B

Nov 19, 2012 

AW-CRJ/12/746

Mr. Ali Bahrami 

Federal Aviation Administration (FAA) 

Manager (TAD) 

New York Aircraft Certification Office, ANE-171 

1600 Stewart Avenue, Suite 410 

Westbury, NY 11590

 

Subject: CL-600-2E25 (CRJ1000) Exemption Request Against 14 CFR Part 

25.981(a)(3) 

Reference: 

1. FAA exemption no 10175 against 14 CFR Part 25.981(a)(3) dated 

 Dec 17, 2010 

2. TCCA Issue Paper AV-1 edition 3 (closed) dated Oct 26, 2010 

3. Revised Exemption request application form against AWM 

 525.981(a)(3); – see attachment 1; 

4. Compliance plan (including revised Project Plan schedule) for 

 AWM 525.981(a)(3) – see attachment 2; 

5. EMC TDS-698-28-BA-2028 revision A 

6. Electro Magnetic Compatibility (EMC) memo CRJ900-01-66-2012- 

 33 dated Oct 12, 2012 – see attachment 3 

7. Fuel systems memo CRJ1000/28/2010/001/EH dated Mar 29, 

 2010 – see attachment 4 

8. Reliability, Maintainability & Safety (RMAS) memo dated Mar 29, 

 2010 – see attachment NCR #061-2012 dated 29 Oct 2012 

9. FAA FAA Policy memo ANM-112-08-002 dated May 26, 2009 

 

Dear Mr. Bahrami, 

The purpose of this letter is to request for an extension to the compliance date for the 

currently published exemption 10175 (reference item 1) against FAA requirement 14 

CFR Part 25.981(a)(3) subject to FAA Policy memo ANM-112-08-002 (ref item 9). It 

should be noted that FAA exemption 10175 allows the CL-600-2E25 aircraft to be 

certificated for a limited period of time without having shown compliance to FAA Policy 

memo ANM-112-08-002. The time period for such an allowance expires on Dec 17, 

AEROSPACE

Bombardier Inc. 

P.O. Box 6087, Station Centre-ville 

Montréal, Québec, Canada H3C 3G9 

Telephone 1(514) 855-5000 

Fax 1(450) 476-7361 

www.bombardier.com 

3 

Attachment 1 to BA letter AW-CRJ/12/746 dated November 19, 2012 

EXEMPTION REQUEST APPLICATION FORM

Request made by: Bombardier Inc. 

 400 Cote-Vertu Road West 

 Dorval, Quebec, Canada 

 H4S 1Y9 

Request made to: Federal Aviation Administration (FAA) 

Date request made: 19 Nov 2012 via letter AW-CRJ/12/746

Regulatory standard(s): 14 CFR Part 25.981(a)(3) “Fuel Tank Explosion 

Prevention” at amendment 25-102 

 

1- Requirement text: 

14 CFR Part 25.981(a)(3) states: 

 

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

where catastrophic failure could occur due to ignition of fuel or vapours. This shall be 

demonstrated 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 

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 shall be considered.” 

2- Reason for exemption request:

The reason for this exemption request is to petition for a revision to the currently 

published exemption 10175 against FAA requirement 14 CFR Part 25.981(a)(3) as full 

compliance will not be demonstrated prior to Dec 17, 2012. In TCCA Issue Paper AV-1, 

BA had agreed that the demonstration of compliance with AWM 525.981(a)(3) 

(Amendment 525-12), required substantiation by dedicated tests to ensure that the 

structural aspects of the CL-600-2E25 fuel tank design feature two independent, 

effective and reliable means of lightning protection. As well, BA needs to demonstrate 

full compliance for the fuel system aspects. BA plans to utilize TCCA Issue Paper AV-1 

as acceptable means of compliance with 14 CFR Part 25.981(a)(3) per the guidance of 

FAA Policy memo ANM-112-08-002. 

The results of these tests were positive but did not fully conclude that all elements of the 

structure demonstrated compliance with this requirement. Due to some incomplete 

coupon testing and test coupon failures, BA needs to conduct additional testing/analysis 
4 

and therefore proposes a revision to the compliance plan (see attachment 2) and the 

compliance date as it will no longer be achieved. This new compliance plan provides the 

BA position as to how compliance will be fully achieved within the areas of concern. It 

should be noted however that significant progress has been made to date based on the 

testing that has been accomplished. Compliance could currently be shown for the 

system aspects (as documented in RBR-BA698-144) and the majority of the structural 

aspects. This petition is only required due to those limited areas of the fuel tank 

structure where full compliance cannot currently be demonstrated. 

A schedule has been included as part of this compliance plan outlining the milestones 

towards the completion of this deliverable by Dec 17, 2015 (see attachment 3). As the 

areas of concern will result in design changes to the CRJ1000, this now creates a new 

scenario where originally it was anticipated that no design changes would be necessary. 

Hence, this is why the Dec 17, 2015 date is being proposed to allow us the time to 

facilitate this activity. A number of factors contribute to the 3 yr extension time and why 

any lesser time would be of high risk. Some of these risk factors include the following: 

 Test campaign of the redesign may not be successful as there are aspects of the 

design for which it may not be possible to provide an apparent means of 

protection. 

 Uncertainty and/or lack of confidence in the upcoming proposed redesign option 

may result in additional investigations for alternate design solutions (such as 

other suppliers, etc) which require some buffer in the schedule for potential 

delays. 

 No testing is currently planned to support the safety analysis. If such testing is 

necessary (for example if the planned redesign testing fails) the timeframe to 

produce additional test articles, test, and prepare the safety analysis is very 

short. 

3- Means of Compliance

Fuel systems: 

See attachment 2 for the detailed compliance plan. Fuel system elements and related 

components of the wing fuel tank design, full compliance has been demonstrated and 

documented in BA Fuel Tank System Safety – Ignition Prevention Report, RBR-BA690-

144, as part of the CL-600-2E25 type certification activities. The details of this plan are 

outlined in the attached BA Fuel System internal memorandum 

CRJ1000/28/2010/001/EH dated Mar 29, 2010 (Attachment 4). 

