DEC-21-2010 14:25 Fflfl RENTON P.02/07 

Exemption No. 10175 

UNITED STATES OF AMERICA 

DEPARTMENT OF TRANSPORTATION 

FEDERAL AVIATION ADMINISTRATION 

RENTON, WASHINGTON 98057-3356 

• — 5 

'D 

U J 

— 

p=v>:;c:< 

•Tl^"- ^ 

q-.^F^ 

—i—Zr Pi^ 

CO 

UAJ 

In the matter of the petition of 

Bombardier Aerospace 

for an exemption from § 25.981(a)(3) of Title 

14, Code of Federal Regulations 

Regulatory Docket No. FAA-2010-0287 

GRANT OF EXEMPTION 

By letter dated February 25,2010, and additional information dated May 14,2010, Mr. C. Nham, 

Senior Project Manager, Fixed Wing Large Transport Aircraft, National Aircraft Certification, 

Civil Aviation, Transport Canada, Aircraft Certification Branch (AARDE), 3'*' Floor, Tower C, 

Place De Ville, 300 Sparks Street, Ottawa, Ontario, Canada Kl A 0N8, petitioned the FAA, on 

behalf of Bombardier Aerospace, for a partial exemption from the requirements of § 25.981(a)(3) 

of Title 14, Code of Federal Regulations (14 CFR). This exemption, if granted, would permit 

relief from the fault tolerance ftiel tank ignition prevention reqxiirements for its Model CL-600-

2E 25 (CRJ 1000) series airplanes allowing them to (1) demonstrate that the structural design 

provides two independent, effective and reliable means of lightning strike protection, and (2) 

demonstrate compliance with this requirement by 24 months after type certification of the 

airplane. 

The petitioner requests relief from the following regulation: 

Section 25.981(a)(3) as amended by Amendment 25-102: 

(a) No ignition source may be present at each point in the fiiel tank or fuel tank system 

wiiere catastrophic failure could occur due to ignition of fuel or vapors. This must be 

shown by: 

(3) Demonstrating that an ignition source could not result from each single failure, from 

each single failure in combination with each latent failure condition not shown to be 
DEC-21-2010 14:25 FRfl RENTON P.03/07 

extremely remote, and from all combinations of failures not shown to be extremely 

improbable. The effects of manufacturing variability, aging, wear, corrosion, and likely 

damage must be considered. 

The petitioner supports its request with the following information: 

This section quotes, in part, the relevant information from the petitioner's documentation. The 

complete documentation is available at the Department of Transportation's Federal Docket 

Management System, on the Internet at http://regulations.gov, in Docket No. FAA-2010-0287. 

As explained in FAA policy memo ANM-112-08-002, before amendment 25-102, the 

concept of lightning protection of the fiiel tanks was normally applied in preventing 

ignition of vapors in the tank area. There was no consideration of design failures, aging, 

wear or maintenance induced errors to the fiiel tank structure. As a result, the FAA 

policy now specifies that compliance with 14 CFR Part 25.981(a)(3) would typically 

require a design with three highly reUable, independent and redimdant protective features 

to prevent ignition in the event of a lightning strike. The structural elements of the wing 

tank design of the Bombardier Aerospace (BA) CL-600-2E25 (CRJIOOO) do not comply 

with this requirement. 

It was noted in the policy memo that the FAA determined that in certain cases it was in 

the public interest to grant an exemption for structural related elements provided that 

certain conditions are met ensuring an acceptable level of safety. In view of this 

allowance, BA is applying for a two-part exemption for the structural elements of the fuel 

tank design. Firstly, to demonstrate that the design complies with the requirement ever 

with only two independent, effective and rehable means of lightning strike protection. 

Secondly, that the demonstration of compliance to this requirement be made after type 

certification of the CRJIOOO. 

BA has implemented a compliance plan to meet the requirements of the FAA policy in 

support of this exemption application, however, it has been concluded that the analyses/ 

assessments, compilation and documentation of the substantiating data cannot be 

completed in time for CRJIOOO type certification on the basis that some of the test data 

required to show compliance would not be available prior to this date. A schedule has 

been included as part of this compliance plan outlining the milestones towards the 

completion of this deliverable by the middle of September 2012. 

