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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 well 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 modification 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 prompted by several reports of cracking in areas adjacent to the modification 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 (206) 227-2778. Mailing address: FAA, Northwest Mountain Region, Transport 

Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington 98055-4056.
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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 modification 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 

modification straps were installed. It is reasonable to assume that the cracks were of undetectable 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 14, 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 growth, but they will 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 penetrant 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 at 
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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 two AD's in a future rulemaking action.

One commenter requested that the proposed inspection requirements be added to the aging aircraft modification 

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 modified * * *.” The commenter indicated that this revision will make it clear that the phrase “airplanes that 

have been modified” 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 of 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.
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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 power 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 impact, positive or negative, on a substantial number 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 following 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.

Compliance: Required as indicated, unless previously accomplished.
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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 12,000 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 September 

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 following 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 inspection must be performed within 4,000 landings.

(ii) If the immediately preceding inspection was performed using an HFEC inspection technique, the next inspection 
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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 Accomplishment 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, accomplish 

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 missing 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 

effective 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 modification described in Part III or Part IV, as applicable, of the Accomplishment Instructions of Boeing 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 modification 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 comment and then send it to the Manager, Seattle ACO.
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(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 November 30, 1989; or in accordance with Boeing Drawing 65C36247, drawn December 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