Structure:

For the fuel tank structure-related design elements, compliance will be demonstrated as 

follows: 

 For certain areas of the wing fuel tank structure, the design includes at least two 

independent, effective and reliable means of protection such that fault tolerance 

is provided for each area of the design; 

 For areas of the design where it is deemed impractical or where fault tolerance 

cannot be established, BA will present a risk analysis and/or test data where it 

will be shown that fuel tank vapor ignition is extremely improbable. 
5 

See attachment 2 for detailed compliance plan addressing the above two items. EMC 

memo CRJ900-01-66-2012-33 dated Oct 12, 2012 (see attachment 3), outlines the EMC 

plan to complete the activities required to demonstrate full compliance for design 

features which did not pass the previously completed testing. BA commits to complete 

this exercise by Dec 17, 2015, as stated in this memo and associated schedule. Note, 

this covers the worst case scenario where it may reveal via further analysis & testing that 

the result of the non-compliance requires a design change to the aircraft. Hence this 

date is based on the worst case scenario. 

Once all the test data are formally documented, BA will update report RAZ-BA698-017 

“CL-600-2E25 Wing Tank Structural Survey in Support of Compliance with AWM 525-14 

CFR 25.981(a)(3)” (at the next applicable revision), and formally submit to TCCA for 

review and acceptance. Recall this RAZ report provides the methodology on how 

structural failures modes were discovered and later classified as potential ignition 

sources. This next update will ensure that all test results are properly document and 

compliance has been ultimately demonstrated. 

The RMAS memo (Attachment 4) outlines the procedures for a safety assessment of the 

non-fault tolerant items identified in phase 2 of this project. Some of the work required 

for this phase of the project is dependent upon data that will only be made available in 

the commitment shown in Attachment 3. 

. 

4- Compensating factors (Effect on safety)

To facilitate this time-limited exemption request revision to 10175, BA is offering the 

following substantiation showing that the current design is safe, in order to justify 

allowing BA sufficient time after the current exemption deadline date (i.e. Dec 17, 2012) 

to complete the tasks as noted in the above attachments. 

4.1 – Protection features

4.1.1- Fasteners

The CRJ1000 wing box overall design concepts are identical to those of the 

CRJ700/900. The upper and lower fuel tank skins are made from aluminum alloy planks 

with integrally machined stringers spliced together. Fasteners at splices, rib/plank and 

spar/plank interfaces are of the “Hi-Lite” type, which are installed interference fit. The 

structural integrity of these design features for the CRJ700 and CRJ900 airplane models 

are currently being proven during full scale fatigue testing. The CRJ700 has been cycled 

for full life (i.e. reaching its target of 160,000 flights) with no anomalies noted. The 

CRJ900 test articles have so far successfully accumulated more than 155,000 flights 

with a target of 160,000 flights. No issues have been reported. 

Bombardier Aerospace Process Specification (BAPS) 151-029 “Installation of Hi-Lite 

Fasteners”, rigorously controls the installation of the fasteners. BAPS 151-029 specifies 

many acceptance criteria against which the fastener installation is checked. These 

criteria include the specification of holes as well as installation. Some examples of these 

criteria are hole diameter, hole/countersink angularity, pin protrusion limits, torquing, 

flushness and visual inspection for cracked nuts. Any failure to meet the acceptance 

criteria shall be cause for rejection. 
6 

In addition, all fasteners that penetrate the fuel tank are installed wet as per BAPS 157-

027, to preclude leakage and corrosion. 

4.1.2 - Prior testing done on the early Challenger variants

As part of the original Challenger (CL-600-1A11) certification effort, zone 2A direct 

lightning strike tests were carried out on four fuel tank skin splice coupons. The coupons 

were constructed using the same types of materials and processes as are used for 

production airplanes. All coupons used representative fasteners that were installed 

using the same pitch as on the airplane. Both faying surface seals and fillet seals were 

used to make the test articles production representative. The fasteners were wet 

installed; however, there was no brush sealant over the fastener ends in order to 

facilitate hot spot detection. 

The tests included strikes to both the skin and the fastener heads. No sparking or hot 

spots were detected. The test results are documented in BA report RAE-600-110, “CL600 Design Compliance Aircraft Lightning Protection”. 

4.1.3 - Consideration of single point failure of the fastener

When considering the robustness of our fastener design and installation, BA assures 

continuity of the fastener throughout the aircraft life and that there is no possibility of 

installation or Q.A. perturbations that could result in a fastener mis-installation or failure. 

Furthermore, it should be noted that there has been no reported events of in-service 

fastener cracking, or any other scenario that could lead to arcing (since fastener 

continuity is maintained as supported by fatigue testing). This is in consideration of the 

types of fasteners used, the controlling specifications, Q.A. requirements, thickness of 

fastened components, size and fastener material details, interference fit provided and 

historical data, which demonstrates the effectiveness of our design. 

4.1.4 - Sealant

Application of sealant to the fasteners is a common method of preventing fuel leaks and 

is also used to aid in the prevention of an ignition source in the fuel tank during a 

lightning strike. According to ‘Lightning Protection of Aircraft’ (Fisher, F.A., and Plumer, 

J.A.), “the sealant acts to contain the arcs and sparks which occur at these fasteners 

during a strike attachment and prevents contact of the arc products with the fuel vapor 

space.” 

As previously mentioned, all fasteners that penetrate the CRJ700/900/1000 fuel tanks 

are wet installed. An additional brushed seal (dome sealant) is applied to the interior 

end of the fastener. The application of this brushed sealant is rigorously controlled by 

BAPS 157-027 “Integral Fuel Tank Sealing”. A Quality Assurance process is in place to 

ensure that all the requirements from this BAPS are met. 