Fuel tank ignition prevention is ensured through low fuel tank flammability exposure and 

the preclusion of ignition sources within the tank. The prevention of ignition soiirces is 

substantiated by analysis of all potential ignition sources, using the guidance of AC 

25.981-1B (noting that this AC did not address the "structural lightning" aspects) and the 

development of airworthiness limitations, both fiael system mandatory inspections and by 

defining critical design configuration control limitations (CDCCLs). As added safety 

justification, design changes required to show compliance with SCA H2002-03 have been 
DEC-21-2010 14:25 FRfl RENTON P.04/07 

accomplished. All the resulting mandatory modifications are included as an integral part 

of the CRJIOOO type design. Low ftiel tank flanunability exposure has been demonstrated 

for FAR 26.33 compliance as per FAA guidance AC 25.981-2A and Pan 25, 

Appendix N. 

BA considers the design of the CRJIOOO wing a safe design, witii good service history 

and meets authority expectations for an aluminum wing design. BA believes granting this 

exemption has no impact on safety. 

Federal Register YnbMcation 

A simimaiy of the petition was published in the Federal Register on September 20, 2010 (75 FR 

57328). No comments were received. 

The FAA's analysis 

In May 2001, the FAA issued the "Transport Airplane Fuel Tank System Design Review, 

Flammability Reduction, and Maintenance & Inspection Requirements" final rule (Docket 

FAA-l 999-6411, effective Jime 6,2001) tiiat vras adopted as Amendment 25-102. This 

amendment added specific ignition prevention requirements and a new flammability 

minimization requirement to § 25.981. 

The amended ignition prevention requirements in § 25.981(a)(3) require consideration of factors 

such as aging, wear, and maintenance errors as well as the existence of single failures, 

combinations of failures, and latent failures that may be the cause of ignition sources in fuel 

tanks. 

Section 25.981, as amended by Amendment 25-102, requires that airplane designs be protected 

from the effects of structural lightning with feamres that are failure tolerant. Prior to this 

amendment, only § 25.954 had been apphed to lightning protection of fuel tanks. That provision 

requires only that the airplane design prevents ignition of vapors in the tank with no 

consideration for anticipated design failures, aging, and wear, or maintenance errors. 

Systems with potentially catastrophic failure modes would typically meet the requirements of 

§ 25.981(a)(3) by providing at least triple redundancy in their protective features with periodic 

inspections, or dual redundant features v^ith continuous system monitoring to reduce the latency 

period. Dual redundant design schemes could only comply with § 25.981(a)(3) when combined 

with either regular inspections at very short intervals or a monitoring device to verify the 

fimctionality of the protective features. Inspection of the various design features may be difficult 

or impossible if the feature is internal to the fiiel tank and part of the wing structure. 

When § 25.981 was applied to the structural Ughtning aspects of new airplane designs, applicants 

foimd it was impractical to meet the standard and incorporate additional protective features. We 
DEC-21-2010 14:25 Fflfl RENTON P.05/07 

issued two exemptions and developed new policy. The two exemptions were for the Dassault 

Falcon IX, signed on April 20, 2007, and the other was for the Hawker 4000, signed on August 

28,2008. On May 26,2009, following a public-comment period, we adopted new policy that 

defined criteria that we would consider regarding granting of exemptions and issuance of special 

conditions for structural lightning protection. 

As discussed in the preamble to Amendment 25-102, conventional, unheated, aluminum wing 

tanks minimize fiiel tank flammability exposure, as required by § 25.981(c). Even if a latent 

failure of a protective feature occurred for such a tank, the risk of lightning induced fiiel tank 

explosions is relatively low when the tank is fueled with low volatility fuels such as Jet A, as 

demonstrated by the service experience of these tanks. Because of the impracticality of ftill 

compliance with §25.981 (a)(3) for lightning protection and the reduced flammability exposure 

of these tanks, we beheve granting an exemption is in the public interest if applicants can show 

that their design provides practical dual protective features for fiiel-tank structural lightning 

protection that are both independent and robust, and show the probability of fiiel tank ignition to 

be extreniely improbable for any non-fault-tolerant features. 

Bombardier provided initial data in support of their exemption request that shows, pending the 

results of testing and additional analysis, their design should meet the criteria of the FAA policy. 

