[Federal Register Volume 66, Number 27 (Thursday, February 8, 2001)]
[Notices]
[Pages 9621-9622]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 01-3309]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration


Advisory Circular 120-73, Damage Tolerance Assessment of Repairs 
to Pressurized Fuselages

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of issuance of advisory circular.

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SUMMARY: This notice announces the issuance of Advisory Circular (AC) 
120-73, ``Damage Tolerance Assessment of Repairs to Pressurized 
Fuselages.'' The AC provides guidance on acceptable means of 
incorporating FAA-approved repair assessment guidelines in air carrier 
maintenance or inspection programs.

DATES: Advisory Circular 120-73 was issued on December 14, 2000, by the 
Director of the Aircraft Certification Service, Federal Aviation 
Administration.
    How to Obtain Copies: You can get a paper copy of AC 120-73 by 
writing to U.S. Department of Transportation, Subsequent Distribution 
Center, SVC-121.23, Ardmore East Business Center, 3341 Q 75th Avenue, 
Landover, Maryland 20785. The AC also will be available on the Internet 
at http://www.faa.gov/avr/air/airhome.htm, at the link titled 
``Advisory Circulars'' under the ``Available Information'' drop-down 
menu.

FOR FURTHER INFORMATION CONTACT: For technical issues contact Brent 
Bandley, FAA, Transport Airplane Directorate, Los Angeles Aircraft 
Certification Office, Airframe Branch, ANM-120L, 3960 Paramount 
Boulevard, Lakewood, California 90712-4137; telephone (562) 627-5237; 
fax (562) 627-5210.
    For other information contact: Jill DeMarco, FAA, Transport 
Airplane Directorate, Program Management Branch, ANM-114, 1601 Lind 
Avenue SW., Renton, Washington 98055-4056; telephone (425) 227-1313; 
fax (425) 227-1320.

SUPPLEMENTARY INFORMATION:

Discussion of Comments

    On December 22, 1997, the FAA issued a notice of the availability 
of proposed Advisory Circular (AC) 120-XX, ``Repair Assessment of 
Pressurized Fuselages.'' That notice was published in the Federal 
Register on January 2, 1998 (63 FR 137), and we requested comments from 
the public on the proposed AC document. Three commenters sent comments 
asking for changes to various sections of the proposed AC. We have 
addressed those comments in the final AC as described below.

Changes in General Terminology

    One commenter requests that the FAA clarify the terminology used in 
the proposed AC to indicate that the area of inspection termed the 
``fuselage pressure boundary.'' The commenter states that this area 
includes not only the fuselage skin and bulkhead web, but the door skin 
as well.
    The FAA concurs. The intent of the repair assessment is to include 
the entire fuselage pressure boundary, which does include, among other 
things, the fuselage, bulkhead webs, and the door skin. We have changed 
the terminology accordingly throughout the final AC. [We made this same 
change in terminology in the final rule associated with this AC: Repair 
Assessment for Pressurized Fuselages, amendments 91-264, 121-275, 125-
33, and 129-8 (65 FR 24108, April 25, 2000).]

Stage 1: Data Collection

    One commenter suggests changes to the guidance that concerns the 
list of structure for which repair assessments are required. The 
proposed guidance states that some manufacturers have reduced this list 
by determining the inspection requirements for critical details. If the 
requirements are equal to normal maintenance checks, such as the 
Baseline Zonal Inspection (BZI), those details were excluded from this 
list. The commenter points out that some manufacturers also have 
excluded items from the list if, through any other inspection program, 
the repaired structure was previously found to be damage-tolerant. The 
commenter requests that this be noted in the proposed AC.
    The FAA concurs. We have revised paragraph 5.a.(1) of the final AC 
accordingly.

Stage 2: Repair Classification

    One commenter notes the guidance states that, during ``Stage 2: 
Repair Classification,'' applicants would use information collected 
from ``a survey form'' to classify repairs (into one of three 
categories). The commenter states that, while filling in a survey form 
may be helpful when it is time to classify repairs, such a form is not 
necessary. Based on the knowledge of those doing the assessment, the 
classification could be done without filling in a survey form. 
Therefore, the commenter requests that the FAA revise the language in 
the proposed AC to state more generally that the applicant may use the 
information gathered during Stage 1 to classify repairs.
    The FAA concurs. We have revised the wording in paragraph 5.a.(2) 
of the final AC accordingly.