In addition, the BAPS requires that the fuel tank sealant be leak tested per the applicable 

Functional Test Procedure. In order to meet the intent of the BAPS and 25.981(a)(3), a 

complete wing reservoir pressure leak test is performed on every aircraft during 

production, per FTER-IN670-281102. This test consists of pressurizing the complete 

main wing reservoirs to 3.5 psi, including the collector bays and center reservoir for 60 

minutes, to ensure no evidence of leakage. 
7 

During the SFAR 88 campaign to improve fuel system safety, BA conducted inspections 

of CRJ fuel tanks on in-service aircraft. It was noted that even after many years of 

service experience, there has been no known instance of sealant deterioration. 

BA has previously presented to TCCA the use of sealant as a means of containing arcs 

and sparks in order to avoid having an ignition source within the fuel tank. The fuel 

access panels are attached to the wing by screws (which are non-interference fit) that 

pass through a clamping ring, pass through the access panel and are held by dome 

anchor nuts that are attached with rivets to the access panel (see Figure 1). During 

zone 2A testing of the original Challenger fuel access doors, it was found that sparking 

occurred at the interface of the dome anchor nuts and the rivets used to retain the dome 

anchor nuts. Pictures of the sparking were recorded. The test was re-done with a new 

panel where the countersink holes in the retaining ring were prepared with alodine and 

the dome anchor nuts and retaining rivets were potted with sealant. There was no 

evidence of sparking or arcing during the retest. This is presented in RAE-600-110 “CL600 Design Compliance Aircraft Lightning Protection”. This report also contains other 

examples, such as the secondary feed fuel pump where sealant was used as a means 

to suppress sparking at the pump retaining fasteners and anchor nuts and rivets of the 

pump box. 

The test described above can be seen as an example of a lightning strike to a fastener in 

an “oversized hole”. As shown in Figure 1, the minimum clearance between the screw 

and the various holes is two thousandths of an inch. 

Figure 1- Fuel Access Panel Installation 

GASKET 600-10189-1 

HOLE Ø.23-.32

CLAMP RING 600-10186-1 

HOLE Ø.251-.258 

CSK 100° x Ø.499 

OUTER DISH 600-10050-9 

HOLE Ø.310 

NUT PLATE NAS1473-A4 

Washer in nut plate: Ø.289 MIN 

Wing Plank 

MS24694-S103 

Screw diameter: Ø.246-249

Access Panel 

Dome Anchor Nut 
8 

4.2- Supplementary Exemption justification 

Further to item 4.1 above, BA will demonstrate that the CRJ1000 design is safe and 

justifies the exemption based on: 

- the BA service history of Regional & Business Jet wing designs (ref BA FRACAS 

tracking database), and 

- the low flammability exposure of the CRJ1000 wing fuel tank (Ref: BA substantiating 

report: RAP-IN670-172 Revision B-40 Addendum 37 (Design Compliance Report - Fuel System)

 4.2.1- Service History

BA manufactures all Regional and Challenger Business Jet wings in-house. The 

processes regarding wing tank fasteners installation are the same for all of these aircraft. 

Also, there have been no reported instances of loose fasteners or sealant degradation 

(through FRACAS data) on these aircraft for over 30 million flying hours (for CRJ’s 

alone) which includes nearly two full years of service of CRJ1000’s currently being 

operated by Britair and Air Nostrum. This is further supported by the high time fuel tank 

internal inspections performed, with Authority participation, related to the SFAR 88 

activity. No missing or damaged sealant was observed during these inspections. 

4.2.2 - Low Flammability Exposure

By definition, an aluminum wing with no significant internal or external heating source is 

considered of low flammability. As per the definition prescribed in FAA AC 25.981-2A, 

the wing design is a relatively thin design with a large surface area to volume ratio, 

providing good cooling characteristics (i.e. good cooling characteristics normally result in 

a surface to area volume ratio greater than 1.0; the CRJ1000 ratio is 1.7). For the center 

tank, assessments were performed for 14 CFR Part 26 compliance based on ground 

and flight tests conducted on CRJ700 aircraft, which have similar cooling characteristics 

as the CRJ1000. It has been demonstrated that the flammability exposure is less than 

7%, in accordance with the FAA Fuel Tank Flammability Assessment Model (Monte 

Carlo) as per Appendix N of Part 25 and FAA AC 25.981-2A. 

Ref: BA substantiating report: RAP-IN670-172 Revision B-40 Addendum 37 (Design 

Compliance Report - Fuel System 

5 - Conclusion on the Effect on Safety

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 sources is 

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

AC25.981-1B (noting that this AC did not address the “structural lightning” aspects) and 

the development of airworthiness limitations, both fuel 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 accomplished. All the resulting mandatory modifications are included as an 

integral part of the CRJ1000 type design. Low fuel tank flammability exposure has been 

demonstrated for 14 CFR Part 26.33 compliance as per FAA guidance AC 25.981-2A 

and Part 25 Appendix N. 
9 

BA considers the design of the CRJ1000 wing a safe design, with good service history 

and meets authority expectations for an aluminum wing design. The BA position is that 

granting this exemption has no impact on safety. 

6 - What factors were considered in the determination of public interest?

In accordance with TCCA Issue Paper AV-1, Edition 2,”Lightning Protection for the Fuel 

Tank Installation”, compliance to AWM 525.981(a)(3) with respect to lightning protection 

will require two independent and reliable means of protection for the wing fuel tank 

design of the CL-600-2E25. As stated earlier in this letter, BA will utilize this Issue Paper 

as an acceptable means of compliance to 14 CFR Part 25.981(a)(3) taking into account 

the guidelines of FAA Policy memo ANM-112-08-002. However due to the unexpected 

problems experienced during recent testing, BA requires the extra time needed to 

complete the remainder of the tasks necessary to demonstrate full compliance. BA has 

a high level of confidence (based on overall success of original testing) that we can 

achieve it. Not allowing additional time beyond Dec 17, 2012 to complete our activities 

can result in the absence of future sales to US operators who will not be allowed to 

operate a CRJ under the current terms of the exemption. 

