FIGURE 3
Confined Space Placard
12. Ignition Mitigation Means (IMM).
The following are acceptable means to mitigate the effects of an explosion.
a. One means to meet § 25.981 is to protect a tank from structural and systems damage that could prevent continued safe flight and landing of the airplane. This alternative recognizes that an applicant may choose to accept a high flammability exposure in a given tank and to provide additional protection to extinguish or suppress an explosion in a tank if an ignition occurs.
b. The use of appropriate foams to fill the fuel tank and thereby control the pressure rise following an ignition of the fuel vapor/air mixture has been demonstrated to be effective by the United States Air Force (USAF) and other military forces. Foams are in use on several civilian transport category airplane types. Detailed design information regarding use of reticulated polyurethane safety foam for explosion suppression is provided in the report referenced in paragraph 4d(1) of this AC. The applicant may use such a foam installation to satisfy the requirement of § 25.981. The foam type should be demonstrated to be effective in suppressing explosions to a level where structural and system damage is prevented. The applicant should:
(1) Provide data on the foam, including material, pore size, and intended method for installing the foam in the tank.
(2) Address the potential for, and the effects of, degradation of the foam, from any environmental effects and long term aging, on both the airplane and engine fuel systems. If the foam has a limited useful life, particular installation requirements, or other features that are essential for the IMM to perform its intended function, they should be defined as CDCCLs.
(3) Address the effects of the foam installation on fuel system performance, including engine feed, venting, unusable fuel, sump capacity, expansion space capacity, fueling, and defueling, including the effect of the foam on electrostatic buildup in the tank.
(4) Address the effect of the foam installation on the airplane fuel system, as well as the auxiliary power unit (APU) and engine fuel systems, and develop maintenance procedures to ensure the foam is correctly installed, both initially and when reinstalled, if removed for access to the tank.
/s/ Ali Bahrami
Ali Bahrami Manager, Transport Airplane Directorate Aircraft Certification Service 39
Appendix 1 APPENDIX 1 LIST OF § 26.33(a) AFFECTED MODELS/FAA OVERSIGHT OFFICES
TABLE 1-1
Section 26.33(a) Applicable Airplane Models
The following list represents the airplane models determined to meet the applicability criteria of § 26.33(a). This list only represents our best determination at this time and may not be complete. Design approval holders are responsible for identifying all of their airplane models meeting the applicability criteria.
Aerospatiale :
ATR 42, ATR 72 Airbus: A300, A310, A318, A319, A320, A321, A330, A340, A380 BAE: BAe-146, BAe Jetstream 4100, ATP, Avro 146 Boeing: 717, 737, 747, 757, 767, 777, MD-80, MD-90, MD-11 Bombardier: CL-600-2B19 (CRJ-100/200/440), CL-600-2C10 (CRJ-700), CL-600-2D15, CL-600-2D24 (CRJ-900), DHC-8 CASA: CN-235, C-295 Dornier: 328-100, 328-300 Embraer: EMB-120, EMB-135, EMB-145, ERJ-170, ERJ-190 Fokker: F.27 Mk 50, F.28 Mk 0070 and Mk 0100 Saab: 340 (or SF-340), 2000
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Appendix 1
TABLE 1-2
FAA Oversight Offices
Airplane manufacturer FAA Oversight Office Aerospatiale Transport Airplane Directorate, International Branch, ANM-116 Airbus Transport Airplane Directorate, International Branch, ANM-116 BAE Transport Airplane Directorate, International Branch, ANM-116 Boeing Seattle Aircraft Certification Office Bombardier New York Aircraft Certification Office CASA Transport Airplane Directorate, International Branch, ANM-116 deHavilland New York Aircraft Certification Office Dornier Transport Airplane Directorate, International Branch, ANM-116 Embraer Transport Airplane Directorate, International Branch, ANM-116 Fokker Transport Airplane Directorate, International Branch, ANM-116 Lockheed Atlanta Aircraft Certification Office McDonnell-Douglas Los Angeles Aircraft Certification Office SAAB Transport Airplane Directorate, International Branch, ANM-116
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Appendix 2 APPENDIX 2
DEVELOPING CRITICAL DESIGN CONFIGURATION CONTROL
LIMITATIONS - FUEL TANK FLAMMABILITY
1. Introduction. This appendix provides guidance for developing Critical Design Configuration Control Limitations (CDCCL) for fuel tank systems to prevent the fuel tank from exceeding the applicable flammability exposure limits established in the 2008 Fuel Tank Flammability Reduction (FTFR) rule. Guidance for developing CDCCLs to maintain ignition prevention features is located in AC 25.981-1B, Fuel Tank Ignition Source Prevention Guidelines, or the latest revision.
