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Proposed Rule

Airworthiness Directives; Boeing Model 747 Series Airplanes

Document Details

Information about this document as published in the Federal Register.

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Start Preamble

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 747 series airplanes. That AD currently requires inspections to detect fatigue cracking of the vertical beam webs and chords of the nose wheel well (NWW) and of the inner chord and web of the fuselage frames at body station (BS) 300 and BS 320, and repair, if necessary. This action would expand the applicability of the existing AD to include additional airplanes, and add new requirements for repetitive inspections to detect fatigue cracking of the NWW vertical beam webs and frames from BS 260 to BS 320, and follow-on actions, if necessary, which would end the currently required inspections for airplanes subject to them. This action also provides terminating action for the new repetitive inspections. The actions specified by the proposed AD are intended to detect and correct fatigue cracking of the NWW vertical beam webs and frames, which could result in collapse of the NWW pressure bulkhead and subsequent rapid decompression of the airplane.

DATES:

Comments must be received by April 30, 2001.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 2000-NM-276-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. Comments may be submitted via fax to (425) 227-1232. Comments may also be sent via the Internet using the following address: 9-anm-nprmcomment@faa.gov. Comments sent via fax or the Internet must contain “Docket No. 2000-NM-276-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 for Windows or ASCII text.

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.

Start Further Info

FOR FURTHER INFORMATION CONTACT:

Rick Kawaguchi, Aerospace Engineer, Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98055-4056; telephone (425) 227-1153; fax (425) 227-1181.

End Further Info End Preamble Start Supplemental Information

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 action may be changed in light of the comments received.

Submit comments using the following format:

  • Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
  • For each issue, state what specific change to the proposed AD is being requested.
  • Include justification (e.g., reasons or data) for each request.

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 action must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 2000-NM-276-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. 2000-NM-276-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

On December 20, 1996, the FAA issued AD 96-26-04, amendment 39-9867 (61 FR 69026, December 31, 1996), applicable to certain Boeing Model 747 series airplanes, to require a one-time inspection to detect fatigue cracking of the vertical beam webs and chords of the nose wheel well (NWW) at body station (BS) 300 and BS 320, repetitive inspections to detect fatigue cracking of the inner chord and web of the fuselage frames at BS 300 and BS 320, and repair, if necessary. That action was prompted by a report indicating that the fuselage frames at BS 300 and BS 320 severed approximately 10 inches outboard of the NWW side panel and resulted in accelerated fatigue cracking Start Printed Page 14868and subsequent failure of the adjacent NWW vertical beams. The requirements of that AD are intended to detect and correct such fatigue cracking, which could result in collapse of the NWW pressure bulkhead and subsequent rapid decompression of the airplane.

Actions Since Issuance of Previous Rule

Since the issuance of that AD, the FAA has received several reports of cracking in the NWW vertical beam webs and frames. On one airplane, a severed frame and vertical beam were found at BS 320 on the right-hand side of the airplane. Additional cracking was found on the vertical beams at BS 300 and BS 320 on the left-hand side of the airplane. This airplane had accumulated 17,743 flight cycles.

On another airplane, which had accumulated 17,329 flight cycles, cracks were found in the vertical beams at BS 300 and BS 320 on the left and right sides of the airplane, as well as in the top panel intercostal in the nose wheel well between BS 280 and BS 300.

Based on these reports of cracking, the FAA has determined that the detailed visual inspections required by the existing AD are not adequate to detect fatigue cracking. Also, cracking may exist outside the areas required to be inspected per the existing AD. In addition, airplanes modified to have improved frames, per Boeing Service Bulletin 747-53-2272, were excluded from the applicability of the existing AD. The FAA finds that, though these airplanes have improved frames, they still have the same vertical beams that are susceptible to fatigue cracking. For these reasons, the FAA finds that it is necessary to require additional inspections on airplanes affected by the existing AD and to expand the applicability of the existing AD to include airplanes with improved frames.

Explanation of Relevant Service Information

The FAA has reviewed and approved Boeing Alert Service Bulletin 747-53A2293, Revision 8, dated July 13, 2000. Among other things, this service bulletin describes new procedures for repetitive inspections to detect fatigue cracking of NWW vertical beam webs and frames from BS 260 to BS 320 (defined in the service bulletin as “Area 4”), and follow-on actions, if necessary. Inspection procedures include:

  • Open-hole high frequency eddy current (HFEC) inspections to detect fatigue cracking of the BS 300 and BS 320 frame inner chords inboard of stringer 39,
  • Surface HFEC inspections at all fastener locations common to the inner and outer chords of the NWW vertical beams, and
  • Open-hole HFEC inspection of tool holes and insulation blanket standoff holes in the vertical beams.

