Airworthiness Directives; Boeing Model 747 Series Airplanes

DEPARTMENT OF TRANSPORTATION

14 CFR Part 39

[Docket No. 93-NM-189-AD; Amendment 39-8946; AD 94-13-06]

Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule.

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SUMMARY: This amendment adopts a new airworthiness directive (AD),

applicable to certain Boeing Model 747 series airplanes, that requires

inspections to detect cracking in certain fuselage upper deck tension

ties, and repair or modification of any cracked tension ties. This

amendment is prompted by reports of fatigue cracking in tension ties.

The actions specified by this AD are intended to prevent failure of two

or more tension ties and the resultant rapid decompression of the

airplane.

DATES: Effective July 27, 1994.

The incorporation by reference of certain publications listed in

the regulations is approved by the Director of the Federal Register as

of July 27, 1994.

ADDRESSES: The service information referenced in this AD may be

obtained from Boeing Commercial Airplane Group, P.O. Box 3707, Seattle,

Washington 98124-2207. This information may be examined at the Federal

Aviation Administration (FAA), Transport Airplane Directorate, Rules

Docket, 1601 Lind Avenue, SW., Renton, Washington; or at the Office of

the Federal Register, 800 North Capitol Street, NW., suite 700,

Washington, DC.

FOR FURTHER INFORMATION CONTACT: Steven C. Fox, Aerospace Engineer,

Airframe Branch, ANM-120S, FAA, Transport Airplane Directorate, Seattle

Aircraft Certification Office, 1601 Lind Avenue, SW., Renton,

Washington 98055-4056; telephone (206) 227-2777; fax (206) 227-1181.

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

Aviation Regulations (14 CFR part 39) to include an airworthiness

directive (AD) that is applicable to certain Boeing Model 747 series

airplanes was published in the Federal Register on January 24, 1994 (59

FR 3527). That action proposed to require inspections to detect

cracking in certain fuselage upper deck tension ties, and repair or

modification of any cracked tension ties.

Interested persons have been afforded an opportunity to participate

in the making of this amendment. Due consideration has been given to

the comments received.

Two commenters support the proposed rule.

Several commenters request that the proposed 1,000-flight cycle

compliance time for low-time airplanes be revised to require that the

inspection be performed ``upon the accumulation of 20,000 total flight

cycles or within 1,000 flight cycles after the effective date of this

AD, whichever comes later.'' The FAA does not concur. Since cracking

has been found on airplanes that had accumulated less than 20,000

flight cycles, the FAA reasoned that requiring inspection of all

airplanes within 1,000 flight cycles, regardless of the total number of

flight cycles, would be prudent to preclude the propagation of cracks

in airplanes in the Model 747 fleet.

Two commenters request that the proposed rule be revised to include

a provision specifying that pressurization cycles of 2.0 psi or less

need not be counted as a flight cycle when determining the number of

flight cycles relative to the proposed compliance thresholds. The FAA

does not concur. The FAA finds that operating at cabin pressure

differentials of 2.0 psi or less is applicable to only one operator.

The FAA does not consider it appropriate to include various provisions

in an AD applicable to a single operator's unique use of an affected

airplane. Further, this commenter does not compile data for each of its

airplanes so that an individual airplane's pressurization cycles could

be determined; instead, it uses a fleet average to calculate the

equivalent number of pressurization cycles. The FAA does not consider

it appropriate to use approximations for determining compliance with

this AD. Furthermore, since there are numerous factors that affect the

calculation of flight cycles, such as total number of low pressure

cycles, amount of thrust, number of gross weight flight cycles, etc.,

the FAA has determined that these mitigating factors could be best

evaluated through requests for alternative methods of compliance, as

provided for in paragraph (c) of the final rule.

One commenter requests that the FAA and Boeing review the

requirement for inspections contained in AD 93-06-01, amendment 39-8526

(58 FR 19571, April 15, 1993), which requires that the FAA-approved

maintenance inspection program include inspections that will give no

less than the required damage tolerance rating (DTR) for each

Structural Significant Item (SSI). This commenter states that the

proposed inspection of the tension ties may be included in the

requirement for inspections contained in AD 93-06-01. The FAA concurs

and has reviewed the requirement for inspections contained in AD 93-06-

01. This AD was prompted by reports of fatigue cracks that were

detected while performing inspections specified by the Supplemental

Structural Inspection Document (SSID) program, which was required to be

implemented by AD 93-06-01. The purpose of that AD is to implement an

inspection program of a sample number of airplanes, which will detect

the potential for cracking in specific areas of the airplane that are

critical for safety of flight. Whenever cracks are found in an SSI

during an inspection in accordance with the SSID program, the FAA takes

rulemaking action to correct these findings of an unsafe condition

within the applicable fleet. This AD is issued in response to such a

finding. Therefore, the FAA will, in a separate rulemaking action,

revise AD 93-06-01 to remove the requirement to inspect the tension

ties.

