U.S. Deparrment
oflronsportomn
Federal Aviotion
Administration
Advisory
Circular
s”bjecf’ PROTECTION OF AIRPLANE FUEL
SYSTEMS AGAINST
FUEL VAPOR
IGNITION DUE TO LIGHTNING
Ihk: 4/ 12185
Initialed by: ACE-100
AC
No:
20-53~
ChPngC:
1.
PURPOSE.
This Advisory Circular (AC) provides information and guidance con-
cerning an acceptable means, but not the only means, of compliance with Parts 23
or 25 of the Federal Aviation Regulations (FAR), applicable to preventing igni-
tion of fuel vapors due to lightning. Accordingly, this material is neither man-
datory
nor
regulatory
in
nature and does not constitute a regulation.
In lieu of
following this me:hod, the applicant may elect to establish an alternate method
of compliance that is acceptable to the FAA for complying with the requirements
of Section 23.954 and 25.954.
2. SCOPE.
This Advisory Circular provides guidance for a means of showing
compliance with regulations for protection against lightning fuel vapor ignition
hazards to airplane fuel systems of conventional design
as
well as for those
involving advanced composite structures or other new technologies. The document
incorporates information and references related to improvements in the state-of-
the-art, with respect to lightning effects and verification methods that have
taken place since the previous version of this Advisory Circular was published.
Ignition hazards addressed include those due to direct effects (on fuel tank
structure/components and plumbing) as well as indirect effects on wires or cir-
cuits
in a fuel vapor cavity (such as fuel quantity probes),
Guidance in this
document applies to fuel tanks and systems which are a part of the structure of
an airplane, as well as externally mounted tanks on wing tips, fuselage, or
other
parts of the airplane. This guidance applies to
systems
included in
the
initial
design
as
well as modifications,
such
as additional tanks or other fuel system
components. Since externally mounted tanks are often located in direct lightning
strike zones,
they
may be especially vulnerable to lightning hazards if not ade-
quately protected.
NOTE:
This advisory circular does not address the indirect induced
effects
(upset or damage) on either
analog or digital electronic or
electrical systems, except as they relate to fuel ignition hazards.
3. CANCELLATION.
Advisory Circular No. 20-53, .effective October 6, 1967.
4. RELATED FAR SECTIONS.
Part 23, section 23.954, and Part 25, section 25.954.
5.
RELATED READING MATERIAL.
A comprehensive
discussion
on this subject, with
additional nonregulatory guidance information, is available in the following
; document:
-i
Users Manual for AC20-53A,
Fuel Vapor Ignition Due
to
Lightning,”
“Protection of Airplane Fuel System Against
Report
Number
DOT/FAA/CT-8313. This docu-
ment is available to the public by order
through
the National Technical
Information Service, Springfield, Virginia 22161.
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