DEPARTMENT OF TRANSPORTATION
FEDERAL AVIATION ADMINISTRATION
14 CFR Part 39
[Docket No. FAA-2010-0037; Directorate Identifier 2009-NM-240-AD] RIN
2120-AA64
AIRWORTHINESS DIRECTIVES; The Boeing Company Model 737-700 (IGW) Series
Airplanes Equipped With Auxiliary Fuel Tanks Installed in Accordance With
Configuration 3 of Supplemental Type Certificate ST00936NY
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 cer-
tain Model 737-700 (IGW) series airplanes. This proposed AD would require
deactivation or modification of PATS Aircraft, LLC, auxiliary fuel tanks.
This proposed AD results from fuel system reviews conducted by the manu-
facturer. We are proposing this AD to prevent the potential of ignition
sources inside fuel tanks, which, in combination with flammable fuel vap-
ors, could result in fuel tank explosions and consequent loss of the air-
plane.
DATES: We must receive comments on this proposed AD by March 29, 2010.
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 proposed AD, contact Decrane
Aerospace, PATS Aircraft Systems, 21652 Nanticoke Avenue, Georgetown,
Delaware 19947; telephone 302-253-6157; fax 302-855-0153; e-mail
giuseppecoppola@decraneaerospace.com; Internet http://www.decraneaerospace
.com. You may review copies of the referenced service information at the
FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton,
Washington. For information on the availability of this material at the
FAA, call 425-227-1221 or 425-227-1152.
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: Mazdak Hobbi, Aerospace Engineer, Propul-
sion and Services Branch, ANE-173, FAA, New York Aircraft Certification
Office, 1600 Stewart Avenue, Suite 410, Westbury, New York 11590;
telephone (516) 228-7330; fax (516) 794-5531.
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-2010-0037; Directorate
Identifier 2009-NM-240-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.
SUPPLEMENTAL TYPE CERTIFICATES (STCS) FOR PATS AIRCRAFT, LLC, AUXILIARY
FUEL TANKS
The auxiliary fuel tank STC on affected airplanes is of two basic type
designs: A box-and-bladder type, and a double-walled cylindrical type. The
box-and-bladder tanks are emptied and vented into the airplane center wing
tank using either pneumatic air pressure supplied from the airplane, or
electrical power from the airplane to power fuel pumps installed in the
tank external dry bay area. The double-walled cylindrical tanks use
pneumatic air pressure to empty into the airplane center wing tank. All
auxiliary tanks use some type of electrical fuel quantity indication
system (FQIS), flight deck control and annunciation panels, float level
switches, valves and venting systems, electrical wiring connections in the
dry bay area, and electrical bonding methods.
FAA'S FINDINGS
During the SFAR 88 safety assessment, it was determined that the PATS
Aircraft, LLC, FQIS and float level switch did not meet intrinsically safe
electrical energy levels as described in the guidelines of Advisory
Circular (AC) 25.981-1C, "Fuel Tank Ignition Source Prevention
Guidelines." PATS Aircraft, LLC, the STC holder, identified potential
ignition sources resulting from a combination of single and latent
failures for the PATS Aircraft, LLC, fuel tank subsystems. PATS Aircraft,
LLC, has not complied with the requirements of SFAR 88, paragraph 2. To
prevent high electrical energy levels from the FQIS and float level switch
from entering the auxiliary fuel tank, we have determined that the
appropriate solution for continued use is a combination of actions.
Installing a transient suppression device (TSD) on FQIS and float level
switches would be needed. In order to maximize wire separation, the TSD
must be installed as close as possible to the points where the FQIS and
float level switch wires exit the TSD and enter the auxiliary tank. Other
actions might include replacing high-energy FQISs, and float level
switches that are impractical for TSD application, with intrinsically safe
FQISs, providing wire separation, conducting a one-time inspection and/or
replacing aging float level switch conduit assemblies, periodically
inspecting the external dry bay system components and wires, and testing
the integrity of bonding resistances.
As an alternative to the modification described above, deactivation of the
auxiliary fuel tanks would adequately address the unsafe condition. If
operators do not wish to deactivate their auxiliary fuel tanks, we will
consider requests for alternative methods of compliance (AMOCs). The most
likely requests would be to allow continued use of the tanks by showing
compliance with SFAR 88. This would involve obtaining STCs to modify the
auxiliary fuel tank systems and developing maintenance procedures to
address the safety issues identified above. PATS Aircraft, LLC, as the
current STC holder, may be working on AMOCs. Operators may contact PATS or
propose an AMOC on their own.
Once an operator has deactivated a tank as proposed by this NPRM, the
operator might wish to remove the tank. This would require a separate
design approval, if an approved tank removal procedure does not exist.
RELEVANT SERVICE INFORMATION
We have reviewed Decrane Aerospace Service Bulletins ST00936NY-D-28-SB
-001--K, dated August 25, 2008; and ST00936NY-D-28-SB-021--K, dated
January 8, 2009; which describe procedures for modifying the auxiliary
fuel system (AFS). The modification of the auxiliary fuel cells of the AFS
specified in Decrane Aerospace Service Bulletin ST00936NY-D-28-SB-001--K
includes removing, repositioning, replacing or adding bonding jumpers
and/or hardware. The modification of the AFS harnesses specified in
Decrane Aerospace Service Bulletin ST00936NY-D-28-SB-021--K includes
removing and replacing the auxiliary fuel system critical harnesses.
FAA'S DETERMINATION AND REQUIREMENTS OF THE PROPOSED AD
We have evaluated all pertinent information and identified an unsafe
condition that is likely to exist or develop on other products of this
same type design. For this reason, we are proposing this AD, which would
require deactivation to prevent usage of auxiliary fuel tanks, or
modification of the auxiliary fuel system.
COSTS OF COMPLIANCE
We estimate that this proposed AD would affect 11 airplanes of U.S.
registry. We also estimate that it would take about 250 work-hours per
product to comply with this proposed AD. The average labor rate is $85 per
work-hour. Required parts would cost about $10,000 per product. Based on
these figures, we estimate the cost of this proposed AD to the U.S.
operators to be $343,750, or $31,250 per product.
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 responsib-
ilities 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 Proc-
edures (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, Incorporation by reference,
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: