00-6333. Airworthiness Directives; Boeing Model 737-100 and-200 Series Airplanes

AGENCY:

Federal Aviation Administration, DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

This document proposes the supersedure of an existing airworthiness directive (AD), applicable to certain Boeing Model 737-100 and -200 series airplanes, that currently requires inspections to detect cracking of the support fittings of the Krueger flap actuator; and, if necessary, replacement of existing fittings with new steel fittings and modification of the aft attachment of the actuator. That AD also provides for an optional terminating modification that constitutes terminating action for the repetitive inspections. This action would mandate accomplishment of the previously optional terminating action. This proposal is prompted by reports of cracking due to fatigue and stress corrosion of the support fittings of the Krueger flap actuator. The actions specified by the proposed AD are intended to prevent such cracking, which could result in fracturing of the actuator attach lugs, separation of the actuator from the support fitting, severing of the hydraulic lines, and resultant loss of hydraulic fluids. These conditions, if not corrected, could result in possible failure of one or more hydraulic systems, and consequent reduced controllability of the airplane.

DATES:

Comments must be received by May 1, 2000.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 99-NM-320-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9:00 a.m. and 3:00 p.m., Monday through Friday, except Federal holidays.

The service information referenced in the proposed rule may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124-2207. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington.

FOR FURTHER INFORMATION CONTACT:

Greg Schneider, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington; telephone [phone]; fax [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the proposed rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified above. All communications received on or before the closing date for comments, specified above, will be considered before taking action on the proposed rule. The proposals contained in this notice may be changed in light of the comments received.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this notice must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 99-NM-320-AD.” The postcard will be date stamped and returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 99-NM-320-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

On August 6, 1996, the FAA issued AD 96-17-04, amendment 39-9712 (61 FR 41957, August 13, 1996), applicable to certain Boeing Model 737-100 and -200 series airplanes, to require inspections to detect cracking of the support fittings of the Krueger flap actuator; and, if necessary, replacement of existing fittings with new steel fittings and modification of the aft attachment of the actuator. That action was prompted by reports of cracking due to fatigue and stress corrosion of the support fittings of the Krueger flap actuator. The requirements of that AD are intended to prevent such cracking, which could result in fracturing of the actuator attach lugs, separation of the actuator from the support fitting, severing of the hydraulic lines, and resultant loss of hydraulic fluids. These conditions, if not corrected, could result in possible failure of one or more hydraulic systems, and consequent reduced controllability of the airplane.

Actions Since Issuance of Previous Rule

When AD 96-17-04 was issued, it contained a provision for an optional replacement of the aluminum support fitting of the Krueger flap actuator with a steel fitting, and modification of the actuator aft attachment, which, if accomplished, would constitute terminating action for the required repetitive inspections. That optional modification was to be accomplished in accordance with Boeing Service Bulletin 737-57-1129, Revision 1, dated October 30, 1981, as revised by Notices of Status Change 737-57-1129NSC1, dated July 23, 1982; 737-57-1129 NSC2, dated April 14, 1983; and 737-57-1129 NSC 3, dated May 18, 1995. Revision 1 of the service bulletin contained a provision for operators to replace the existing aluminum support fitting of the Krueger flap actuator with a new aluminum support fitting. This action would mandate replacement of the aluminum support fitting with a steel fitting in accordance with Boeing Service Bulletin 737-57-1129, Revision 2, dated May 28, 1998. Revision 2 of the service bulletin specifies replacement of the aluminum support fitting with a steel fitting only, all references to replacement with an aluminum support fitting have been removed from the service bulletin.

Explanation of Requirements of Proposed Rule

Since an unsafe condition has been identified that is likely to exist or develop on other products of this same type design, the proposed AD would supersede AD 96-17-04 to continue to require inspections to detect cracking of the support fittings of the Krueger flap actuator on each wing; and replacement of any existing aluminum fitting with a new steel fitting and modification of the actuator aft attachment.

Differences Between Proposed Rule and Service Bulletin

Operators should note that, although the service bulletin recommends that the initial inspection be performed using a visual method and subsequent repetitive inspections be performed at regular maintenance intervals using an eddy current technique, this proposed AD would require that both the initial and repetitive inspections be accomplished using the eddy current method. The support fittings of the Krueger flap actuator on each wing are susceptible to stress corrosion cracking, and the crack growth rate for such cracking is unknown. The FAA finds that, if a visual inspection is accomplished to detect cracking of the support fittings, such cracking may not be detected in a timely manner to adequately address the unsafe condition. Therefore, the FAA has determined that an adequate level of safety for the affected fleet requires that both the initial and repetitive inspections of these fittings be performed at intervals not to exceed 3,000 hours time-in-service using an eddy current technique, which is a more reliable method for detection of cracking.

