OVERVIEW

Background

The Federal Aviation Administration (FAA) recently released policy memo ANM-112- 08-002 on the fuel tank safety provisions of Title 14, Code of Federal Regulations (14 CFR) 25.981(a)(3), as amended by Amendment 25-102, for lightning protection of fuel tank structure. The FAA developed this policy because they determined that compliance with current regulatory standards applicable to lightning protection of fuel tank structure may be impractical in some cases for some areas of structural design.

This document is intended to provide guidance to manufacturers who may apply this policy to their type design programs and to establish criteria to encourage a consistent approach be applied across industry. The content of this document has been developed by the SAE AE-2 and EUROCAE WG-31 lightning committees. Manufacturers should coordinate directly with their certifying authority to ensure that their proposed application of this policy is acceptable and the means of compliance and compliance data planned are sufficient for certification.

Process Overview

Application of the policy has been broken down into a number of process steps in this document. Figure 1.2-1 provides an overview of the high level process to apply the policy. This process consists of the following major steps:

a) Section 1.3 describes the initial assessment required to determine eligibility to apply the policy.

b) Figure 2.0-1 provides a process flowchart for determining the regulatory path based on the options described in the policy. The three main options are direct compliance with § 25.981(a)(3), special conditions as defined in the policy or petitioning for an exemption using the criteria defined in the policy. The latter two options are dependent upon the level of flammability exposure in the design. Detailed process steps are provided in Section 2.

c) Figure 3.0-1 provides a process flowchart for how to assess the design for fault tolerance. Detailed process steps are provided in Section 3.

d) For areas of the design where it is found to be impractical to provide fault tolerance, Figure 4.0-1 provides a process flowchart for how to conduct the required numerical probability assessment to ensure a fuel vapor ignition is extremely improbable. The detailed process steps associated with this are described in Section 4.

e) Figure 5.0-1 provides a process flowchart for how to verify compliance of the protection design. This will typically include verification of fault tolerance by test. Detailed process steps are provided in Section 5.

f) Section 6 describes a step that addresses the analysis required to demonstrate that all practical measures have been incorporated into the design, manufacturing processes and instructions for continued airworthiness to prevent, detect and correct failures of structural lightning protection features.