Airworthiness Directives; Boeing Model 747 Series Airplanes

[Federal Register Volume 61, Number 252 (Tuesday, December 31, 1996)]
[Rules and Regulations]
[Pages 69026-69027]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 96-33041]


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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. 96-NM-279-AD; Amendment 39-9867; AD 96-26-04]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 747 Series Airplanes

AGENCY: Federal Aviation Administration, DOT.

ACTION: Final rule; request for comments.

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SUMMARY: This amendment adopts a new airworthiness directive (AD) that 
is applicable to certain Boeing Model 747 series airplanes. This action 
requires a one-time inspection to detect fatigue cracking of the 
vertical beam webs and chords of the nose wheel well (NWW) at body 
station (BS) 300 and BS 320, and repair, if necessary. This action also 
requires inspections to detect fatigue cracking of the inner chord and 
web of the fuselage frames at BS 300 and BS 320, and repair, if 
necessary. This amendment is prompted by a report indicating that the 
fuselage frames at BS 300 and BS 320 severed approximately 10 inches 
outboard of the NWW side panel and resulted in accelerated fatigue 
cracking and subsequent failure of the adjacent NWW vertical beams. The 
actions specified in this AD are intended to detect and correct such 
fatigue cracking, which could result in collapse of the NWW pressure 
bulkhead and subsequent rapid decompression of the airplane.

DATES: Effective January 6, 1997.
    Comments for inclusion in the Rules Docket must be received on or 
before March 3, 1997.

ADDRESSES: Submit comments in triplicate to the Federal Aviation 
Administration (FAA), Transport Airplane Directorate, ANM-103, 
Attention: Rules Docket No. 96-NM-279-AD, 1601 Lind Avenue, SW., 
Renton, Washington 98055-4056.

FOR FURTHER INFORMATION CONTACT: Bob Breneman, Aerospace Engineer, 
Airframe Branch, ANM-120S, FAA, Seattle Aircraft Certification Office, 
1601 Lind Avenue, SW., Renton, Washington; telephone (206) 227-2776; 
fax (206) 227-1181.

SUPPLEMENTARY INFORMATION: The FAA has received a report indicating 
that the flight crew of a Boeing Model 747-200 series airplane heard a 
loud noise below the cockpit area during flight descent. The flight 
continued with an uneventful landing. Investigation revealed that the 
left-hand side wall of the nose wheel well (NWW) was bulging. Further 
investigation revealed that the fuselage frames at body stations (BS) 
300 and BS 320 had severed approximately 10 inches outboard of the NWW 
side panel. Additionally, the vertical beam of the NWW at BS 300 
contained multiple cracks in the inner chord, a severed web, and a 
cracked and deformed outer chord. The vertical beam of the NWW at BS 
320 also was found to have a severed web and cracks in the radius of 
the inner chord, as well as severe damage to numerous horizontal 
stiffeners and clips. The apparent cause of this cracking is fatigue.
    Fatigue cracking of the BS 300 and BS 320 fuselage frames in the 
area of the NWW, if not detected and corrected in a timely manner, 
could result in collapse of the NWW pressure bulkhead, and subsequent 
rapid decompression of the airplane.

Other Relevant Rulemaking

    The FAA previously issued AD 90-06-14, amendment 39-6544 (55 FR 
10045, March 19, 1990), which is applicable to certain Boeing Model 747 
series airplanes. [A correction of that rule was published in the 
Federal Register on May 18, 1990 (55 FR 20590).] That AD requires 
repetitive visual inspections to detect fatigue cracking of the 
vertical beams, webs, clips, side wall web, top panel and intercostals 
of the NWW. That AD requires that the initial inspection be 
accomplished prior to the accumulation of 10,000 total flight cycles, 
and that repetitive inspections be accomplished at intervals of 1,500 
or 3,000 flight cycles, depending on the inspection method used.
    The FAA also issued AD 91-11-01, amendment 39-6997 (56 FR 22306, 
May 15, 1991), which also is applicable to certain Boeing Model 747 
series airplanes. That AD requires the inspection to detect fatigue 
cracking of the fuselage frames adjacent to the NWW, prior to the 
accumulation of 16,000 flight cycles. That AD provides an optional 
terminating modification that entails installing new fuselage frames 
(including the frames adjacent to the NWW) with improved durability. 
That modification is required prior to the accumulation of 20,000 
flight cycles in accordance with AD 90-06-06 (aging fleet AD).
    The airplane involved in the incident described previously had 
accumulated 14,341 total flight cycles at the time of structural 
failure. A visual inspection to detect cracking of the vertical beams 
of the NWW in accordance with AD 90-06-14 had been performed only 621 
cycles prior to the reported failure. The fuselage frames in its NWW 
area had not yet been replaced with the new, improved durability frames 
in accordance with AD 91-11-01.

Explanation of the Requirements of the Rule

    Since an unsafe condition has been identified that is likely to 
exist or develop on other Boeing Model 747 series airplanes of the same 
type design, this AD is being issued to detect and correct fatigue 
cracking of BS 300 and BS 320 fuselage frames adjacent to the NWW, 
which could result in collapse of the NWW pressure bulkhead and 
possibly result in rapid decompression of the airplane. This AD 
requires repetitive visual inspections to detect fatigue cracking of 
the inner chord and web of the left and right side of fuselage frames 
at BS 300 and BS 320, from the NWW side panel outboard to stringer 39. 
This AD also requires a one-time visual inspection to detect fatigue 
cracking of the vertical beam webs and chords of the NWW at BS 300 and 
BS 320. This AD also requires that any cracking detected during those 
inspections be repaired in accordance with a method approved by the 
FAA.

Interim Action

    This is considered to be interim action until final action is 
identified, at which time the FAA may consider further rulemaking.

Determination of Rule's Effective Date

    Since a situation exists that requires the immediate adoption of 
this regulation, it is found that notice and opportunity for prior 
public comment hereon are impracticable, and that good cause exists for 
making this amendment effective in less than 30 days.

Comments Invited

    Although this action is in the form of a final rule that involves 
requirements affecting flight safety and, thus, was not preceded by 
notice and an opportunity for public comment, comments are invited on 
this rule. Interested persons are invited to comment on this rule by 
submitting such written data, views, or arguments as they may desire. 
Communications shall identify the

[[Page 69027]]

Rules Docket number and be submitted in triplicate to the address 
specified under the caption ADDRESSES. All communications received on 
or before the closing date for comments will be considered, and this 
rule may be amended in light of the comments received. Factual 
information that supports the commenter's ideas and suggestions is 
extremely helpful in evaluating the effectiveness of the AD action and 
determining whether additional rulemaking action would be needed.
    Comments are specifically invited on the overall regulatory, 
economic, environmental, and energy aspects of the rule that might 
suggest a need to modify the rule. All comments submitted will be 
available, both before and after the closing date for comments, in the 
Rules Docket for examination by interested persons. A report that 
summarizes each FAA-public contact concerned with the substance of this 
AD will be filed in the Rules Docket.
    Commenters wishing the FAA to acknowledge receipt of their comments 
submitted in response to this rule must submit a self-addressed, 
stamped postcard on which the following statement is made: ``Comments 
to Docket Number 96-NM-279-AD.'' The postcard will be date stamped and 
returned to the commenter.

Regulatory Impact

    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.
    The FAA has determined that this regulation is an emergency 
regulation that must be issued immediately to correct an unsafe 
condition in aircraft, and that it is not a ``significant regulatory 
action'' under Executive Order 12866. It has been determined further 
that this action involves an emergency regulation under DOT Regulatory 
Policies and Procedures (44 FR 11034, February 26, 1979). If it is 
determined that this emergency regulation otherwise would be 
significant under DOT Regulatory Policies and Procedures, a final 
regulatory evaluation will be prepared and placed in the Rules Docket. 
A copy of it, if filed, 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, 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. 106(g), 40113, 44701.

Sec. 39.13  [Amended]

    2. Section 39.13 is amended by adding the following new 
airworthiness directive:
96-26-04 Boeing: Amendment 39-9867. Docket 96-NM-279-AD.

    Applicability: Model 747 series airplanes having line numbers 1 
through 678 inclusive; on which the Section 41 frame replacement in 
zone 1 specified in Boeing Service Bulletin 747-53-2272 has not been 
accomplished; certificated in any category.

    Note 1: This AD applies to each airplane identified in the 
preceding applicability provision, regardless of whether it has been 
otherwise modified, altered, or repaired in the area subject to the 
requirements of this AD. For airplanes that have been modified, 
altered, or repaired so that the performance of the requirements of 
this AD is affected, the owner/operator must request approval for an 
alternative method of compliance in accordance with paragraph (c) of 
this AD. The request should include an assessment of the effect of 
the modification, alteration, or repair on the unsafe condition 
addressed by this AD; and, if the unsafe condition has not been 
eliminated, the request should include specific proposed actions to 
address it.

    Compliance: Required as indicated, unless accomplished 
previously.
    To detect and correct fatigue cracking of body station (BS) 300 
and BS 320 fuselage frames adjacent to the nose wheel well (NWW), 
which could result in collapse of the NWW pressure bulkhead, and 
subsequent rapid decompression of the airplane, accomplish the 
following:
    (a) Prior to the accumulation of 10,000 total flight cycles, or 
within 50 flight cycles after the effective date of this AD, 
whichever occurs later, perform a detailed visual inspection to 
detect fatigue cracking of the inner chord and web of the left side 
and right side of BS 300 and BS 320 fuselage frames from the nose 
wheel well (NWW) side panel outboard to stringer 39, in accordance 
with normal maintenance practices. Pay particular attention to the 
area where the NWW vertical beam inner chord interfaces with the 
fuselage frame.
    (1) If no cracking is detected, repeat the detailed visual 
inspection thereafter at intervals not to exceed 100 flight cycles.
    (2) If any cracking is detected, prior to further flight, repair 
in accordance with a method approved by the Manager, Seattle 
Aircraft Certification Office (ACO), FAA, Transport Airplane 
Directorate.
    (b) Prior to the accumulation of 10,000 total flight cycles, or 
within 50 flight cycles after the effective date of this AD, 
whichever occurs later, perform a detailed one-time visual 
inspection to detect fatigue cracking of the left and right side 
vertical beam webs and chords of the NWW at BS 300 and BS 320, in 
accordance with normal maintenance procedures.
    (1) If no cracking is detected, no further action is required by 
this paragraph.
    (2) If any cracking is detected, prior to further flight, repair 
in accordance with a method approved by the Manager, Seattle ACO.
    (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) This amendment becomes effective on January 6, 1997.

    Issued in Renton, Washington, on December 20, 1996.
S. R. Miller,
Acting Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. 96-33041 Filed 12-30-96; 8:45 am]
BILLING CODE 4910-13-U

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