If any cracking is found, follow-on actions include secondary internal and external detailed visual inspections or an HFEC inspection of adjacent areas to detect any additional cracking, and repair or installation of a modification that involves replacing vertical beam webs and frames, as applicable, with new parts. This modification eliminates the need for the repetitive inspections described previously, and may also be done, but is not required, on airplanes with no cracking.

Accomplishment of the actions specified in the service bulletin is intended to adequately address the identified unsafe condition.

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 96-26-04 to continue to require, for currently affected airplanes, inspections to detect fatigue cracking of the vertical beam webs and chords of the nose wheel well (NWW) and of the inner chord and web of the fuselage frames at body station (BS) 300 and BS 320, and repair, if necessary. The proposed AD would add new requirements for repetitive inspections to detect fatigue cracking of NWW vertical beam webs and frames from BS 260 to BS 320, and follow-on actions, if necessary, which would end the currently required inspections for affected airplanes. The proposed AD also would provide an optional terminating action for the repetitive inspections. The actions would be required to be accomplished in accordance with the service bulletin described previously, except as discussed below in the section titled, “Differences Between Service Bulletin and This Proposed AD.”

Operators also should note that paragraph (f) of this proposed AD applies to airplanes in Groups 1 through 11 on which cracking was detected during the inspection required by paragraph (a) of the existing AD. Though the FAA intended that all airplanes subject to the existing AD must repeat the paragraph (a) inspection at regular intervals, the FAA has determined that airplanes on which cracking was repaired per paragraph (a)(2) may not have been repetitively inspected. Therefore, paragraph (f) of this proposed AD would require that affected airplanes not inspected per paragraph (a) within the last 100 flight cycles be inspected per paragraph (c) of this AD within 100 flight cycles after the effective date of this AD. The FAA has determined that such a compliance time is necessary to ensure continued safety of flight for these airplanes.

Interim Action

This is considered to be interim action. The FAA is currently considering requiring the replacement of vertical beam webs and frames, as applicable, with new parts, which is provided in this AD as a required corrective action (for airplanes with cracking) or an optional terminating action (for airplanes without cracking). If the FAA decides to mandate such replacement, we will invite public comment at that time.

Differences Between Service Bulletin and This Proposed AD

Procedure 1, as specified in the service bulletin, applies to (among other airplanes) certain airplanes in Groups 1 through 11 that are already subject to the inspections required by AD 96-26-04. For airplanes subject to Procedure 1, the service bulletin specifies a compliance time of the latest of 10,000 total flight cycles, 100 flight cycles after the last inspection per AD 96-26-04, or, for airplanes not yet inspected per AD 96-26-04, within 50 flight cycles after January 6, 1997 (the effective date of AD 96-26-04). The FAA finds that this compliance time could be confusing for operators. Therefore, this proposed AD specifies a simpler compliance time of 10,000 total flight cycles or 100 flight cycles after the last inspection per paragraphs (a)(1) of this AD for the subject airplanes. Also, paragraph (e) of the proposed AD provides for airplanes subject to Procedure 1 that have not been inspected per the existing AD. That paragraph allows operators of affected airplanes to do paragraph (c) of this AD instead of paragraphs (a) and (b) of this AD, provided that the inspections are done at the compliance times provided in paragraphs (a) and (b).

In addition, Procedure 2, as specified in the service bulletin, applies to airplanes in Groups 1 through 11 on which frame replacement per Boeing Service Bulletin 747-53-2272 has been done, as well as airplanes in Groups 12 and 13. For airplanes subject to Procedure 2, the service bulletin specifies a compliance time of 10,000 total flight cycles or 1,500 flight cycles after January 6, 1997 (the effective date Start Printed Page 14869of the existing AD). The FAA finds that, because the airplanes subject to Procedure 2 were not included in the applicability of the existing AD, adopting the compliance time specified in the service bulletin could result in some airplanes being out of compliance with this proposed AD as of the effective date of this AD. The FAA finds that, while it is necessary for the affected airplanes to be inspected in a timely manner, it would be inappropriate to ground these airplanes until the required inspection can be done. Therefore, for airplanes subject to Procedure 2, this proposed AD includes a grace period of 100 flight cycles after the effective date of this AD.

Cost Impact

There are approximately 562 airplanes of the affected design in the worldwide fleet. The FAA estimates that 179 airplanes of U.S. registry would be affected by this proposed AD.

For affected airplanes, the inspections that are currently required by AD 96-26-04 take approximately 24 work hours per airplane, at an average labor rate of $60 per work hour. Based on these figures, the FAA estimates the cost impact of the currently required actions to be $1,440 per affected airplane, per inspection cycle.

