FAA AC 20-53A PDF

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 circuits 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 adequately 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.

PURPOSE.

This Advisory Circular (AC) provides information and guidance concerning an acceptable means, but not the only means, of compliance with Parts 23 or 25 of the Federal Aviation Regulations (FAR), applicable to preventing ignition of fuel vapors due to lightning. Accordingly, this material is neither mandatory nor regulatory in nature and does not constitute a regulation. In lieu of following this method, 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.