This would in turn lead to a severe economical impact on BA, potentially resulting in a 

reduction in the workforce since the CRJ would have less of the market share in the 

United States in upcoming years (which will in turn result in fewer aircraft being built). In 

terms of our current and future customers, they will most likely absorb the impact of 

these delays/ cancellations among the flying public due to their inability to provide 

adequate and efficient service and as a result, increase ticket prices. 

Given that the testing activities has shown that the vast majority of the aircraft structure 

complies with 14 CFR Part 25.981(a)(3) for fault tolerance, allowing BA to demonstrate 

compliance to 14 CFR Part 25.981(a)(3) for the remaining areas would be reasonable 

when compared to the disruptions in delivery schedules and the potential economical 

impact (i.e. penalties, loss of revenue, potential workforce reductions) and the 

repercussions thereof (delayed entry into service, customer and public dissatisfaction) 

that come with these delays. 

Conclusion

With the commitment to perform additional testing / analysis over and above what was 

already done and the justification for the effect on safety and public interest, BA hereby 

requests that the current exemption 10175 be revised to allow for additional time for full 

compliance with 14 CFR Part 25.981(a)(3) up until Dec 17, 2015. 
10 

Attachment 2 to BA letter AW-CRJ/12/746 dated November 19, 2012 

Revised COMPLIANCE PLAN ADDRESSING 14 CFR Part 25.981(a)(3)

The purpose of this compliance plan is to provide details regarding BA’s approach to 

demonstrating compliance with the remaining activities related to compliance with 14 

CFR Part 25.981(a)(3) at Amendment 25-102. 

Requirement: 14 CFR Part 25.981(a)(3) 

Requirement text: “(a) No ignition source may be present at each point in the fuel 

 tank or the fuel tank system where a 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 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.

BA Disciplines 

Affected: Fuel Systems (primary), EMC, and Structures 

Approach to Compliance

Based on the compliance methodology used to generate FAA exemption no 10175, BA’s 

compliance plan for 14 CFR Part 25.981(a)(3) requires a 3-phased approach. The 

approach as originally communicated upon approval of the initial FAA exemption 

remains valid. This approach was summarized as follows: 

PHASE 1: Identification of Failure Modes (since completed) 

Structures: 

An integrated Product Development Team (IPDT) was created with members from 

Airworthiness, Design, Quality, Manufacturing and In-Service Engineering. The intent of 

this team was to analyze the structural wing tank design and consider any possible 

defect that could occur in the manufacturing process regardless of the probability of 

occurrence. In addition, consideration was also made to in-service findings that were 

reported to BA and the repeatability of these findings as well as any potential fatigue 

findings gathered from two lifetimes of fatigue testing on a full-scale test article. A set of 

failure modes was derived from this analysis. These results have been documented in 

report RAZ-BA698-017 Rev --, “CL-600-2E25 Wing Tank Structural Survey in Support of 

Compliance with AWM 525-14 CFR 25.981(a)(3)”. 
11 

PHASE 2: Classification of Failure Modes (since completed)

Structures: 

Each one of the agreed failure modes identified above in phase 1 were classified into 

one of the following categories: 

i) Not a potential ignition source; 

ii) Possible ignition source, fault tolerant; 

iii) Possible ignition source, not fault tolerant. 

It should be noted that this phase concentrates solely on classifying the failure modes 

into one of the 3 categories above. In case ii), BA has reviewed the design and noted 

that these failure modes are protected by two independent features that can potentially 

be fault tolerant. In case iii), the failure cases are protected by one design feature. 

Results of the classification of these failure modes are listed in RAZ-BA698-017 Rev A, 

which was further amended at Rev B to incorporate comments received from TCCA. 

PHASE 3: Substantiation via Test Data and Analysis (on-going)

Structures: 

The failure modes that are not ignition sources [category i) above] are eliminated in this 

phase. The other two categories are analyzed further. 

a) Fault tolerant items: BA has reviewed the list of these potentially fault tolerant items 

and has developed a test scenario that will prove the validity of these items as being 

fault tolerant. As part of phase 3, a test scenario has been submitted outlining the items 

which require further testing along with a schedule to conduct these tests post 

certification. 4 rounds of testing have since been completed but further actions remain. 

See conclusion. 

b) Not fault tolerant items: BA has reviewed the list of potentially non-fault tolerant items 

and has concluded that substantiation shall be submitted in the form of a reliability & 

safety assessment. BA will investigate whether there are practical design changes that 

could be implemented to make these items fault tolerant. If practical changes exits, BA 

will demonstrate compliance as outlined in a) above. If it is impractical to change the 

design to be fault tolerant, a safety assessment will be conducted to show that fuel tank 

vapor ignition is extremely improbable. 

Systems:

Fuel system elements and related components of the wing fuel tank design, full 

compliance has been demonstrated and documented in BA Fuel Tank System Safety – 

Ignition Prevention Report, RBR-BA690-144, as part of the CL-600-2E25 type 

certification activities. The details of this plan are outlined in the attached BA Fuel 

System internal memorandum CRJ1000/28/2010/001/EH dated Mar 29, 2010 

(Attachment 4) A schematic is shown on the next page, that outlines the 3-phased 

approach. 
12 

Summary of 3-phased approach (up to date status):

