Airworthiness Directives; Boeing Model 747 Series Airplanes

DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 93-NM-164-AD; Amendment 39-8902; AD 94-09-13]

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

replacement of certain pneumatic duct couplings with redesigned

couplings. This amendment is prompted by reports of failures of certain

duct couplings installed on the wing leading edge pneumatic duct. The

actions specified by this AD are intended to prevent such failures,

which could lead to structural damage to the wing leading edge, flight

control problems, or fire.

DATES: Effective June 17, 1994.

The incorporation by reference of certain publications listed in

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

of June 17, 1994.

ADDRESSES: The service information referenced in this AD may be

obtained from PTI Technologies, Inc., 950 Rancho Conejo Boulevard,

Newbury Park, California 91320. 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: Barbara Mudrovich, Aerospace Engineer,

Systems and Equipment Branch, ANM-130S, FAA, Transport Airplane

Directorate, Seattle Aircraft Certification Office, 1601 Lind Avenue,

SW., Renton, Washington 98055-4056; telephone (206) 227-2670; fax (206)

227-1181.

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

Aviation Regulations to include an airworthiness directive (AD) that is

applicable to certain Boeing Model 747 series airplanes was published

in the Federal Register on December 9, 1993 (58 FR 64707). That action

proposed to require replacement of certain pneumatic duct couplings

installed on the wing leading edge pneumatic duct.

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 proposal.

One commenter requests that the proposal be revised to permit

operators to perform repetitive dye penetrant inspections to detect

fatigue cracking of the duct couplings at intervals of 15 months, in

lieu of the proposed mandatory replacement of the couplings at 15

months. This commenter states that it has found only one failure of a

duct coupling, but the failed coupling was at a location different from

that addressed by the proposal. Additionally, the commenter found

excess misalignment of the pneumatic ducts at the location of the

failed duct, and considers that this situation contributed to the

coupling failure. The commenter has already performed a dye penetrant

inspection of the wing leading edge pneumatic duct couplings on its

fleet of affected airplanes, but has found no fatigue cracking. The FAA

does not concur with the commenter's request for several reasons.

First, dye penetrant inspections have not been shown to be a reliable

method for detecting cracks in the couplings. Second, the couplings in

the vicinity of the struts (addressed by this AD action) are of highest

concern, because of the increased risk of damage in that area, should a

duct burst. Third, the misalignment referred to by the commenter has

been found to be associated with maintenance activity; this problem has

been addressed with improved installation instructions that have been

added recently to the Model 747 Maintenance Manual. While misalignment

has been shown to be a contributing factor in the coupling failures,

fatigue cracking is the main concern. The new design couplings that

were installed on airplanes beginning at line number 220, and that are

required to be installed in accordance with this AD, have not exhibited

any fatigue or other failures. In light of these items, the FAA has

determined that installation of the new design couplings is both

appropriate and warranted.

Another commenter requests that the proposal be revised to include

the option of performing an aided visual inspection of the subject

couplings within 15 months and replacement of the couplings within 24

months. The FAA does not concur. The FAA does not consider a visual

inspection to be adequate for detecting critical cracks in the

couplings, even as an interim measure. The FAA has determined that

replacement of the couplings with the new design couplings is the only

method to effectively address the unsafe condition presented by failure

of the subject couplings.

One commenter requests that the proposed compliance time of 15

months be extended to 18 months in order to allow the replacement to be

accomplished during the time of this commenter's regularly scheduled

``C'' check. The commenter states that the adoption of the proposed

compliance time of 15 months would require that special times be

scheduled for the accomplishment of this replacement, at additional

expense. The FAA does not concur. The proposed compliance time was

selected based on the average ``C'' check interval for the majority of

affected operators. It was also selected based on the degree of urgency

associated with addressing the subject unsafe condition, the

availability of required parts, and the practical aspect of replacing

the required parts within a maximum interval of time allowable for all

affected airplanes to continue to operate without compromising safety.