2. Definitions.
a. Aircraft Maintenance Manual (AMM). A manual developed by the manufacturer of a particular airplane that contains information necessary for the continued airworthiness of that airplane.
b. Airworthiness Limitation Item (ALI). Mandatory maintenance of the fuel system that can include CDCCL, inspections, or other procedures determined necessary to ensure, with respect to this AC, the fuel tank flammability exposure does not increase above the certification limits as a result of maintenance actions, repairs, or alterations throughout the operational life of the airplane.
c. Component Maintenance Manual (CMM). A manual developed by a manufacturer that contains information necessary for the continued airworthiness of a particular component.
d. Critical Design Configuration Control Limitations (CDCCL). A limitation requirement to preserve a critical design feature of a flammability reduction system or of the fuel system design that is necessary for the design to meet the performance standards of § 25.981 throughout the life of the airplane model. The purpose of the CDCCL is to provide instructions to retain the critical features during configuration changes that may be caused by alterations, repairs, or maintenance actions.
e. Instructions for Continued Airworthiness (ICA). The information documented in accordance with 14 CFR 25.1529 and 14 CFR part 25, appendix H that includes the applicable methods, inspections, processes, procedures, and airworthiness limitations required to keep the airplane airworthy throughout its operational life.
3. Discussion.
a. Critical Design Configuration Control Li mitations include those features of the design that must be present and maintained to achieve the safety level intended by § 25.981 for the operational life of the airplane. Changes to the airplane, such as installing a fuel re-circulation system, hydraulic heat exchanger in the fuel tank, or a heat source adjacent to the fuel tank, may affect fuel tank flammability exposure. A CDCCL would be necessary in this example to prohibit the addition of heat to the fuel tank.
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Appendix 2 Another example of a CDCCL might be limits on operation with certain fuel types such as JP-4. The CDCCL would also control or prohibit the kinds of modifications to airplanes, like modifications that affect the vent system of a fuel tank that has an FRM installed or the addition of auxiliary fuel tanks that vent into a fuel tank that has an FRM installed, that could adversely change the flammability exposure of fuel tanks to which it may be connected. All fuel tanks subject to the requirements of Amendment 25-125, even those in airplanes that do not have high flammability fuel tanks, will need to have CDCCL defined so that future modifications do not increase the flammability above the regulatory limit. Under part 26, CDCCL must also be provided for fuel tanks required to be modified by FRM or IMM. The application of CDCCL under the FTFR rule is similar to the requirements already applied to fuel tank ignition source prevention in Amendment 25-102 to § 25.981.
b. The FTFR also includes the requirement that visible means identifying CDCCL be present. This is required to prevent alterations to critical features of the system. As the visible identifications are critical to the FRM or IMM system, they are also considered to be CDCCL. Any tampering or removal would be in violation of the CDCCL. These CDCCLs, inspections, or other procedures would be documented as airworthiness limitations in the ICA.
c. The CDCCLs for fuel tank flammability include any information necessary to maintain those design features that have been determined by analysis of the fuel tank system (e.g., fault tree analysis, failure modes and effects analysis) as needed to maintain the performance of the FRM or IMM, or maintain the fuel tank flammability within the limits established by the applicable regulations. AC 25-981-1B (or latest revision) contains additional guidance on how to perform the analysis for ignition prevention CDCCLs. CDCCLs are intended to preclude the occurrence of any maintenance or inspection task or procedure that could result in a failure, malfunction, or defect that would compromise the intended function of the critical part, component or design feature that ensures the fuel tank flammability exposure does not exceed the regulatory limits.
This information is essential to ensure that maintenance, repairs, or alterations do not unintentionally violate the integrity of the original type design of the fuel tank system.
