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RULES and REGULATIONS DEPARTMENT OF TRANSPORTATION Federal Aviation Administration 14 CFR Part 39 [Docket No. 91 -NM- 113 -AD; Amdt. 39 - 8068; AD 91 -22 -08] Airworthiness Directives; Boeing Model 727 Series Airplanes Friday, November 8, 1991 AGENCY: Federal Aviation Administration (FAA), DOT. ACTION: Final rule. SUMMARY: This amendment supersedes an existing airworthiness directive (AD), applicable to certain Boeing Model 727 series airplanes, which currently requires inspection for cracks and repair, if necessary, of the main landing gear (MLG) wheel we ll pressure floor. This action requires additional inspections of airplanes on which the terminating modification has been installed in accordance with the existing AD, requires inspections of additional airplanes on which the terminating mo dification was incorporated in production, requires an expanded inspection area for unmodified airplanes, reduces the initial inspection threshold, and limits the time that blind rivets may be used. This amendment is prom

pted by several reports of cracking in areas adjacent to the mo dification and in areas not required to be inspected by the existing AD. This condition, if not corrected, could result in loss of cabin pressure. DATES: Effective December 13, 1991. The incorporation by reference of certain publications listed in the regulations is approved by the Director of the Federal Register as of December 13, 1991. ADDRESSES: The applicable service information may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124. This information may be examined at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington; or at the Office of the Federal Register, 1100 L Street NW., room 8401, Washington, DC. FOR FURTHER INFORMATION CONTACT:Ms. Kathi N. Ishimaru, Seattle Aircraft Certification Office, Airframe Branch, ANM - 120S; telephone (20 6) 227 -2778. Mailing address: FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington 98055 -4056.2

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal Aviation Regulations by superseding AD 74 -21 -01, Amendment 39 - 1982 (39 FR 35332, October 1, 1974), applicable to Boeing Model 727 series airplanes, was published in the Federal Register on July 2, 1991 (56 FR 30351 ). That action proposed to require additional inspections of airplanes on which the terminating mo dification had been installed in accordance with the existing AD, to require inspections of additional airplanes on which the terminating modification was incorporated in production, to require an expanded inspection area for unmodified airplanes, to reduce the initial inspection threshold, and to limit the time that blind rivets may be used. 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 supported adoption of the proposed rule. Two commenters requested that the NPRM be withdrawn. They both reasoned that the size of the potential hole on previously modified airplanes is too small to be a safety of flight concern. They believe the cracks will be confined to the 10 -inch square unmodified area. The FAA does not concur. There have been two reports of cracks found after the mo dification straps were installed. It is reasonable to assume that the cracks were of undetecta ble size when the straps were installed and grew

to detectable sizes during subsequent pressurization cycles. The FAA has concluded that the straps will not limit the crack to the unmodified area. Consequently, an inspection of the unmodified area is necessary to find cracks before they extend into the modified area. Several commenters requested that the proposed inspection interval be increased from 2,000 flight cycles to the same intervals required by AD 90 - 17 -06, Amendment 39 - 6691 ( 55 FR 33099 , August 1 4, 1990). That AD requires repetitive inspections of the MLG wheel well pressure floor in the area fore and aft of the area described in the proposed rule. Repetitive inspections required by AD 90 - 17 -06 are at 4,000 flight cycle intervals for visual inspections, and at 5,000 flight cycle intervals for HFEC inspections. The commenters reasoned that, since the proposed rule and AD 90 - 17 -06 both specify inspection of similar structure, the inspection intervals should be the same. In addition, two commenters requested that the initial inspection threshold for airplanes with more than 12,000 flight cycles be increased from the proposed 2,000 flight cycles to 4,000 flight cycles so that the proposed visual inspections could be accomplished concurrently with those required by AD 90 - 17 -06. The FAA partially concurs with the requests. Paragraph (c) of the proposal refers to airplanes that have been modified with straps. The straps will not stop crack grow th, but they

wi ll inhibit the crack growth rate. The FAA has determined that the presence of the straps will permit an increase in the inspection interval and threshold without adversely affecting safety. Therefore, the airplanes identified in paragraph (c) of the proposed rule must be inspected visually or with dye p enetrant at intervals not to exceed 4,000 flight cycles, or inspected at 5,000 flight cycles intervals if a high frequency eddy current (HFEC) inspection is performed. In addition, the modified airplanes over the 12,000 flight cycle threshold must be inspected within 3,000 flight cycles, rather than the 2,000 flight cycles proposed in the Notice. Paragraphs (c) and (d) of the final rule have been modified to incorporate these changes. However, the FAA does not concur that the main landing gear wheel well pressure floor of an unmodified airplane has similar enough structure at all buttock lines and body stations to warrant identical inspection intervals and threshold at3