In light of these items, the FAA has determined that 15 months for

compliance is appropriate. However, paragraph (b) of the final rule

does provide affected operators the opportunity to apply for an

adjustment of the compliance time if sufficient data are presented to

justify such an adjustment.

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 219 Model 747 series airplanes of the

affected design in the worldwide fleet. The FAA estimates that 132

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

take approximately 12 work hours per airplane to accomplish the

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

Required parts will cost approximately $8,486 per airplane. Based on

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

estimated to be $1,207,272, or $9,146 per airplane.

The number of required work hours for the replacement of the duct

couplings, as indicated above, is presented as if the accomplishment of

that action was to be conducted as a ``stand alone'' action. However,

the 15-month compliance time specified in paragraph (a) of this AD

should allow ample time for the duct coupling replacement to be

accomplished coincidentally with scheduled major airplane inspection

and maintenance activities, thereby minimizing the costs associated

with special airplane scheduling.

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 FAA recognizes that the obligation to maintain aircraft in an

airworthy condition is vital, but sometimes expensive. Because AD's

require specific actions to address specific unsafe conditions, they

appear to impose costs that would not otherwise be borne by operators.

However, because of the general obligation of operators to maintain

aircraft in an airworthy condition, this appearance is deceptive.

Attributing those costs solely to the issuance of this AD is

unrealistic because, in the interest of maintaining safe aircraft, most

prudent operators would accomplish the required actions even if they

were not required to do so by the AD.

A full cost-benefit analysis has not been accomplished for this AD.

As a matter of law, in order to be airworthy, an aircraft must conform

to its type design and be in a condition for safe operation. The type

design is approved only after the FAA makes a determination that it

complies with all applicable airworthiness requirements. In adopting

and maintaining those requirements, the FAA has already made the

determination that they establish a level of safety that is cost-

beneficial. When the FAA, as in this AD, makes a finding of an unsafe

condition, this means that this cost-beneficial level of safety is no

longer being achieved and that the required actions are necessary to

restore that level of safety. Because this level of safety has already

been determined to be cost-beneficial, a full cost-benefit analysis for

this AD would be redundant and unnecessary.

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 14 CFR part

39 of the Federal Aviation Regulations 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:

94-09-13 Boeing: Amendment 39-8902. Docket 93-NM-164-AD.

Applicability: Model 747 series airplanes, line position 1

through 219 inclusive; certificated in any category.

Compliance: Required as indicated, unless accomplished

previously.

To prevent failure of duct couplings installed on the wing

leading edge pneumatic duct installed in the vicinity of the strut,

which could lead to structural damage to the wing leading edge,

flight control problems, or fire, accomplish the following:

(a) Within 15 months after the effective date of this AD,

replace duct couplings having part number (P/N) 7540600 and 7540602,

with duct couplings having P/N 7541749 and 7541751, in accordance

with Purolator Service Bulletin FSC-912, dated December 1972, at the

following locations:

(1) The coupling that connects the tee duct at the inboard

struts to the pneumatic ducting of the engine in the struts;

(2) The coupling that connects the tee duct at the inboard

struts to the pneumatic ducting of the wing leading edge outboard of

the inboard struts; and

(3) The coupling that connects the pneumatic ducting of the wing

leading edge to the pneumatic ducting of the engine in the outboard

struts.

(b) 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: Information concerning the existence of approved

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

obtained from the Seattle ACO.

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

Federal Aviation Regulations (FAR) 21.197 and 21.199 to operate the

airplane to a location where the requirements of this AD can be

accomplished.

(d) The replacement shall be done in accordance with Purolator

Service Bulletin FSC-912, dated December 1972. 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 PTI Technologies, Inc., 950 Rancho Conejo Boulevard,

Newbury Park, California 91320. 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.

(e) This amendment becomes effective on June 17, 1994.

Issued in Renton, Washington, on April 21, 1994.

Darrell M. Pederson,

Acting Manager, Transport Airplane Directorate, Aircraft Certification

Service.

[FR Doc. 94-10115 Filed 5-17-94; 8:45 am]

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