Systems Structure

N/A Identification of 

potential failure modes 

Classification of failure 

modes 

1) Ignition source 

2) Fault tolerant 

3) Not fault tolerant

N/A 

Provide test scenarios 

for fault tolerant items 

and safety analysis for 

non-fault tolerant items 

Use previous data from 

SFAR 88 / SCA H2002-03 

to outline failure modes, 

design changes, 

inspections and probability 

analysis 

Phase 1 

Phase 2 

Phase 3 

RAZ-BA698-017 Rev - - 

RAZ-BA698-017 Rev B 

RAZ-BA698-017 Rev C 

Fuel system Memo 

Compliance Compliance 

At the current time, Testing and analysis required to complete the activities of phase 3 has 

not yet been completed. The exemption request outlines compensating factors that 

demonstrate that the airplane is safe and that the time to perform the additional testing to 

achieve full compliance is acceptable and in the public interest. 
13 

Means/Method of Compliance

1) Fuel Systems (completed) 

MOC = Design Review (DR), Data (D), Analysis (A) 

Method of Compliance = A review of the design has shown that the CL-600-2E25 design 

changes do not impact the existing test data substantiation which demonstrates 

compliance with this requirement. This data shows that certain areas of the fuel tank 

design have been proven fault tolerant with a robust design, which precludes any ignition 

sources in that area. Regular inspections (where practical) exist as AWL items in our 

Maintenance Requirements Manual (MRM) can verify the functionality of these 

protective features. 

References: 

- Fuel system design compliance report RAP-IN670-172; 

- Fuel system memo CRJ1000/28/2010/001/EH dated 29 March 2010. 

2) EMC (MOC remains unchanged from previous exemption. MOC methodology is now 

being applied to remaining testing needed to be performed)

MOC = Design Review (DR), Data (D), Test (T), Analysis (A) 

Method of Compliance = A review of the design will show that the CL-600-2E25 design 

changes do not impact the existing test data substantiation which will be used to 

demonstrate compliance with this requirement for “Systems” only. This data will show 

that certain areas of the fuel tank design have been proven fault tolerant with a robust 

design, which precludes any ignition sources in that area. 

For structural design elements, test data will be provided for all elements of the structural 

design where fault tolerance has been identified. Where fault tolerance has not been 

identified, it will be shown via an analysis and/or test data that these areas are ones 

wherein fuel tank vapor ignition is extremely improbable. 

References: 

- EMC design compliance report RAE-BA670-176 “Aircraft Lightning Protection 

Design Compliance Report, Direct Effects”; 

- EMC memo CRJ900-01-66-2010-26A dated May 12, 2010. 
14 

Attachment 3 to BA letter AW-CRJ/12/746 dated November 19, 2012 

EMC memo, CRJ900-01-66-2012-33 dated Oct 12, 2012 (see next 

page) 

BT0043-02 MW97 2001-09 2 

1. References 

1.1. AWM 525.981(a)(3) 

1.2. TCCA document Fuel System Lightning Protection Certification Areas of Discussion Revised 

1/27/10 

1.3. TCCA Issue Paper AV-1 

1.4. AWM File 5009-6-525-4; RDIMS # 6151541 V3; NCR/RCN # 080-2010 Exemption from 

Paragraph 521.31(1)(d) of the Canadian Aviation Regulations only with respect to paragraph 

525.981(a)(3) of the Airworthiness Manual – Fuel Tank Explosion Prevention 

1.5. FAA draft document Policy Guidance for Fuel Tank Structural Lightning Protection Policy

1.6. RAZ-BA698-017 CL-600-2E25 Wing Tank Structural Survey in Support of Compliance with AWM 

525 / 14 CFR 25.981(a)(3) 

1.7. Memo CRJ900-01-66-2010-26A 25.981(a)(3) Structural Lightning Protection Phase 3 Plan 

1.8. Memo CRJ900-01-66-2010-62A 25.981(a)(3) Structural Lightning Protection Agreement Points – 

Pass Fail Criteria 

1.9. Memo CRJ900-01-66-2010-63A 25.981(a)(3) Structural Lightning Protection Agreement Points – 

Test Article Grouping 

1.10. Memo CRJ900-01-66-2010-64A 25.981(a)(3) Structural Lightning Protection Agreement Points – 

Approach for NFT Features 

1.11. Memo CRJ900-01-66-2010-65A 25.981(a)(3) Structural Lightning Protection Agreement Points – 

Internal Test Levels 

1.12. TDS-698-28-BA-2028 Rev A Lightning Test Procedure in Support of the CL698 25.981(a)(3) 

Structural Compliance Effort 

2. Test Campaign Status 

In accordance with ref 1.7 BA has proceeded with at test campaign in order to show compliance with 

AWM 525.981(a)(3) (ref 1.1) as described in TCCA issue paper AV-1 (Ref 1.3). This has continued post 

certification as permitted by the existing partial exemption (ref 1.4). 

In order to define the test cases, BA and TCCA first agreed on the applicable failure modes, on which of 

these were considered potential ignition sources (documented in ref 1.6), and subsequently on how the 

possible test articles could be grouped to reduce the number of test cases (documented in ref 1.9). 

Additionally, the pass/fail criteria were agreed (documented in ref 1.8) and the internal test levels were 

agreed (documented in ref 1.11). This ultimately resulted in the test plan (ref 1.12) which was used to 

conduct the test campaign. 

Testing was conducted in three stages from 6-8 Dec 2011, from 23-27 Jan 2012, and from 7-15 Mar 2012. 

