07MYR2 23086
Federal Register / Vol. 66, No. 88 / Monday, May 7, 2001 / Rules and Regulations
DEPARTMENT OF TRANSPORTATION
Federal Aviation Administration
14 CFR Parts 21, 25, 91, 121, 125, and
129
[Docket No. FAA19996411; Amendment
Nos. 2178, 25102, 91266, 121282, 125
36, 12930]
RIN 2120AG62
Transport Airplane Fuel Tank System
Design Review, Flammability
Reduction, and Maintenance and
Inspection Requirements
AGENCY
:
Federal Aviation
Administration (FAA), DOT.
ACTION
:
Final rule.
SUMMARY
:
This rule requires design
approval holders of certain turbine-
powered transport category airplanes,
and of any subsequent modifications to
these airplanes, to substantiate that the
design of the fuel tank system precludes
the existence of ignition sources within
the airplane fuel tanks. It also requires
developing and implementing
maintenance and inspection
instructions to assure the safety of the
fuel tank system. For new type designs,
this rule also requires demonstrating
that ignition sources cannot be present
in fuel tanks when failure conditions are
considered, identifying any safety-
critical maintenance actions, and
incorporating a means either to
minimize development of flammable
vapors in fuel tanks or to prevent
catastrophic damage if ignition does
occur. These actions are based on
accident investigations and adverse
service experience, which have shown
that unforeseen failure modes and lack
of specific maintenance procedures on
certain airplane fuel tank systems may
result in degradation of design safety
features intended to preclude ignition of
vapors within the fuel tank.
EFFECTIVE DATE
:
June 6, 2001.
FOR FURTHER INFORMATION CONTACT
:
Michael E. Dostert, FAA, Propulsion/
Mechanical Systems Branch, ANM112,
Transport Airplane Directorate, Aircraft
Certification Service, 1601 Lind Avenue
SW., Renton, Washington 980554056;
telephone (425) 2272132, facsimile
(425) 2271320; e-mail:
mike.dostert@faa.gov.
SUPPLEMENTARY INFORMATION
:
Availability of Final Rules
You can get an electronic copy using
the Internet by taking the following
steps:
(1) Go to the search function of the
Department of Transportations
electronic Docket Management System
(DMS) Web page (http://dms.dot.gov/
search).
(2) On the search page type in the last
four digits of the Docket number shown
at the beginning of this notice. Click on
search.
(3) On the next page, which contains
the Docket summary information for the
Docket you selected, click on the final
rule.
(4) To view or download the
document click on either Scanned
Image (TIFF) or Adobe PDF.
You can also get an electronic copy
using the Internet through FAAs web
page at http://www.faa.gov/avr/arm/
nprm/nprm.htm or the Federal
Registers web page at http://
www.access.gpo.gov/su
_
docs/aces/
aces140.html.
You can also get a copy by submitting
a request to the Federal Aviation
Administration, Office of Rulemaking,
ARM1, 800 Independence Avenue
SW., Washington, DC 20591, or by
calling (202) 2679680. Make sure to
identify the amendment number or
docket number of this final rule.
Small Business Regulatory Enforcement
Fairness Act
The Small Business Regulatory
Enforcement Fairness Act (SBREFA) of
1996 requires FAA to comply with
small entity requests for information or
advice about compliance with statutes
and regulations within its jurisdiction.
Therefore, any small entity that has a
question regarding this document may
contact their local FAA official, or the
person listed under
FOR FURTHER
INFORMATION CONTACT
. You can find out
more about SBREFA on the Internet at
our site, http://www.gov/avr/arm/
sbrefa.htm. For more information on
SBREFA, e-mail us at 9AWA
SBREFA@faa.gov.
Background
On October 26, 1999, the FAA issued
Notice of Proposed Rulemaking (NPRM)
9918, which was published in the
Federal Register on October 29, 1999
(64 FR 58644). That notice proposed
three separate requirements:
First, a requirement was proposed for
the design approval holders of certain
transport category airplanes to conduct
a safety review of the airplane fuel tank
system and to develop specific fuel tank
system maintenance and inspection
instructions for any items determined to
require repetitive inspections or
maintenance.
