[Federal Register Volume 73, Number 111 (Monday, June 9, 2008)]
[Proposed Rules]
[Pages 32491-32493]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: E8-12829]



[[Page 32491]]

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DEPARTMENT OF TRANSPORTATION

Federal Aviation Administration

14 CFR Part 39

[Docket No. FAA-2008-0621; Directorate Identifier 2008-NM-015-AD]
RIN 2120-AA64


Airworthiness Directives; Boeing Model 737-600, -700, -800, and -
900 Series Airplanes

AGENCY: Federal Aviation Administration (FAA), DOT.

ACTION: Notice of proposed rulemaking (NPRM).

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SUMMARY: We propose to adopt a new airworthiness directive (AD) for 
certain Boeing Model 737-600, -700, -800, and -900 series airplanes. 
This proposed AD would require installation of hot short protector 
(HSP) support brackets and equipment for the fuel quantity indicating 
system (FQIS) fuel densitometer and other specified actions as 
applicable. This proposed AD would also require a revision to the 
Airworthiness Limitations (AWLs) section of the Instructions for 
Continued Airworthiness to incorporate AWL No. 28-AWL-07. This proposed 
AD results from fuel system reviews conducted by the manufacturer. We 
are proposing this AD to prevent the center tank fuel densitometer from 
overheating and becoming a potential ignition source inside the center 
fuel tank, which, in combination with flammable fuel vapors, could 
result in a center fuel tank explosion and consequent loss of the 
airplane.

DATES: We must receive comments on this proposed AD by July 24, 2008.

ADDRESSES: You may send comments by any of the following methods:
     Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.
     Fax: 202-493-2251.
     Mail: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue, SE., Washington, DC 20590.
     Hand Delivery: U.S. Department of Transportation, Docket 
Operations, M-30, West Building Ground Floor, Room W12-140, 1200 New 
Jersey Avenue, SE., Washington, DC 20590, between 9 a.m. and 5 p.m., 
Monday through Friday, except Federal holidays.
    For service information identified in this AD, contact Boeing 
Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124-2207.

Examining the AD Docket

    You may examine the AD docket on the Internet at http://www.regulations.gov; or in person at the Docket Management Facility 
between 9 a.m. and 5 p.m., Monday through Friday, except Federal 
holidays. The AD docket contains this proposed AD, the regulatory 
evaluation, any comments received, and other information. The street 
address for the Docket Office (telephone 800-647-5527) is in the 
ADDRESSES section. Comments will be available in the AD docket shortly 
after receipt.

FOR FURTHER INFORMATION CONTACT: Georgios Roussos, Aerospace Engineer, 
Systems and Equipment Branch, ANM-130S, FAA, Seattle Aircraft 
Certification Office, 1601 Lind Avenue, SW., Renton, Washington 98057-
3356; telephone (425) 917-6482; fax (425) 917-6590.

SUPPLEMENTARY INFORMATION:

Comments Invited

    We invite you to send any written relevant data, views, or 
arguments about this proposed AD. Send your comments to an address 
listed under the ADDRESSES section. Include ``Docket No. FAA-2008-0621; 
Directorate Identifier 2008-NM-015-AD'' at the beginning of your 
comments. We specifically invite comments on the overall regulatory, 
economic, environmental, and energy aspects of this proposed AD. We 
will consider all comments received by the closing date and may amend 
this proposed AD because of those comments.
    We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We 
will also post a report summarizing each substantive verbal contact we 
receive about this proposed AD.

Discussion

    The FAA has examined the underlying safety issues involved in fuel 
tank explosions on several large transport airplanes, including the 
adequacy of existing regulations, the service history of airplanes 
subject to those regulations, and existing maintenance practices for 
fuel tank systems. As a result of those findings, we issued a 
regulation titled ``Transport Airplane Fuel Tank System Design Review, 
Flammability Reduction and Maintenance and Inspection Requirements'' 
(66 FR 23086, May 7, 2001). In addition to new airworthiness standards 
for transport airplanes and new maintenance requirements, this rule 
included Special Federal Aviation Regulation No. 88 (``SFAR 88,'' 
Amendment 21-78, and subsequent Amendments 21-82 and 21-83).
    Among other actions, SFAR 88 requires certain type design (i.e., 
type certificate (TC) and supplemental type certificate (STC)) holders 
to substantiate that their fuel tank systems can prevent ignition 
sources in the fuel tanks. This requirement applies to type design 
holders for large turbine-powered transport airplanes and for 
subsequent modifications to those airplanes. It requires them to 
perform design reviews and to develop design changes and maintenance 
procedures if their designs do not meet the new fuel tank safety 
standards. As explained in the preamble to the rule, we intended to 
adopt airworthiness directives to mandate any changes found necessary 
to address unsafe conditions identified as a result of these reviews.
    In evaluating these design reviews, we have established four 
criteria intended to define the unsafe conditions associated with fuel 
tank systems that require corrective actions. The percentage of 
operating time during which fuel tanks are exposed to flammable 
conditions is one of these criteria. The other three criteria address 
the failure types under evaluation: Single failures, single failures in 
combination with a latent condition(s), and in-service failure 
experience. For all four criteria, the evaluations included 
consideration of previous actions taken that may mitigate the need for 
further action.
    We have determined that the actions identified in this AD are 
necessary to reduce the potential of ignition sources inside fuel 
tanks, which, in combination with flammable fuel vapors, could result 
in fuel tank explosions and consequent loss of the airplane.
    Boeing has found that no separation was provided for the fuel 
quantity indication system (FQIS) wires. A potential hot short of the 
FQIS lead wire could cause the center fuel tank densitometer to 
overheat. In situations where the fuel level in the center tank is low, 
the overheated densitometer could ignite flammable fuel vapors inside 
the center fuel tank. This condition, if not corrected, could result in 
a center fuel tank explosion and consequent loss of the airplane.

