul can be done in a timely manner within the fleet, while still maintaining an adequate level of safety. Although we acknowledge that the overhaul cost may be higher, the estimate in this supplemental NPRM is limited only to the cost of actions actually required by the AD, and is based on an estimate from the airplane manufacturer of the labor hours and subsequent cost necessary to accomplish those tasks. Therefore, we have made no change to the supplemental NPRM is this regard.

FAA's Determination and Proposed Requirements of the Supplemental NPRM

We are proposing this supplemental NPRM because we evaluated all pertinent information and determined an unsafe condition exists and is likely to exist or develop on other products of the same type design. Certain changes described above expand the scope of the original NPRM. As a result, we have determined that it is necessary to reopen the comment period to provide additional opportunity for the public to comment on this supplemental NPRM.

Explanation of Changes to This Supplemental NPRM

We have added a new paragraph (d) to this supplemental NPRM to provide the Air Transport Association (ATA) of America subject code 27; flight controls. This code is added to make this supplemental NPRM parallel with other new AD actions. We have reidentified subsequent paragraphs accordingly.

We have removed Table 1 of the NPRM from this supplemental NPRM. Instead, we have provided the full service bulletin citations throughout this supplemental NPRM.

Since issuance of the original NPRM, we have increased the labor rate used in the Costs of Compliance from $80 per work-hour to $85 per work-hour. The Costs of Compliance information, below, reflects this increase in the specified hourly labor rate.

Costs of Compliance

We estimate that this proposed AD would affect 1,641 airplanes of U.S. registry. The following table provides the estimated costs for U.S. operators to comply with this proposed AD.

The number of work hours, as indicated above, is presented as if the accomplishment of the actions in this proposed AD is to be conducted as new “stand alone” actions. However, in actual practice, the lubrications, detailed inspections, and overhauls are currently being done as part of normal airplane maintenance. The repair can be done coincidentally or in combination with the normally scheduled HSTA and ballscrew overhaul. Therefore, the actual number of necessary additional work hours will be minimal in many instances. Additionally, any costs associated with special airplane scheduling will be minimal.

We estimate the following costs to do any necessary repairs/replacements that would be required based on the results of the proposed inspection. We have no way of determining the number of aircraft that might need these repairs/replacements:

Authority for This Rulemaking

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.

Regulatory Findings

We determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would 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 this proposed regulation:

1. Is not a “significant regulatory action” under Executive Order 12866,

2. Is not a “significant rule” under the 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.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Incorporation by reference
• Safety

The Proposed Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 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.