all locations. The area covered by AD 90 - 17 -06 has support structure more closely spaced than in the area covered by this AD action. The longer unsupported structure results in higher stresses in the pressure floor and potentially longer cracks. This justifies the shorter inspection interval required by this AD action. One commenter requested that, for the sake of clarity and convenience, the FAA should issue one AD to supersede both AD 90 - 17 -06 and AD 74 -21 -01. The FAA concurs that the request has merit since both AD's require inspection for cracks in the main landing gear wheel well pressure floor. However, the issuance of a new Notice and additional time for public comment would be required in order to combine the two AD's. The FAA has determined that it is not prudent to delay issuing this final rule. The FAA may consider combining the twoAD's in a future rulemaking action. One commenter requested that the proposed inspection requirements be added to the aging aircraft mo dification document so a separate AD would not be needed. The FAA does not concur. Incorporation of the request would delay the effective date of the proposed inspection requirements by approximately 12 months. To delay this action would be inappropriate, since the FAA has determined that an unsafe condition exists which has been documented by service experience. One commenter requested that the first sentence of proposed paragraph (c) be revised by inserting a comma after the word “subsequent,” so that it reads, “For airplanes with line number 1103 and subsequent, and earlier airplanes that have been mo dified * * *.” The commenter indicated that this revision will make it clear that the phrase “airplanes that have been mo dified” refers only to the “earlier” airplanes. The FAA concurs, since this was the intent of the paragraph's applicability. The final rule has been revised accordingly. One commenter requested that paragraph (f) of the Notice be clarified by adding reference to the “interim repair limits listed in Table V of the Accomplishment Instructions * * *” in lieu of merely the “limits listed in the Accomplishment Instructions * * *.” The FAA concurs and paragraph (f) of the final rule has been changed accordingly. Additionally, paragraph (e) also has been clarified by adding references to the interim repair limit to Table V. Since issuance of the proposed rule, Boeing Drawing, 65C36247, Revision New, has become available. This drawing specifies additional repair and modification procedures for addressing the subject cracking. Paragraph (h) of the final rule has been changed to add the new drawing as an additional optional method of terminating action for the repetitive inspections. Paragraphs (e) and (f) of the final rule also have been changed to add the new drawing as an optional repair method. After careful review o f 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 FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the rule. There are approximately 1,710 Model 727 series airplanes of the affected design in the worldwide fleet. It is estimated that 1,143 airplanes of U.S. registry will be affected by this AD, that it will take approximately 12 manhours per airplane to accomplish the required actions, and that the average labor cost will be $55 per manhour. Based on these figures, the total cost impact of the AD on U.S. operators is estimated to be $754,380 .4

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 p ower 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 “major rule” under Executive Order 12291 ; (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 im pact, positive or negative, on a substantial num ber of small entities under the criteria of the Regulatory Flexibility Act. A final evaluation has been prepared for this action and is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket. 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 14 CFR part 39 of the Federal Aviation Regulations as follows: PART 39

— [AMENDED]1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. 1354(a), 1421 and 1423; 49 U.S.C. 106(g) (Revised Pub. L. 97 -449, January 12, 1983); and 14 CFR 11.89 . 14 CFR § 39.13 § 39.13 [Amended] 14 CFR § 39.13 2. Section 39.13 is amended by removing Amendment 39 - 1982 and by adding with the fo llowing new airworthiness directive: 91 -22 -08. Boeing: Amendment 39 - 8068.Docket No. 91 -NM - 113 -AD.Supersedes AD 74 -21 -01, Amendment 39 - 1982. Applicability: Model 727 series airplanes, certificated in any category. Com pliance: Required as indicated, unless previously accomplished.5

To detect cracking in the main landing gear (MLG) wheel well pressure floor, accomplish the following: (a) For airplanes with line numbers 001 through 1102, except those modified in accordance with Boeing Alert Service Bulletin 727 - 53A0124, original release, dated May 3 , 1974; Revision 1, dated September 27, 1974; or Revision 2, dated May 2 , 1975: Prior to the compliance time specified in paragraph (a)(1) or (a)(2) of this AD, whichever occurs earlier, perform a detailed visual, high frequency eddy current (HFEC), or dye penetrant inspection for cracks in the pressure floor at body station (BS) 910, in accordance with Boeing Alert Service Bulletin 727 - 53A0124, Revision 3, dated November 30, 1989, or earlier FAA-approved revisions. (1) Prior to the accumulation of 15,000 landings or within 800 landings after November 2, 1974 (the effective date of AD 74 -21 -01, Amendment 39 - 1982), whichever occurs later; or (2) Prior to the accumulation of 1 2,000 landings or within 2,000 landings after the effective date of this AD, whichever occurs later. (b) For airplanes with line numbers 001 through 1102, except those modified in accordance with Boeing Alert Service Bulletin 727 - 53A0124, original release, dated May 3 , 1974; Revision 1, dated September 27, 1974; or Revision 2, dated May 2, 1975: Prior to the accumulation of 12,000 landings or within 2,000 landings after the effective date of this AD, whichever occurs later, perform a detailed visual, HFEC, or dye penetrant inspection for cracks in the pressure floor at BS 900 and BS 920, in accordance with Boeing Alert Service Bulletin 727 - 53A0124, Revision 3, dated November 30, 1989, or earlier FAA-approved revisions. (c) For airplanes with line number 1103 and subsequent, and earlier airplanes that have been modified in accordance with Boeing Alert Service Bulletin 727 - 53A0124, original release, dated May 3, 1974; Revision 1, dated Septem ber 27, 1974; or Revision 2, dated May 2, 1975: Prior to the accumulation of 12,000 landings since manufacture or within the next 3,000 landings after the effective date of this AD, whichever occurs later, perform a detailed visual, HFEC, or dye penetrant inspection to detect cracks in the pressure floor at BS 910, and BS 920 between buttock line (BL) 00 and right BL 10, in accordance with Boeing Alert Service Bulletin 727 - 53A0124, Revision 3, dated November 30, 1989. (d) The inspections required by paragraphs (a), (b), and (c) of this AD must be repeated in accordance with the fo llowing schedule: (1) Repeat the inspections required by paragraphs (a) or (b) of this AD at intervals not to exceed 2,000 landings. (2) Repeat the inspections required by paragraph (c) of this AD at intervals as follows: (i) If the immediately preceding inspection was performed using a visual or dye penetrant inspection technique, the next insp ection must be performed within 4,000 landings. (ii) If the immediately preceding inspection was performed using an HFEC inspection technique, the next inspection6