Bombardier's request for an exemption states they will demonstrate that the structural design 

provides two independent, effective and reliable means of lightning strike protection. Such fault 

tolerant features may be practical for fasteners. However, similar designs have included single 

failures of structure that could result in a fuel tank ignition source during certain lightning strike 

events. As stated above, FAA policy allows for accepting single failures when certain criteria in 

the policy memo have been met. This includes demonstrating the probability of fuel tank 

ignition to be extremely improbable for any such non-fault-tolerant features. We anticipate after 

fiirther analysis Bombardier may identify such single failures in the design of the CL-600-2E25 

(CRJ 1000). If single failures exist in the design, Bombardier would need to modify their 

exemption request to expand the scope to include single failures as provided for in this policy 

and summarized below:. 

Fault tolerance is not required for any specific design feature if: 

a. providing fault tolerance is shown to be impractical for that feature, and 

b. fiiel tank vapor ignition because of that feature and all other non-fault-tolerant 

features, when their fiiel tank vapor ignition event probabiUties are summed, is shown 

to be extremely improbable. 
DEC-21-2010 14:25 Fflfl RENTON P.0&/07 

On November 2, 2010, Transport Canada Civil Aviation (TCCA) issued an exemption allowing 

Bombardier, until October 29,2012, to complete die necessary certification testing, mitigation, 

analysis and documentation to show the CL-600-2E25 (CRJ 1000) complies with the TCCA 

certification requirements for structural Ughtning protection under AWM 525.981(a)(3). That 

same data will be used to show die CL-600-2E25 (CRJ 1000) does meet the FAA sft-uctural 

lightning policy. 

The CL-600-2E25 (CRJ 1000) airplane type certification program is near completion. Witiiout 

this exemption. Bombardier would not receive FAA design approval for the aircraft in a timely 

maimer, putting it at an unfair disadvantage with its competitors. This could also cause disruption 

to several major corporations in the world that are anticipating the imminent delivery of the CL600-2E25 (CRJ 1000) airplane to ineet their business needs. These Bombardier customers may 

need to find alternatives for their aviation needs if this exemption is hot granted. We further note 

that Bombardier has indicated that no U.S. operators have placed orders for the CL-600-2E25 

(CRJ 1000) airplane. 

The FAA's Decision 

In consideration of the foregoing, I find that a grant of exemption is in the public interest. 

Therefore, pursuant to the authority contained in 49 U.S.C. §§ 40113 and 44701, delegated to me 

by the Administrator, Bombardier is hereby granted an exemption from the requirements of 14 

CFR § 25.981(a)(3) as it relates Model CL-600-2E25 (CRJ 1000) series airplane fiiel-tank 

structural lightning protection with the following provisions: 

1. Instead of compliance with the requirements of § 25.981 (a)(3). Bombardier must show 

that the design includes at least two independent, effective, and reliable lightning 

protection features (or sets of features) such that fault tolerance to prevent lightningrelated ignition sources is provided for each area of the structural design that they have 

shovm and FAA has determined to be impractical for fiill compliance. 

a. Bombardier must identify all features that meet this two-layer protection 

provision and all features that do not include two-layers.. 

b. If any features do not meet this two-layer protection provision. Bombardier 

must petition to expand this exemption to include the non-fault tolerant 

provision described in FAA PoUcy Memorandum ANM-112-08-002, Policy 

on Issuance of Special Conditions and Exemptions Related to Lightning 

Protection of Fuel Tank Structure, dated May 26, 2009. 

2. Bombardier must perform an analysis to show that the design, manufacturing processes, 

and airworthiness limitations section of the instructions for continued airworthiness 

include all practical measures to prevent, and detect and correct, failures of structural 

lightning protection features because of manufacturing variability, aging, wear, corrosion, 

and likely damage. 
DEC-21-2010 14:26 Fflfl RENTON P.07/07 

3. Bombardier must demonstrate compliance with provisions 1 and 2 of this exemption 

within 24 months after type certification of the airplane. 

4. If Bombardier is unable to demonstrate compliance with provisions 1 and 2- of this 

exemption within 24 months after type certification of the airplane, the FAA will not 

issue further airworthiness certificates until Bombardier shows that the conditions are 

met. 

Issued in Renton, Washington, on DEC 1 4 2010 

Michael J. Kaszycki 

Acting Manager, Transport Airplane Directorate 

Aircraft Certification Service 

TOTflL P.07