CDCCLs may be required that define the critical features, such as:
• Flammability exposure of the unheated aluminum wing tank, and associated cooling rate,
• Limits on heat input such as adding heat blankets or additional hydraulic heat exchangers,
• Limits on how an auxiliary fuel tank is integrated with an existing airplane fuel tank system, such as limiting venting into a tank with FRM based upon inerting or transferring warm fuel from the auxiliary tank,
• Limits on airplane systems such as minimum quantity of engine bleed air flow or electricity that is required to supply power to an FRM,
• Limits on use of high volatility fuels such as JP-4,
• Quantity of engine bleed air flow that is used for inerting, A2-2
Appendix 2
• Limits on penetrations of the fuel tank,
• Limits on any changes to fuel management that may affect FRM,
• Limits on changes to any placards or means used to visibly identify critical design features of the fuel tank system that must not be compromised for the operational life of the airplane,
• Life limits on parts such as polyurethane foam used as an IMM, and the air separation modules used in an inerting system.
d. Airworthiness limitations are part of the ICA. Design approval holders (DAH) need to make available to affected parties pertinent changes to the ICAs. (The term “make available” is used in the same sense that it is used in § 21.50.) The rule is not intended to alter or interfere with the existing commercial relationships between TC holders and these other persons. The FAA anticipates that DAHs would be able to be reasonably compensated for developing these documents, as they are under current practice.
e. The rule requires creation of an Airworthiness Limitations Section (ALS), unless previously established. The ALS is required by current part 25 and includes those items that have mandatory inspection or replacement times related to fuel systems and structure. The ALS is included in the ICA, approved as part of type certification, and distributed with an airplane on delivery. In this way the ALS is visible to all who need it and who would be required to comply with it under §§ 121.917, 125.509 and 129.117.
For those airplanes that currently do not have an ALS, the rule requires an ALS only for fuel tank safety related limits. This rule does not require that the ALS for these airplanes include the other requirements for an ALS established under Amendment 25-54 to part 25, or a later amendment. For those DAH or applicants with airplanes certified to Amendment 25-54 or later, the existing ALS would be revised to include the fuel tank system ALI.
f. The ICA developed by the DAH using the guidance in this advisory circular must be approved by the responsible FAA Oversight Office. Those approved instructions are required by related operational rules to be used by operators to develop and propose changes in their maintenance programs and incorporate design changes needed to maintain the fuel tank flammability within the approved limits and to ensure continued airworthiness of certain features of the FRM and IMM for the operational life of the airplane. These changes to the maintenance programs must be reviewed and approved by the operator’s designated FAA inspector or Principal Inspector.
4. Development of Critical Design C onfiguration Control Limitations.
a. The CDCCLs, which are a type of Airworthiness Limitation, are the primary means of managing and controlling the configuration of the FRM, IMM or design features that affect the flammability of any fuel tank that does not require an FRM or IMM. In the context of this AC, CDCCLs provide limitation requirements for configuration management to preserve the integrity of certain critical flammability features of the fuel tank system design. These critical features are essential to ensure fuel A2-3
Appendix 2 tank flammability does not increase above limits defined in the regulations as a result of configuration changes caused by maintenance action, repair, or alteration of those critical features. While initial inspections may be necessary to ensure that a CDCCL has not been compromised (e.g., because of aging, wear, maintenance, alterations, etc.), they are not intended to require repetitive inspections. Rather the intent of the CDCCL is to ensure that all affected maintenance personnel are aware of the need to make sure the configuration identified by the CDCCL is preserved for the operational life of the airplane.
b. The DAH may determine that the CDCCLs are applicable at the individual part level or at the component level. In the context of this guidance, components are assembled from parts. Design approval holders may elect to identify a CDCCL that applies to the component for the purposes of reducing tracking of ALIs that may apply to individual parts of the component. If the component level is used, the design approval holder is responsible for revising the CMM instructions to identify all of the critical features of the component design for approval by the FAA Oversight Office.
c. To identify the parts or components to which the CDCCLs are applicable, the DAH must first conduct a configuration assessment of the fuel tank system design. The purpose is to identify any foreseeable maintenance or inspection actions or other causes that could compromise the configuration of a critical feature of the fuel tank system. In the context of this guidance, foreseeable causes are those that have occurred in service in the past or those that engineering judgment predicts could compromise the critical feature of a part or component of a fuel tank system. The DAH must develop maintenance and inspection instructions to prevent those foreseeable changes to the design configuration of the critical ignition source prevention features.
d. Airworthiness Limitations Section Content. The ALIs should include the following:
• The Limitation Statements shown below,
• A brief description of the flammability reduction, ignition mitigation means features,
• The flammability issue associated with inadvertent changes to the configuration of each of those design features, and
• The reference to maintenance instructions, if applicable, and other information in manuals (such as airplane maintenance, standard wire practices manual, etc.,) that have been revised or created to advise affected personnel of the CDCCLs.
e. Limitation Statement: The Critical Design Configuration Control Limitation statements are as follows:
A2-4
Appendix 2 LIMITATIONS.