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 as proposed.

There are approximately 203 Model 747 series airplanes of the

affected design in the worldwide fleet. The FAA estimates that 113

airplanes of U.S. registry will be affected by this AD, that it will

take approximately 5 work hours per airplane to accomplish the required

actions, and that the average labor rate is $55 per work hour. Based on

these figures, the total cost impact of the AD on U.S. operators is

estimated to be $31,075, or $275 per airplane.

The total cost impact figure discussed above is based on

assumptions that no operator has yet accomplished any of the

requirements of this AD action, and that no operator would accomplish

those actions in the future if this AD were not adopted.

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 ``significant regulatory action'' under Executive Order 12866;

(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 it is contained in the Rules Docket. A copy of it may be obtained

from the Rules Docket at the location provided under the caption

ADDRESSES.

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 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. App. 1354(a), 1421 and 1423; 49 U.S.C.

106(g); and 14 CFR 11.89.

Sec. 39.13 [Amended]

2. Section 39.13 is amended by adding the following new

airworthiness directive:

94-13-06 Boeing: Amendment 39-8946. Docket 93-NM-189-AD.

Applicability: Model 747 series airplanes, as listed in Boeing

Service Bulletin 747-53-2371, dated July 29, 1993; certificated in

any category.

Compliance: Required as indicated, unless accomplished

previously.

To prevent rapid decompression of the airplane due to failure of

two or more tension ties, accomplish the following:

(a) Prior to the accumulation of 1,000 flight cycles after the

effective date of this AD, unless accomplished previously within the

last 2,000 flight cycles, perform a detailed visual inspection to

detect cracking of the outboard end tension ties, in accordance with

Boeing Service Bulletin 747-53-2371, dated July 29, 1993.

(1) If no cracking is detected, repeat the inspection thereafter

at intervals not to exceed 3,000 flight cycles until the repair or

modification required by paragraph (a)(2) of this AD is

accomplished.

(2) If any cracking is detected, prior to further flight, repair

or modify the cracked tension tie in accordance with the service

bulletin. Accomplishment of this repair or modification terminates

the repetitive inspection requirement of paragraph (a) of this AD.

Note 1: Although AD 84-19-01, amendment 39-4913, requires

inspections of the tension ties at body station (BS) 760 on a

certain group of Model 747 series airplanes, and at BS 780 on

certain other Model 747 series airplanes, the inspections required

by this AD do not retract the inspection requirements of that AD.

(b) Prior to the accumulation of 10,000 flight cycles following

repair or modification of any tension tie in accordance with

paragraph (a)(2) of this AD, perform a detailed visual inspection to

detect cracking of the repaired or modified outboard end tension tie

in accordance with Boeing Service Bulletin 747-53-2371, dated July

29, 1993.

(1) If no cracking is detected, repeat this inspection

thereafter at intervals not to exceed 6,000 flight cycles.

(2) If any cracking is detected, prior to further flight, repair

or modify in accordance with the service bulletin, and repeat the

inspection required by paragraph (b) of this AD.

(c) 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 2: Information concerning the existence of approved

alternative methods of compliance with this AD, if any, may be

obtained from the Seattle ACO.

(d) Special flight permits may be issued in accordance with

sections 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.

(e) The inspections, repair, and modification shall be done in

accordance with Boeing Service Bulletin 747-53-2371, including the

``ADDENDUM,'' dated July 29, 1993. This incorporation by reference

was approved by the Director of the Federal Register in accordance

with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from

Boeing Commercial Airplane Group, P.O. Box 3707, Seattle, Washington

98124-2207. Copies may be inspected at the FAA, Transport Airplane

Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the

Office of the Federal Register, 800 North Capitol Street, NW., suite

700, Washington, DC.

(f) This amendment becomes effective on July 27, 1994.

Issued in Renton, Washington, on June 14, 1994.

Robert C. McCracken,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-14903 Filed 6-24-94; 8:45 am]

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