The new inspections that are proposed in this AD action would take approximately 4 work hours per airplane to accomplish, at an average labor rate of $60 per work hour. Based on these figures, the FAA estimates the cost impact of these new actions on U.S. operators to be $42,960, or $240 per airplane, per inspection cycle.

The cost impact figures discussed above are based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this proposed AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions.

Regulatory Impact

The regulations proposed herein 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. Therefore, it is determined that this proposal would not have federalism implications under Executive Order 13132.

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.

Start List of Subjects

List of Subjects in 14 CFR Part 39

End List of Subjects

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:

Start Part

PART 39—AIRWORTHINESS DIRECTIVES

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

Start Authority

Authority: 49 U.S.C. 106(g), 40113, 44701.

End Authority
[Amended]

2. Section 39.13 is amended by removing amendment 39-9867 (61 FR 69026, December 31, 1996), and by adding a new airworthiness directive (AD), to read as follows:

Boeing: Docket 2000-NM-276-AD. Supersedes AD 96-26-04, Amendment 39-9867.

Applicability: Model 747 series airplanes, line numbers 1 through 685 inclusive, certificated in any category; except as excluded in the table below.

Airplanes Excluded from Applicability of this AD

Airplane Group (as listed in Boeing Alert Service Bulletin 747-53A2293, Revision 8, dated July 13, 2000)Area 4 modified per Boeing Service Bulletin (BSB) 747-53-2293?Zone 1 modified per BSB 747-53-2272?Excepted from this AD?
1-11YesYesYes.
1-11NoYesNo.
1-11YesNoNo.
12-13YesN/AYes.
12-13NoN/ANo.

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 (i)(1) 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 detect and correct fatigue cracking of nose wheel well (NWW) vertical beams and frames, which could result in collapse of the NWW pressure bulkhead and subsequent rapid decompression of the airplane, accomplish the following:

Restatement of Requirements of AD 96-26-04

Repetitive Inspections of Frame Inner Chord and Web and Repair

(a) For airplanes with line numbers 1 through 678 inclusive on which the Section 41 frame replacement in zone 1 specified in Boeing Service Bulletin 747-53-2272 has not been accomplished: Prior to the accumulation of 10,000 total flight cycles, or within 50 flight cycles after January 6, 1997 (the effective date of AD 96-26-04, amendment 39-9867), whichever occurs later, perform a detailed visual inspection to detect fatigue cracking of the inner chord and Start Printed Page 14870web of the left side and right side of body station (BS) 300 and BS 320 fuselage frames from the NWW side panel outboard to stringer 39, in accordance with normal maintenance practices. Pay particular attention to the area where the NWW vertical beam inner chord interfaces with the fuselage frame.

(1) If no cracking is detected, repeat the detailed visual inspection thereafter at intervals not to exceed 100 flight cycles, until paragraph (c) of this AD is done.

(2) If any cracking is detected, prior to further flight, repair in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the Manager's approval letter must specifically reference this AD.

One-Time Inspection of Vertical Beam Webs and Chords and Repair

(b) For airplanes with line numbers 1 through 678 inclusive on which the Section 41 frame replacement in zone 1 specified in Boeing Service Bulletin 747-53-2272 has not been accomplished: Prior to the accumulation of 10,000 total flight cycles, or within 50 flight cycles after January 6, 1997, whichever occurs later, perform a one-time detailed visual inspection to detect fatigue cracking of the left and right side vertical beam webs and chords of the NWW at BS 300 and BS 320, in accordance with normal maintenance procedures.

(1) If no cracking is detected, no further action is required by this paragraph.

(2) If any cracking is detected, prior to further flight, repair in accordance with a method approved by the Manager, Seattle ACO. For a repair method to be approved by the Manager, Seattle ACO, as required by this paragraph, the Manager's approval letter must specifically reference this AD.

New Requirements of This AD

Note 2:

For the purposes of this AD, a detailed visual inspection is defined as: “An intensive visual examination of a specific structural area, system, installation, or assembly to detect damage, failure, or irregularity. Available lighting is normally supplemented with a direct source of good lighting at intensity deemed appropriate by the inspector. Inspection aids such as mirror, magnifying lenses, etc., may be used. Surface cleaning and elaborate access procedures may be required.”

Repetitive Inspections

(c) Do inspections to detect fatigue cracking of NWW vertical beam webs and frames, as applicable, from BS 260 to BS 320 (“Area 4”), per the applicable procedure shown in Table 1 of this AD and the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2293, Revision 8, dated July 13, 2000. For affected airplanes, inspection per this paragraph ends the repetitive inspections required by paragraph (a). Table 1 follows:

Table 1—Determining the Applicable Procedure

Airplane GroupArea 4 inspected per the original issue or Revisions 1 through 7 of BSB 747-53-2293?Area 4 modified per BSB 747-53-2293?Zone 1 modified per BSB 747-53-2272?Applicable procedure and figures in service bulletin
1-11NoNoNoProcedure 1; Figures 4 and 19, and Figure 10, as applicable.
1-11NoNoYesProcedure 2; Figures 11 and 12.
1-11YesNoNoProcedure 3; Figures 4 and 13, and Figures 10 and 14, as applicable.
1-11YesNoYesProcedure 4; Figures 11 and 15.
1-11NoYesNoProcedure 5; Figures 10, 16, and 17, as applicable.
1-11YesYesNoProcedure 6; Figure 18; and Figure 10, 14 or 17, as applicable.
12-13NoNoN/AProcedure 2; Figures 11 and 12.
12-13YesNoN/AProcedure 4; Figures 11 and 15.

Repetitive Inspections: Compliance Schedule

(d) For all airplanes, do the inspection in paragraph (c) of this AD per the schedule in Table 2 or Table 3 of this AD, as applicable, except as provided by paragraph (f) of this AD. Thereafter, repeat the inspection at the interval specified in Table 2 or Table 3 of this AD, as applicable, until paragraph (h) of this AD is done. Tables 2 and 3 follow:

Table 2.—Compliance Schedule—Procedures 1, 2, and 5

For airplanes subject toDo the initial inspection before the latest ofRepeat the inspection in the service bulletin as follows:
If most recent inspection was per Option 1, repeat at least everyIf most recent inspection was per Option 2, repeat at least every
Procedure 110,000 total flight cycles or 100 flight cycles after the last inspection per paragraph (a) of this AD1,500 flight cycles100 flight cycles.
Procedure 210,000 total flight cycles or 1,500 flight cycles after January 6, 1997 or 100 flight cycles after the effective date of this AD1,500 flight cycles500 flight cycles.
Start Printed Page 14871
Procedure 510,000 total flight cycles or 500 flight cycles since modification of Area 4 in accordance with BSB 747-53-2293 or 100 flight cycles after the effective date of this AD1,500 flight cycles100 flight cycles.

Table 3.—Compliance Schedule—Procedures 3, 4, and 6

For airplanes subject toDo the initial inspection as follows, as applicable:Repeat the inspection in the service bulletin as follows:
If most recent inspection was per Option 1, do the inspection:If most recent inspection was per Option 2, do the inspection:If most recent inspection was per Option 1, repeat at least everyIf most recent inspection was per Option 2, repeat at least every
Procedure 3Within 500 flight cycles since last inspectionWithin 100 flight cycles since last inspection1,500 flight cycles100 flight cycles.
Procedure 4Within 500 flight cycles since last inspectionWithin 100 flight cycles since last inspection1,500 flight cycles500 flight cycles.
Procedure 6Within 500 flight cycles since last inspectionWithin 100 flight cycles since last inspection1,500 flight cycles100 flight cycles.

Exceptions to Inspections per Paragraphs (a) and (b)

(e) For airplanes subject to paragraphs (a) and (b) of this AD: Airplanes inspected per paragraph (c) of this AD within the compliance time specified in paragraphs (a) and (b) of this AD are not required to be inspected per paragraphs (a) and (b) of this AD.

(f) For airplanes in Groups 1 through 11 on which cracking was repaired prior to the effective date of this AD per paragraph (a)(2) of this AD: If an inspection per paragraph (a) has not been done within the last 100 flight cycles before the effective date of this AD, do the inspection in paragraph (c) of this AD within 100 flight cycles after the effective date of this AD.

Corrective Actions

(g) If any cracking is found during any inspection required by paragraph (c) or (d) of this AD, prior to further flight, perform corrective actions, including secondary inspections to detect further cracking, in accordance with the applicable procedure in the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2293, Revision 8, dated July 13, 2000.

Optional Terminating Action

(h) Replacement of vertical beams and frames, as applicable, in accordance with the applicable procedure in the Accomplishment Instructions of Boeing Alert Service Bulletin 747-53A2293, Revision 8, dated July 13, 2000, ends the requirements of this AD.

Alternative Methods of Compliance

(i)(1) 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 ACO. 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.

(2) Alternative methods of compliance, approved previously in accordance with AD 96-26-04, amendment 39-9867, are approved as alternative methods of compliance with paragraphs (a) and (b) of this AD.

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

(j) 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.

Start Signature

Issued in Renton, Washington, on March 7, 2001.

Vi L. Lipski,

Manager, Transport Airplane Directorate, Aircraft Certification Service.

End Signature End Part End Supplemental Information

[FR Doc. 01-6286 Filed 3-13-01; 8:45 am]

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