must be performed within 5,000 landings. (e) If cracks are detected that do not exceed the interim repair limits listed in Table V of the Accomplishment Instructions of Boeing Alert Service Bulletin 727 - 53A0124, Revision 3, dated November 30, 1989, prior to further flight, repair in accordance with the interim repair described in Part I of the Accom plishment Instructions, or the permanent repair described in Part II of the Accomplishment Instructions of that service bulletin, or repair in accordance with Boeing Drawing 65C36247, Revision New. The interim repair must be replaced, within 600 landings after accomplishment, with the permanent repair. (f) If cracks are found that exceed the interim repair limits listed in Table V of the Accomplishments Instructions of Boeing Alert Service Bulletin 727 - 53A0124, Revision 3, dated November 30, 1989, prior to further flight, accom plish the permanent repair described in Part II of the Accomplishment Instructions of that service bulletin, or repair in accordance with Boeing Drawing 65C36247, Revision New. (g) Blind fasteners installed in accordance with Part II of Boeing Alert Service Bulletin 727 - 53A0124, Revision 3, dated November 30, 1989, may be used as an interim repair only. The blind fasteners have a life limit of 10,000 landings before they must be replaced with solid fasteners in accordance with Part II of that service bulletin. The blind fasteners must be inspected for loose or mi ssing fasteners after accumulating 3,000 landings since installation or within 1,000 landings after the effective date of this AD, whichever occurs later, and thereafter must be inspected at intervals not to exceed 2,500 landings until replaced. Blind fasteners installed prior to the effective date of this AD must be replaced prior to the accumulation of 10,000 landings since installation or within 3,000 landings after the e ffective date of this AD, whichever occurs later. (h) Terminating action for the repetitive inspection requirements of this AD is as follows: (1) Incorporation of the preventative mo dification described in Part III or Part IV, as applicable, of the Accomplishment Instructions of B oeing Alert Service Bulletin 727 - 53A0124, Revision 3, dated November 30, 1989, constitutes terminating action for the repetitive inspection requirement of paragraph (d) of this AD. (2) Repair or mo dification in accordance with Boeing Drawing 65C36247, Revision New, constitutes terminating action for the repetitive inspection requirement of paragraph (d) of this AD. (3) Incorporation of the permanent repairs in accordance with paragraph (e) or (f) of this AD constitutes terminating action for the repetitive inspection requirement of paragraph (d) of this AD for the repaired area only. (i) An alternative method of compliance or adjustment of the compliance time, which provides an acceptable level of safety, may be used when approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA, Transport Airplane Directorate. Note: The request should be forwarded through an FAA Principal Maintenance Inspector, who may concur or c omment and then send it to the Manager, Seattle ACO.7

(j) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate airplanes to a base in order to comply with the requirements of this AD. (k) The inspection requirements shall be done in accordance with Boeing Service Bulletin 727 - 53A0124, Revision 3, dated November 30, 1989. The repair requirements shall be done in accordance with Boeing Service Bulletin 727 - 53A0124, Revision 3, dated Novem ber 30, 1989; or in accordance with Boeing Drawing 65C36247, draw n D ecem ber 13, 1990. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5U.S.C. 552(a) and 1 CFR Part 51. Copies may be obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington 98124. Copies may be inspected at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington, or at the Office of the Federal Register, 1100 L Street NW., room 8401, Washington, DC. This amendment supersedes Amendment 39 - 1982, AD 74 -21 -01. This amendment (39 - 8068, AD 91 -22 -08) becomes effective December 13, 1991. Issued in Renton, Washington, on October 9, 1991. Darrell M. Pederson, Acting Manager, Transport Airplane Directorate, Aircraft Certification Service. [FR Doc. 91 -27001 Filed 11 - 7 - 91; 8:45 am] BILLING CODE 4910 - 13 -M 56 FR 57233