Both BA and TCCA witnessed the testing during each stage. A summary of the test results is shown 

below.
BT0043-02 MW97 2001-09 3 

Category Defect Test type Result 

Skin-Rib interface Oversized hole (1 & 2 sizes too big) Zone 2A arc attachment to fastener Pass 

Hi-lite too long (1 & 2 sizes too long) Zone 2A arc attachment to fastener Pass 

Gap between parts Zone 2A arc attachment to fastener Pass 

Correct freeze plug Zone 2A arc attachment to fastener Pass 

Loose freeze plug Zone 2A arc attachment to fastener Pass 

Rib-Spar interface Oversized hole (1 & 2 sizes too big) Internal conduction (WF 5) Pass 

Hi-lite too long (1 & 2 sizes too long) Internal conduction (WF 5) Pass 

Correct freeze plug Internal conduction (WF 5) Pass 

Loose freeze plug Internal conduction (WF 5) Pass 

Rib-Standoff 

interface 

No defect Internal conduction (WF 5) Pass 

Oversized hole (1 & 2 sizes too big) Internal conduction (WF 5) Pass 

Rivet too long (1 & 2 sizes too long) Internal conduction (WF 5) Pass 

Wing to Fuselage 

Fitting 

No defect Zone 3 conduction Pass 

Bolt too long (1 & 2 sizes too long) Zone 3 conduction Pass 

Outboard fuel access 

panel 

Missing brush sealant on dome nut Zone 3 conduction Pass 

Zone 3 arc attachment to fastener Pass 

Electrical bonding area degraded Zone 3 conduction Pass 

Zone 3 arc attachment to fastener Pass 

Zone 3 arc attachment to panel Pass 

Conductive gasket missing Zone 3 conduction Pass 

Zone 3 arc attachment to fastener Pass 

Zone 3 arc attachment to panel Pass 

Inboard fuel access 

panel 

Missing brush sealant on dome nut Zone 2A arc attachment to fastener Pass 

Electrical bonding area degraded Zone 2A arc attachment to fastener Pass 

Zone 2A arc attachment to panel Pass 

Conductive gasket missing Zone 2A arc attachment to fastener Pass 

Zone 2A arc attachment to panel Pass 

Water drain valve Broken O-Ring Zone 2A arc attachment to valve Pass 

Zone 2A arc attachment to fastener Not Pass 

Electrical bonding area missing Zone 2A arc attachment to valve Not Pass 

Zone 2A arc attachment to fastener Not Pass 

No brush sealant Zone 2A arc attachment to valve Pass 

Zone 2A arc attachment to fastener Not Pass 

Spar splice No pack sealant Internal conduction (WF 5) Pass 

Table 1 - Test Summary 
BT0043-02 MW97 2001-09 4 

As can be seen the Table 1 above, the CRJ1000 wing structure design was found to be fault tolerant in all 

cases except the following: 

1. Water drain valve retainer fasteners were found to not meet lightning requirements. 

2. Water drain valve was found to not be fault tolerant to the defect scenario where the electrical 

bonding area is missing. 

BA therefore proposes the way forward for each of these cases as detailed in the following paragraphs. 

Refer to enclosed Gantt chart for overall schedule 

3. Way Forward for WDV Retainer Fasteners 

BA has conducted a design review of the WDV retainer fasteners in order to identify possible 

modifications the design such that the retainer fasteners will be compliant with the lightning regulations. 

The proposed design will next be evaluated to determine all applicable failure modes of the fasteners. BA 

will then review existing data to determine if it is sufficient to demonstrate fault tolerance of the modified 

fastener design. If the existing data is found to be insufficient to demonstrate fault tolerance, additional 

testing will be conducted to show compliance. 

4. Way Forward for WDV 

The way forward for the WDV is split into different sub-sections in order to maximize efficiency and cover 

all contingencies. The following sections outline the plan. 

4.1. Assessment of Design vs Test 

BA has noted that the test case where the WDV failed is extremely severe; the complete electrical bonding 

surface is missing. Preliminary discussions with BA in-service engineering have indicated they have not 

received any reports of corrosion between the wing plank and the flanges of the WDVs. Therefore, BA 

will assess whether the tested case is in fact representative of an actual failure mode or if this case was 

overly severe. A sampling program of high time aircraft will be conducted to determine the expected 

extent of corrosion on the WDV electrical bonding surface. BA will document its position along with 

substantiating data and presented it to TCCA for agreement. If it is found that the case is not realistic, BA 

will assess if additional testing is needed or if existing test data is sufficient to demonstrate fault tolerance 

of the WDV. If the existing data is found to be insufficient to demonstrate fault tolerance, additional 

testing will be conducted to show compliance. 

4.2. Investigation of Alternate Design Options 

In parallel with activity 4.1, BA will initiate a dedicated review team to investigate alternate design options 

for the WDVs. This assessment will be required in the event that BA is unable to show via the assessment 

in activity 4.1 that the current WDV design is fault tolerant however it is conducted in parallel to reduce the 

potential impact if it is need. Additionally, it comprises one of the BA action items from BA-TCCA 

meeting 30 Apr 12. 
BT0043-02 MW97 2001-09 5 

The team will investigate alternate design options to determine whether a design exists that is fault tolerant 

to all possible failure scenarios (including degraded electrical bonding). This will include, among other 

possibilities, investigating with fuel component suppliers into existing alternate designs of the water drain 

valve itself. 

If a potential design change is identified that could be shown to be fault tolerant the team will evaluated the 

design to determine all applicable failure modes and review existing data to determine if it is sufficient to 

demonstrate fault tolerance of the modified valve design. If the existing data is found to be insufficient to 

demonstrate fault tolerance, additional testing will be necessary to show compliance. If the design is found 

to be fault tolerant, BA will assess the practicality of implementing this design. 

It should be noted that this scenario caries a risk of invalidating the work done per section 3 above, since it 

may result in a modified attachment scheme which does not use the same type of fasteners. 

The worst case estimate is made assuming a new WDV design is required from the fuel component 

supplier. 

4.3. Prepare Probability Based Safety Assessment 

In parallel with activity 4.1 and 4.2, BA will conduct a probability based safety assessment of the WDV 

(per agreed approach for NFT features documented in ref 1.10). This analysis will be used in the event that 

BA is unable to show via the assessment in activity 4.1 that the current WDV design is fault tolerant and is 

not able to find a practical, fault tolerant, alternate design in activity 4.2. 

As part of the probability based safety assessment it is required to determine the sparking threshold of the 

WDV in the case where the electrical bonding is degraded. This requires additional testing to be 

conducted. 

5. Exemption Extension 

Due to the extensive amount of work required for the way forward plan to show compliance, BA is 

requesting an extension to the existing exemption for only the areas discussed in 3 and 4 above. The 

extension is required since it is not feasible for BA to complete all the above activities before the expiry 

date of 29 Oct 2012 of the current exemption. BA requests that the exemption be extended per the attached 

schedule which is based on the worst case estimates for completion of all above activities. 

For all areas of the fuel tank structure where the testing passed, BA will prepare the documentation 

required to show compliance with AWM 525.981(a)(3) as described in issue paper AV-1 prior to the expiry 

date of the current exemption. 
ID Task Name Duration Start Finish

1 25.981(a)(3) Exemption Extension for WDV and WDV Housing Fastener Compliance 673 days Mon 11/5/12 Wed 9/16/152 Finalize Preliminary Concepts 46 days Mon 11/5/12 Mon 1/21/133 Conduct reviews of preliminary design concept to identify failure modes and prote 20 days Mon 11/5/12 Fri 11/30/12

4 Preliminary concept frozen 1 day Mon 12/3/12 Mon 12/3/125 Complete DV engineering of agreed design concept 25 days Tue 12/4/12 Mon 1/21/136 Update RAZ-BA698-017 with design concept, failure mode, and protection feature 10 days Tue 12/4/12 Mon 12/17/127 Review RAZ-BA698-017 Rev D with TCCA 5 days Tue 12/18/12 Mon 1/7/138 TCCA agreement of RAZ-BA698-017 Rev D 1 day Tue 1/8/13 Tue 1/8/139 Test Article Design and Build 230 days Wed 1/9/13 Tue 12/17/13

10 Prepare 'paper' test articles 15 days Wed 1/9/13 Tue 1/29/1311 Review 'paper' test articles with TCCA 10 days Wed 1/30/13 Tue 2/12/1312 Review 'paper' test articles with BAEX 10 days Wed 1/30/13 Tue 2/12/1313 Test article concept frozen 1 day Wed 2/13/13 Wed 2/13/1314 Prepare test article engineering 30 days Thu 2/14/13 Wed 3/27/1315 Order prototype parts for testing 1 day Wed 1/30/13 Wed 1/30/1316 Receive prototype parts for testing 1 day Mon 6/10/13 Mon 6/10/1317 Test article construction 120 days Tue 6/11/13 Mon 12/16/1318 Conformity inspection 1 day Tue 12/17/13 Tue 12/17/1319 Test Documentation 36 days Wed 2/13/13 Wed 4/3/1320 Prepare TDS 15 days Wed 2/13/13 Tue 3/5/1321 Prepare FTER 15 days Wed 3/6/13 Tue 3/26/1322 Review TDS and FTER with TCCA 5 days Wed 3/27/13 Tue 4/2/1323 TDS and FTER approved 1 day Wed 4/3/13 Wed 4/3/1324 Testing 80 days Wed 12/18/13 Tue 4/22/14

25 Ship test articles to lab 10 days Wed 12/18/13 Tue 1/14/1426 Testing 40 days Wed 1/15/14 Tue 3/11/1427 Ship test articles to BA 10 days Wed 3/12/14 Tue 3/25/1428 Receive lab test report draft 1 day Fri 4/4/14 Fri 4/4/1429 Review and revision of lab test report 10 days Mon 4/7/14 Fri 4/18/1430 Receive final lab test report 1 day Mon 4/21/14 Mon 4/21/1431 TDI of test articles at BAEX (if required) 10 days Wed 3/26/14 Tue 4/8/1432 Present results of testing and TDI to TCCA 10 days Wed 4/9/14 Tue 4/22/1433 Final Documentation 78 days Mon 4/21/14 Wed 8/27/1434 Prepare top level BA test report 20 days Mon 4/21/14 Fri 5/16/1435 Internal review and revision of top level BA test report 5 days Mon 5/19/14 Fri 5/23/1436 Submission of test report to TCCA 1 day Mon 5/26/14 Mon 5/26/1437 Update RAZ-BA698-017 with test results (rev E) 10 days Tue 5/27/14 Mon 6/9/1438 Internal review and revision of RAZ-BA698-017 Rev E 5 days Tue 6/10/14 Mon 6/16/1439 Review RAZ-BA698-017 Rev E with TCCA 5 days Tue 6/17/14 Mon 6/23/1440 Submission of RAZ-BA698-017 Rev E to TCCA 1 day Tue 6/24/14 Tue 6/24/1441 Update RAE-BA670-176 with results of 25.981(a)(3) testing 20 days Wed 6/25/14 Tue 7/22/1442 Internal review and revision of RAE-BA670-176 5 days Wed 7/23/14 Tue 8/19/1443 Review of RAE-BA670-176 with TCCA 5 days Wed 8/20/14 Tue 8/26/1444 Submission of RAE-BA670-176 to TCCA 1 day Wed 8/27/14 Wed 8/27/1445 Completion of design and implementation 250 days Thu 8/28/14 Wed 9/16/1546 Design 125 days Thu 8/28/14 Wed 3/4/1547 Implement production and in-service (including SOC) 125 days Thu 3/5/15 Wed 9/16/15

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Page 1

Project: 981_plan.mppDate: Fri 10/12/12
15 

Attachment 4 to BA letter AW-CRJ/12/746 dated November 19, 2012 

Fuel System Memo CRJ1000/28/2010/001/EH dated 31 March 2010 

(see next page) 
MEMO 

DATE 31 March 2010 

SUBJECT CL-600-2E25 (CRJ1000) Fuel Tank Ignition Prevention – Aircraft 

Systems; AWM 525 / 14 CFR 25.981(a) 

FROM Endro Haryono 

TO Baljeet Manhas 

CC Alain Loranger, Geoffrey Armstrong, Fidelio Eugenio, Guy De Langis, , 

Branko Petrovic, Peter Stoyel, Francois Hopkins, Ghislain Grenier, 

James Moran, Gordon A. MacMillan, Johan Kohler 

REFERENCE CRJ1000/28/2010/001/EH 

1. References

a. RBR-BA690-144 – Fuel Tank System Safety - Ignition Prevention Report 

b. Special Condition Airworthiness (SCA) H2002-03 - Fuel Tank System Safety - Ignition 