(1) The critical features of the parts or components identified in the CDCCLs must be maintained in a configuration identical to an approved type design for the airplane.
(2) Any repairs or overhauls to the critical features of the parts or components that are identified must be maintained in accordance with the design approval holder’s maintenance manual or with other acceptable repair or overhaul specifications and parts approved by the FAA Oversight Office specifically for that part or component.
(3) In cases where the critical features of a component are specified, any test equipment or tooling utilized to repair or overhaul the component must be in accordance with the CMM or otherwise comply with 14 CFR 43.13(a) and be substantiated and documented as equivalent.
5. Identification and Awareness of CDCCLs.
a. The DAH should list the parts components or features to which the CDCCLs are applicable for a particular airplane in the service information (e.g., maintenance planning document or special certification item document) documenting the CDCCL. This is the mechanism for identifying critical features and requiring their control. To ensure that the operator introducing a modification or the mechanic is aware of the need to consider these critical features, it will be necessary to insert cross-references in certain documents to comply with the CDCCLs.
(1) The DAH should identify a task with WARNING or CAUTION notes for a component or part that has a critical design feature in the AMM. The operator should incorporate acceptable procedures to ensure compliance with the CDCCLs.
(2) The DAH should include information in standard practices manuals to ensure the CDCCL information is provided to those making modifications or maintaining the type design. (see AC 25-26, Development of Standard Wiring Practices Documentation (11/14/07) for guidance on preparation of these manuals).
(3) The DAH should identify the appropriate CMM. In addition, the design approval holder should ensure that a statement is inserted into both the CMM and the Airplane Maintenance Manual that the component is controlled by the CDCCL and, therefore, that it may be repaired or overhauled only in accordance with the CMM or other acceptable maintenance procedures and parts approved by the FAA Aircraft Certification Office.
(4) These documents should include a statement that the part, component or design feature component is controlled by the CDCCL and, therefore, that it may be A2-5
Appendix 2 repaired or overhauled only in accordance with the CMM or other acceptable maintenance procedures approved by the FAA Oversight Office.
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Appendix 3 APPENDIX 3 COMPLIANCE WITH PART 26, SUBPART D, SECTIONS 26.33 AND 26.35
1. Section 26.33 Holders of type certificates: Fuel tank flammability. This section requires TC holders of certain large transport category airplanes described below to analyze the flammability exposure of all their affected airplanes’ fuel tanks and develop service instructions for those tanks that exceed limits defined in the rule. For example, a TC holder of an affected airplane with any fuel tank that is determined by the analysis to have high flammability exposure (over 7 percent) is required to develop service instructions for IMM or FRM to reduce the flammability exposure of the fuel tank. If the fuel tank is normally emptied and any portion of the fuel tank is located within the fuselage contour, § 26.33(c)(1)(i) requires the FRM meet the flammability exposure criteria of appendix M of part 25. For all other fuel tanks with a flammability exposure over 7 percent, § 26.33(c)(1)(ii) requires the FRM meet the flammability criteria of appendix M except instead of complying with paragraph M25.1 of the appendix the fleet average flammability exposure may not exceed 7 percent. The affected TC holders would also be required to submit compliance plans for the flammability analysis and the development of service instructions for an FRM or IMM. The due dates for items required by this regulation are as follows:
Rule effective 9/19/08 Compliance plan for flam.
analysis 12/18/08 Flam.
analysis completed 2/16/09 Compliance plan for design change and service instructions 4/17/09
FRM/IMM service instructions, ICAs, ALS 9/20/10 Draft of compliance items 7/22/10 90 days 60 days 60 days 15 months 60 days
FIGURE 3-1
Compliance Timeline for TC Holders (§ 26.33) A3-1