Second, a requirement was proposed
to prohibit the operation of those
airplanes beyond a specified time,
unless the operators of those airplanes
incorporated instructions for
maintenance and inspection of the fuel
tank system into their inspection
programs.
Third, for new designs, the proposal
included a requirement for minimizing
the flammability of fuel tanks, a
requirement concerning detailed failure
analysis to preclude the presence of
ignition sources in the fuel tanks and
including mandatory fuel system
maintenance in the limitations section
of the Instructions for Continued
Airworthiness.
Issues Prompting This Rulemaking
Activity
On July 17, 1996, a 25-year old Boeing
Model 747100 series airplane was
involved in an inflight breakup after
takeoff from Kennedy International
Airport in New York, resulting in 230
fatalities. The accident investigation
conducted by the National
Transportation Safety Board (NTSB)
indicated that the center wing fuel tank
exploded due to an unknown ignition
source. The NTSB issued
recommendations intended to: Reduce heating of the fuel in the
center wing fuel tanks on the existing
fleet of transport airplanes, Reduce or eliminate operation with
flammable vapors in the fuel tanks of
new type certificated airplanes, and Reevaluate the fuel system design
and maintenance practices on the fleet
of transport airplanes.
The accident investigation focused on
mechanical failure as providing the
energy source that ignited the fuel
vapors inside the tank.
The NTSB announced their official
findings of the TWA 800 accident at a
public meeting held August 2223,
2000, in Washington, DC. The NTSB
determined that the probable cause of
the explosion was ignition of the
flammable fuel/air mixture in the center
wing fuel tank. Although the ignition
source could not be determined with
certainty, the NTSB determined that the
most likely source was a short circuit
outside of the center wing tank that
allowed excessive voltage to enter the
tank through electrical wiring associated
with the fuel quantity indication system
(FQIS). Opening remarks at the hearing
also indicated that:
* * * This investigation and several others
have brought to light some broader issues
regarding aircraft certification. For example,
there are questions about the adequacy of the
risk analyses that are used as the basis for
demonstrating compliance with many
certification requirements.
This accident prompted the FAA to
examine the underlying safety issues
surrounding fuel tank explosions, the
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Federal Register / Vol. 66, No. 88 / Monday, May 7, 2001 / Rules and Regulations
adequacy of the existing regulations, the
service history of airplanes certificated
to these regulations, and existing
maintenance practices relative to the
fuel tank system.
Flammability Characteristics
The flammability characteristics of
the various fuels approved for use in
transport airplanes results in the
presence of flammable vapors in the
vapor space of fuel tanks at various
times during the operation of the
airplane. Vapors from Jet A fuel (the
typical commercial turbojet engine fuel)
at temperatures below approximately
100
°
F are too lean to be flammable at
sea level; at higher altitudes the fuel
vapors become flammable at
temperatures above approximately 45
°
F
(at 40,000 feet altitude).
However, the regulatory authorities
and aviation industry have always
presumed that a flammable fuel air
mixture exists in the fuel tanks at all
times and have adopted the philosophy
that the best way to ensure airplane fuel
tank safety is to preclude ignition
sources within fuel tanks. This
philosophy has been based on the
application of fail-safe design
requirements to the airplane fuel tank
system to preclude ignition sources
from being present in fuel tanks when
component failures, malfunctions, or
lightning encounters occur.
Possible ignition sources that have
been considered include: Electrical arcs, Friction sparks, and Autoignition. (The autoignition
temperature is the temperature at which
the fuel/air mixture will spontaneously
ignite due to heat in the absence of an
ignition source.)
Some events that could produce
sufficient electrical energy to create an
arc include: Lightning, Electrostatic charging, Electromagnetic interference (EMI),
or Failures in airplane systems or
wiring that introduce high-power
electrical energy into the fuel tank
system.
Friction sparks may be caused by
mechanical contact between certain
rotating components in the fuel tank,
such as a steel fuel pump impeller
rubbing on the pump inlet check valve.
Autoignition of fuel vapors may be
caused by failure of components within
the fuel tank, or external components or
systems that cause components or tank
surfaces to reach a high enough
temperature to ignite the fuel vapors in
the fuel tank.
Existing Regulations/Certification
Methods
The current 14 CFR part 25
regulations that are intended to require
designs that preclude the presence of
ignition sources within the airplane fuel
tanks are as follows:
Section