Other Related Rulemaking

    On April 29, 2008, we issued AD 2008-10-10, amendment 39-15516 (73 
FR 25986, May 8, 2008), applicable to certain Boeing Model 737-600, -
700, -700C, -800, and -900 series airplanes. That AD requires revising 
the Airworthiness Limitations (AWLs) section of the Instructions for 
Continued

[[Page 32492]]

Airworthiness (ICA) by incorporating new limitations for fuel tank 
systems to satisfy SFAR 88 requirements. That AD also requires the 
initial inspection of a certain repetitive AWL inspection to phase in 
that inspection, and repair if necessary. That AD resulted from a 
design review of the fuel tank systems. We issued that AD to prevent 
the potential for ignition sources inside fuel tanks caused by latent 
failures, alterations, repairs, or maintenance actions, which, in 
combination with flammable fuel vapors, could result in a fuel tank 
explosion and consequent loss of the airplane. Incorporating AWL No. 
28-AWL-07 into the AWLs section of the ICA in accordance with paragraph 
(g)(3) of AD 2008-10-10 would terminate the action specified in 
paragraph (g) of this proposed AD.

Relevant Service Information

    We have reviewed Boeing Alert Service Bulletin 737-28A1221, 
Revision 1, dated November 9, 2007. The service bulletin describes 
procedures for installing hot short protector (HSP) support brackets 
and equipment for the FQIS fuel densitometer and doing other specified 
actions as applicable. The other specified actions include installing 
wire bundle and ground stud support brackets, replacing certain wire 
bundle support brackets with new brackets, installing new support 
clamps and wire bundles, and rerouting certain wire bundles.
    We have also reviewed Revision March 2007 R2 of Section 9 of the 
Boeing 737-600/700/800/900 Maintenance Planning Data (MPD) Document, 
D626A001-CMR (hereafter referred to as ``the MPD''). Subsection F, 
``AIRWORTHINESS LIMITATIONS--FUEL SYSTEM AWLs,'' of the MPD describes 
AWLs for fuel tank systems. Subsection F of the MPD includes fuel 
system AWL No. 28-AWL-07, which is a critical design configuration 
control limitation (CDCCL) to maintain the design features of the 
center fuel tank HSP during its replacement.

FAA's Determination and Requirements of This Proposed AD

    We are proposing this AD because we evaluated all relevant 
information and determined the unsafe condition described previously is 
likely to exist or develop in other products of the(se) same type 
design(s). This proposed AD would require the following actions:
     Installing HSP equipment for the FQIS fuel densitometer 
and doing other specified actions as applicable.
     Revising the AWLs section of the ICA to incorporate AWL 
No. 28-AWL-07, which would require maintaining the design features of 
the center fuel tank HSP during its replacement.
    This proposed AD would also allow accomplishing the revision to the 
AWLs section of the ICA in accordance with later revisions of the MPD 
as an acceptable method of compliance if they are approved by the 
Manager, Seattle Aircraft Certification Office, FAA.

Costs of Compliance

    We estimate that this proposed AD would affect 13 airplanes of U.S. 
registry. The following table provides the estimated costs, at an 
average labor rate of $80 per work hour, for U.S. operators to comply 
with this proposed AD.

                                                 Estimated Costs
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                                                                                 Number of U.S.-
           Action                Work hours         Parts           Cost per       registered       Fleet cost
                                                                    airplane        airplanes
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Installation of HSP support   Up to 16.......  Up to $14,698..  Up to $15,978..              13  Up to $207,714.
 brackets and equipment.
AWLs revision...............  1..............  None...........  $80............              13  $1,040.
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Authority for This Rulemaking

    Title 49 of the United States Code specifies the FAA's authority to 
issue rules on aviation safety. Subtitle I, section 106, describes the 
authority of the FAA Administrator. ``Subtitle VII: Aviation 
Programs,'' describes in more detail the scope of the Agency's 
authority.
    We are issuing this rulemaking under the authority described in 
``Subtitle VII, Part A, Subpart III, Section 44701: General 
requirements.'' Under that section, Congress charges the FAA with 
promoting safe flight of civil aircraft in air commerce by prescribing 
regulations for practices, methods, and procedures the Administrator 
finds necessary for safety in air commerce. This regulation is within 
the scope of that authority because it addresses an unsafe condition 
that is likely to exist or develop on products identified in this 
rulemaking action.

Regulatory Findings

    We determined that this proposed AD would not have federalism 
implications under Executive Order 13132. This proposed AD would not 
have a substantial direct effect 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.
    For the reasons discussed above, I certify this proposed 
regulation:
    1. Is not a ``significant regulatory action'' under Executive Order 
12866,
    2. Is not a ``significant rule'' under the 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.
    You can find our regulatory evaluation and the estimated costs of 
compliance in the AD Docket.

List of Subjects in 14 CFR Part 39

    Air transportation, Aircraft, Aviation safety, Safety.

The Proposed Amendment

    Accordingly, under the authority delegated to me by the 
Administrator, the FAA proposes to amend 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. The FAA amends Sec.  39.13 by adding the following new AD:

Boeing: Docket No. FAA-2008-0621; Directorate Identifier 2008-NM-
015-AD.

Comments Due Date

    (a) We must receive comments by July 24, 2008.

Affected ADs

    (b) None.

Applicability

    (c) This AD applies to Boeing Model 737-600, -700, -800, and -
900 series airplanes, certificated in any category; as identified in

[[Page 32493]]

Boeing Alert Service Bulletin 737-28A1221, Revision 1, dated 
November 9, 2007.

    Note 1: This AD requires revisions to certain operator 
maintenance documents to include new inspections. Compliance with 
these inspections is required by 14 CFR 91.403(c). For airplanes 
that have been previously modified, altered, or repaired in the 
areas addressed by these inspections, the operator may not be able 
to accomplish the inspections described in the revisions. In this 
situation, to comply with 14 CFR 91.403(c), the operator must 
request approval for an alternative method of compliance (AMOC) 
according to paragraph (k) of this AD. The request should include a 
description of changes to the required inspections that will ensure 
the continued operational safety of the airplane.

Unsafe Condition

    (d) This AD results from fuel system reviews conducted by the 
manufacturer. We are issuing this AD to prevent the center tank fuel 
densitometer from overheating and becoming a potential ignition 
source inside the center fuel tank, which, in combination with 
flammable fuel vapors, could result in a center fuel tank explosion 
and consequent loss of the airplane.

Compliance

    (e) Comply with this AD within the compliance times specified, 
unless already done.

Installation of the Hot Short Protector (HSP)

    (f) Within 60 months after the effective date of this AD, 
install the HSP support brackets and equipment for the fuel quantity 
indicating system (FQIS) fuel densitometer and do all the other 
specified actions as applicable, by accomplishing all of the 
applicable actions specified in the Accomplishment Instructions of 
Boeing Alert Service Bulletin 737-28A1221, Revision 1, dated 
November 9, 2007.

Airworthiness Limitations (AWLs) Revision for AWL No. 28-AWL-07

    (g) Concurrently with accomplishing the actions required by 
paragraph (f) of this AD, revise the AWLs section of the 
Instructions for Continued Airworthiness (ICA) by incorporating AWL 
No. 28-AWL-07 of Subsection F of the Boeing 737-600/700/800/900 
Maintenance Planning Data (MPD) Document, D626A001-CMR, Section 9, 
Revision March 2007 R2 (hereafter referred to as ``the MPD'').

No Alternative Critical Design Configuration Control Limitations 
(CDCCLs)

    (h) After accomplishing the action specified in paragraph (g) of 
this AD, no alternative CDCCLs may be used unless the CDCCLs are 
part of a later revision of the MPD that is approved by the Manager, 
Seattle ACO; or unless the CDCCLs are approved as an AMOC in 
accordance with the procedures specified in paragraph (k) of this 
AD.

Credit for Actions Done According to Previous Issue of Service Bulletin

    (i) Actions done before the effective date of this AD in 
accordance with Boeing Alert Service Bulletin 737-28A1221, dated 
January 14, 2007, are acceptable for compliance with the 
requirements of paragraph (f) of this AD.

Terminating Action for AWLs Revision

    (j) Incorporating AWL No. 28-AWL-07 into the AWLs section of the 
ICA in accordance with paragraph (g)(3) of AD 2008-10-10, amendment 
39-15516, terminates the action required by paragraph (g) of this 
AD.

Alternative Methods of Compliance (AMOCs)

    (k)(1) The Manager, Seattle ACO, FAA, ATTN: Georgios Roussos, 
Aerospace Engineer, Systems and Equipment Branch, ANM-130S, 1601 
Lind Avenue, SW., Renton, Washington 98057-3356; telephone (425) 
917-6482; fax (425) 917-6590; has the authority to approve AMOCs for 
this AD, if requested using the procedures found in 14 CFR 39.19.
    (2) To request a different method of compliance or a different 
compliance time for this AD, follow the procedures in 14 CFR 39.19. 
Before using any approved AMOC on any airplane to which the AMOC 
applies, notify your appropriate principal inspector (PI) in the FAA 
Flight Standards District Office (FSDO), or lacking a PI, your local 
FSDO.

    Issued in Renton, Washington, on May 30, 2008.
Ali Bahrami,
Manager, Transport Airplane Directorate, Aircraft Certification 
Service.
[FR Doc. E8-12829 Filed 6-6-08; 8:45 am]
BILLING CODE 4910-13-P