Operators also should note that this AD proposes to mandate, within 5 years after the effective date of this AD, replacement of any existing aluminum support fitting of the Krueger flap actuator on each wing with a new steel fitting; and modification of the actuator aft attachment, as described in Boeing Service Bulletin 737-57-1129, Revision 2, as terminating action for the repetitive inspections. Incorporation of this terminating action is described as optional in the service bulletin.

The FAA has determined that long-term continued operational safety will be better assured by design changes to remove the source of the problem, rather than by repetitive inspections. Long-term inspections may not be providing the degree of safety assurance necessary for the transport airplane fleet. This, coupled with a better understanding of the human factors associated with numerous continual inspections, has led the FAA to consider placing less emphasis on inspections and more emphasis on design improvements. The proposed modification requirement is in consonance with these conditions.

Cost Impact

There are approximately 727 Model 737-100 and -200 series airplanes of the affected design in the worldwide fleet. The FAA estimates that 270 airplanes of U.S. registry would be affected by this proposed AD.

The inspections that are currently required by AD 96-17-04, and retained in this proposed AD, take approximately 12 work hours per airplane (6 work hours per wing) to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the currently required inspections on U.S. operators is estimated to be $194,400, or $720 per airplane, per inspection.

The replacement and modification that is proposed in this new AD action would take approximately 88 work hours per airplane (44 work hours per wing) to accomplish, at an average labor rate of $60 per work hour. Required parts would cost approximately $12,226 per airplane. Based on these figures, the cost impact of the replacement and modification proposed by this AD on U.S. operators is estimated to be $4,726,620, or $17,506 per airplane.

The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the current or proposed 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 proposed herein would 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 proposal would not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

For the reasons discussed above, I certify that 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) if promulgated, 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 copy of the draft regulatory evaluation prepared for this action is contained in the Rules Docket. A copy of it may be obtained by contacting the Rules Docket at the location provided under the caption ADDRESSES.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Safety

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend 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 removing amendment 39-9712 (61 FR 41957, August 13, 1996), and by adding a new airworthiness directive (AD), to read as follows:

Boeing: Docket 99-NM-320-AD. Supersedes AD 96-17-04, Amendment 39-9712.

Applicability: Model 737-100 and -200 series airplanes, line numbers 001 through 813 inclusive, certificated in any category.

Note 1:

This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (d) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent possible failure of one or more hydraulic systems and consequent reduced controllability of the airplane, accomplish the following:

Restatement of Requirements of AD 96-17-04:

Repetitive Inspections

(a) Within one year after September 17, 1996 (the effective date of AD 96-17-04, amendment 39-9712), perform an eddy current inspection to detect cracking of the support fitting of the Krueger flap actuator on each wing, in accordance with Boeing Service Bulletin 737-57-1129, Revision 1, dated October 30, 1981, as revised by Notices of Status Change 737-57-1129NSC1, dated July 23, 1982; 737-57-1129 NSC2, dated April 14, 1983; and 737-57-1129 NSC 3, dated May 18, 1995; or Revision 2, dated May 28, 1998.

(1) If no cracking is detected, repeat the inspection required by paragraph (a) of this AD thereafter at intervals not to exceed 3,000 hours time-in-service.

(2) If any cracking is detected, prior to further flight, accomplish the replacement and modification specified in paragraph (b) of this AD.

New Requirements of This AD:

Terminating Action

(b) Within 5 years after the effective date of this AD: Replace any existing aluminum support fitting of the Krueger flap actuator on each wing with a steel fitting, and modify the actuator aft attachment, in accordance with Boeing Service Bulletin 737-57-1129, Revision 2, dated May 28, 1998. Accomplishment of this replacement and modification constitutes terminating action for the repetitive inspections required by paragraph (a) of this AD.

Note 2:

Replacement of the existing aluminum support fitting of the Krueger flap actuator on each wing with a steel fitting, and modification of the actuator aft attachment, prior to the effective date of this AD, in accordance with Boeing Service Bulletin 737-57-1129, Revision 1, dated October 30, 1981, as revised by Notices of Status Change 737-57-1129NSC1, dated July 23, 1982; 737-57-1129 NSC2, dated April 14, 1983; and 737-57-1129 NSC 3, dated May 18, 1995; is considered acceptable for compliance with the modification required by paragraph (b) of this AD.

Spares

(c) As of the effective date of this AD, no person shall install on any airplane any aluminum support fitting identified in the “Existing Part Number” column of Paragraph 2.D. of Boeing Service Bulletin 737-57-1129, Revision 2, dated May 28, 1998.

Alternative Methods of Compliance

(d) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Seattle ACO.

Note 3:

Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Seattle ACO.

Special Flight Permits

(e) Special flight permits may be issued in accordance with §§ 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

Issued in Renton, Washington, on March 9, 2000.

Donald L. Riggin,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.