RULES and REGULATIONS

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 90-NM-110-AD; Amendment 39-6801)

Airworthiness Directives; Boeing Model 747 Series Airplanes

Tuesday, November 6, 1990

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Final rule.

SUMMARY: This amendment supersedes an existing airworthiness directive (AD),

applicable to certain Boeing Model 747 series airplanes, which currently requires inspection of the 

fuselage skin lap splice between body station (BS) 340 and BS 400 at stringers (S)-6L and S-6R, and 

repair, if necessary. This action deletes the option of reinspecting known small cracks in lieu of 

repairing them before further flight, and reduces the repetitive inspection interval. This amendment is

prompted by further FAA consideration of the crack repair deferral option in the existing AD, and 

analysis results which indicate that a reduction of the inspection interval is warranted. This condition, 

if not corrected, could result in sudden loss of cabin pressurization and the inability of the fuselage to 

withstand failsafe loads.

EFFECTIVE DATE: December 11, 1990.

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.

FOR FURTHER INFORMATION CONTACT: Mr. Steven C. Fox, Seattle Aircraft Certification

Office, Airframe Branch, ANM-120Si telephone (206) 227-2777. Mailing address:

FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, 

Washington 98055-4056.

SUPPLEMENTARY INFORMATION: A proposal to amend part 39 of the Federal Aviation

Regulations by superseding AD 85-17-05, Amendment 39-5123 (50 FR 3335, August 19, 1985), 

applicable to Boeing Model 747 series airplanes, to require inspection of the fuselage skin lap splice 

between body station (BS) 340 and BS 400 at stringers S-6L and S-6R, and repair, if necessary, was 

published in the Federal Register on June 28, 1990 (55 FR 28219)
Interested persons have been afforded an opportunity to participate in the making of this amendment. 

Due consideration has been given to the comments received.

A foreign operator of Boeing Model 747 airplanes and the manufacturer commented

that the rule should be revised to reflect that flights with pressurization of 1.5

psi or below need not be counted as flight cycles and that a 1.2 adjustment factor

be used for the initial and repetitive inspections for Boeing Model 747SR airplanes

based on continued mixed operation at lower cabin pressure differentials. 

The FAA concurs and the final rule has been revised by adding two new paragraphs, C. and D'I to 

specify that flights with cabin pressure differentials of 1.5 psi or below need not be counted

as flight cycles, and that a 1.2 adjustment factor may be used for the initial and repetitive

inspections for Boeing Model 747SR airplanes based on continued mixed operation at

lower cabin pressure. (These factors have been included in similar AD's previously issued.)

One Air Transport Association (ATA) of America member operator requested that the

proposed initial inspection period be increased from 250 landings to 1,000 landings

so that this inspection could be accomplished at a scheduled C-check. The FAA

does not concur. The intent of this rule was to reduce the inspection interval

from 5,000 to 3,000 flight cycles, based on the 747 Aging Fleet Structures Working

Group's recommendation. The 250 landings initial inspection was based on allowing

the maximum credit (2,750 cycles) from the time the last previous inspection

required by AD 85-17-05 was accomplished.

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

described above. 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 603 Model 747 series airplanes of the affected design in the worldwide

fleet. It is estimated that 191 airplanes of U.S. registry would be affected by this AD, that it would take

approximately 8 manhours per airplane to accomplish the required actions, and that the average labor

cost would be $40 per manhour. Based on these figures, the total cost impact of the AD on U.S.

operators is estimated to be $61,120.

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 regulatory 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, 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.

§ 39.13 [Amended]

2. Section 39.13 is amended by superseding AD 85-17-05, Amendment 39-5123

(50 FR 3335, August 19, 1985), with the following new airworthiness directive:

Boeing: Applies to Model 747 series airplanes, identified in Boeing Service Bulletin 747-53-2253,

Revision 2, dated March 29, 1990, certificated in any category. Compliance required as indicated,

unless previously accomplished.

To prevent sudden loss of cabin pressurization and the inability to withstand fail-safe loads,

accomplish the following:

A. For airplanes that have not been modified in accordance with Boeing Service Bulletin 747-53-2253, 

Revision 2, dated March 29, 1990: In accordance with the schedule indicated below, perform a high

frequency eddy current inspection of the fuselage lap joint for cracks between body station (BS) 340

and BS 400, or aft as far as the crew door, at stringer (S)-6L and S-6R, in accordance with Boeing

Service Bulletin 747-53-2253, Revision 2, dated March 29, 1990.

1. Inspection schedule:

a. Unless previously accomplished within the last 2,750 landings, perform the initial inspection within 

the next 250 landings after the effective date of this AD, or prior to the accumulation of 10,000

landings, whichever occurs later.

b. Repeat the inspection thereafter at intervals not to exceed 3,000 landings.

2. If cracks are found, repair prior to further flight, in accordance with Boeing Service Bulletin

747-53-2253, Revision 2, dated March 29, 1990.
B. For airplanes that have been modified in accordance with Boeing Service Bulletin

747-53-2253, Revision 2, dated March 29, 1990: In accordance with the schedule below,

perform a high frequency eddy current inspection of the fuselage lap joint for cracks between as 340

and as 400, or aft as far as the crew door, at stringers (S)-6L and S-6R, in accordance with Boeing

Service Bulletin 747-53-2253, Revision 2, dated March 29, 1990.

1. Inspection schedule:

a. Unless previously accomplished within the last 2,750 landings, perform the initial inspection

within the next 250 landings after the effective date of this AD, or prior to the accumulation of

10,000 landings after the modification, whichever occurs later.

b. Repeat the inspection thereafter at intervals not to exceed 3,000 landings.

2. If cracks are found, repair prior to further flight, in accordance with Boeing Service Bulletin

747-53-2253, Revision 2, dated March 29, 1990.

C. For purposes of complying with this AD, the number of landings may be determined to be

equal to the number of pressurization cycles where the cabin pressure differential was greater

than 1.5 psi.

D. For Model 747SR airplanes only: Based on a continued mixed operation of lower cabin

differentials, the initial inspection thresholds and the repetitive inspection intervals specified

in this AD may be multiplied by a 1.2 adjustment factor.

E. An alternate means 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 submitted directly to the Manager, Seattle ACO, and a copy sent

to the cognizant FAA Principal Inspector (PI). The PI will then forward comments or 

concurrence to the Seattle ACO.

F. 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.

All persons affected by this directive who have not already received the appropriate service

documents from the manufacturer may obtain copies upon request to Boeing Commercial

Airplane Group, P.O. Box 3707, Seattle, Washington 98124. These documents may be examined

at the FAA, Northwest Mountain Region, Transport Airplane Directorate, 1601 Lind Avenue SW.,

Renton, Washington.

This amendment becomes effective December 11, 1990.

Issued in Renton, Washington, on October 25, 1990.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.

55 FR 46652-0