Category C Repairs

    One commenter requests that the term ``temporary'' be further 
defined to mean ``time-limited'' when defining Category C repairs. The 
commenter points to an FAA letter (ANM-120S:SCF, dated February 12, 
1990) that it previously received that provided three definitions of 
repairs. The definition contained in the letter that was most closely 
correlated to the definition of Category C repairs contained in the 
proposed AC, used the term ``time-limited'' to describe the repair, not 
``temporary.''

[[Page 9622]]

    The FAA concurs with the commenter's request. We have revised 
paragraph 5.a.(2)(c) of the final AC to state: ``Category C: A 
temporary (time-limited) repair that will need to be reworked or 
replaced prior to an established time * * *''

Airplane Cycle Age Equal to or Less Than Implementation Time on 
Effective Date of Rule

    One commenter requests that the FAA clarify the guidance on when 
the assessment process would begin for airplanes whose flight cycle age 
is equal to or less than the implementation time on the date the 
associated final rule becomes effective. Specifically, the commenter 
points out that the deadline for repair assessment does not include a 
``not to exceed'' value like the other airplanes addressed in the 
proposed AC.
    The FAA concurs that clarification is necessary. We have changed 
paragraph 6.g.(1) of the final AC to state that the assessment of an 
airplane in this group should take place before it exceeds the design 
service goal (DSG), plus an equivalent C-check. (This is parallel to 
the limit of the assessment deadline specified in paragraph 6.g.(2) for 
airplanes whose cycle age is greater than the implementation time, but 
less than the DSG, on the date that the associated final rule became 
effective.)

Maintenance Program Changes

    One commenter requests that the FAA revise the proposed AC to make 
its intent clearer concerning maintenance program changes. The proposed 
wording states: ``If the interval escalation reduces the frequency of 
inspection of the affected area below the BZI * * *''.
    The commenter considers that this wording is confusing, and 
suggests that it could be clearer if changed to: ``If the revised 
maintenance or inspection program intervals are greater than those in 
the BZI * * *''
    The FAA concurs. We have changed the wording in paragraph 6.h. of 
the final AC accordingly.

Sale and Transfer of Airplanes

    One commenter requests changes concerning the time for implementing 
the required repair assessment for airplanes that previously have been 
operated under an FAA-approved maintenance program and are now being 
sold or transferred. The commenter requests that the phrase, ``* * * 
whichever would result in an earlier accomplishment date for the 
assessment,'' be eliminated. The commenter states:
     Such a requirement to adopt previous operators' programs 
into the new operator's FAA-approved program adds needless 
administrative complexity and confusion.
     The FAA applies specific oversight of maintenance program 
integration for fleet additions, whether by acquisition of new or used 
aircraft of by lease.
     Ample FAA guidelines cover the integration of airplanes 
transitioning from one maintenance program to another, and there is no 
need to add an across-the-board provision which may not be appropriate 
in may cases.
    The FAA does not concur. We consider it essential that operators 
ensure that transferred airplanes are maintained in accordance with the 
repair assessment program on the same basis as if there were continuity 
in ownership. Scheduling of the repair assessments for each airplane 
must not be delayed or postponed because of a transfer of ownership; in 
some cases, such postponement could continue indefinitely if an 
airplane is transferred frequently from one owner to another. The 
stipulation contained in the AC is intended to prevent the situation 
where an airplane is transferred so often that it never gets assessed.

Miscellaneous Changes

    Title of AC: We changed the title of the final AC to ``Damage 
Tolerance Assessment of Repairs to Pressurized Fuselages.'' We consider 
that this new title more clearly reflects the content of the AC and the 
guidance provided.
    Paragraph 3., Discussion: We revised this paragraph in the final AC 
provide a comprehensive list of all airplane models that are subject to 
the requirements of 14 CFR parts 91, 121, 125, and 129 for a structural 
integrity assessment of repairs to the fuselage pressure boundary.
    Paragraph 6.j., Operation of Leased Foreign-Owned Airplanes: We 
revised this paragraph to point out that the applicant is not required 
to implement the assessment program only in accordance with the 
``model-specific manufacturer's repair assessment guidelines.'' We 
deleted the word ``manufacturer's'' from that phrase in the final AC. 
The applicant may use the manufacturer's guidelines or may use any 
others that have been developed and approved for the specific airplane 
model.

    Issued in Renton, Washington, on January 23, 2001.
Dorenda D. Baker,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 01-3309 Filed 2-7-01; 8:45 am]
BILLING CODE 4915-13-U