Prevention Report 

c. Policy Guidance for Fuel Tank Structural Lightning Protection Policy – Final Draft 

d. RAP-IN670-173 – Fuel Tank Flammability Exposure Analysis 

e. FAA approval of Bombardier CRJ Flammability Analysis Report dated 6 August 2009. 

f. RAZ-BA698-017 – CL600-2E25 Wing Tank Structural Survey in Support of Compliance 

with AWM 525 / 14 CFR 25.981(a)(3) 

2. Background

The FAA issued a policy to determine the regulatory path of fuel tank lightning protection 

(Reference 1.c). It is stated that this policy is only applicable to the fuel tank structure and does 

not apply to lightning protection of the system components. 

This memo outlines the safety assessment that was done on the CL-600-2D24 aircraft systems 

to demonstrate compliance to SCA H2002-03 (Reference 1.b), which will also be used to show 

compliance to AWM 525 / 14 CFR 25.981(a) for the CL-600-2E25. 

Also, as defined in the FAA guidance, the requirement for either a special condition or 

petitioning for an exemption is dependent upon fuel tank flammability exposure. Hence in 

addition, this memo summarizes the CRJ1000’s fuel tank flammability exposure (Reference 

1.e). 
2 

3. Fuel Tank Ignition Prevention

a. Design Changes 

In general, the CRJ1000 system design is similar to the CRJ700/900. A couple of design 

changes in the fuel tank or adjacent of the fuel tank were introduced. None of the changes have 

a negative impact to the fuel tank ignition prevention. 

The following changes will be reported in the updated RBR-BA690-144 (Reference 1.a): 

i. As a result of a longer wingspan, lengthening of Slat #3 and corresponding piccolo tube by 

29.5” to each wing was required. 

The bleed air ducting within the center fuselage for the WAI system (LH+RH) increased in 

length by approximately 56” due to the center fuselage extension. A modification of fuse to 

wing bleed air duct was made to accommodate the lower wing. This change does not affect 

the bleed duct length in the belly fairing area. 

The new bleed duct shroud was modified from the existing CRJ700/900, which is made 

from a polyamide layer impregnated with steel foil instead of silicone impregnated fibber. 

The inner duct material remains as CRES 321. Bleed leak detection is routed along the 

bleed duct insulation vent hole and couplings. 

ii. Flux Detection Unit (FDU) is not implemented for the CRJ1000. 

b. Aircraft System - Safety Assessment 

The detail assessment of the aircraft systems is documented in the report RBR-BA690-144 

(Reference 1.a), and the modifications will be addressed in a new revision to the report. The 

assessment includes a list of affected system components, failure modes and potential effects 

to the aircraft (Refer to Appendix A). 

c. Aircraft System – Lightning and Electrostatic Discharge Protection 

The system components mounted on the fuel tank structure, which may potentially cause an 

ignition source (spark) if improper electrical bonding or another failure case is combined with a 

lightning strike or electrostatic discharge, will be addressed separately in RAZ-BA698-017. 
3 

4. Airworthiness Limitation

Airworthiness limitation(s) would be applied to ensure that possible ignition sources in the fuel 

tanks are identified and precluded by design changes or maintenance actions. 

a. Critical Design Configuration Control Limitation (CDCCL) 

The CDCCL list will be published as a part of the Maintenance Requirement Manual (MRM). 

The CDCCL provides instructions to retain the critical ignition source prevention feature during 

configuration changes that may be caused by component substitutions, alterations, repairs or 

maintenance actions. The CRJ1000 CDCCL list would be identical to the existing CRJ700/900 

(Refer to the Appendix B). 

b. Fuel System Limitation (FSL) 

A periodic inspection would be applied against the critical component to ensure an equivalent 

level of safety. The list of component, task and interval will be published in the MRM. The 

CRJ1000 FSL list would be identical to the existing CRJ700/900 (Refer to the Appendix C). 

5. Fuel Tank Flammability 

The CRJ1000 fuel tank flammability exposure analysis was determined based on guidance 

given in FAA AC 25.981-2A and Part 25 Appendix N. 

According to this method, a qualitative assessment is used to determine wing fuel tank 

flammability. The center fuel tank flammability exposure was analyzed using the FTFAM/Monte 

Carlo Analysis methodology as per Appendix N of Part 25. 

The fuel tank flammability analysis has been completed based on aircraft test results and is 

documented in RAP-IN670-173 (Reference 1.d). 

a. Wing Tank 

As per the criteria defined in the FAA AC 25.981-2A, it is shown that the wing main fuel tanks 

are categorized as conventional aluminum with no heating source. Hence it is considered as 

having low flammability. Detailed assessments are presented in the BA report RAP-IN670-173 

(Reference 1.d). 

5 

APPENDIX A 

Potential Ignition Source Hazard Assessment 

(RBR-BA690-144) 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

27-60 1 Multi-Function 

Spoilers Wiring chaffing in conduit. 

All Electrical arc 

Ignition Source in Fuel Tank in the event of conduit burn through, and Hot Surface Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 2 Engine Feed 

Boost Pump wiring chaffing in Aluminum conduit. 

All Electrical arc 

Ignition Source in Fuel Tank in the event of conduit burn through, and Hot Surface Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 3 Engine Feed 

Boost Pump failures increasing Canister temperature > 204°C. 

All Hot Surface 

Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 4 Engine Boost 

Pump produces electrical arcs from internal component failures or wire chaffing. 

All Electrical Arc 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 5 Engine Feed 

Boost Pump produces friction sparks from internal components. 

All Friction Spark 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 6 Impeller to 

housing contact in Boost Pump. 

All Friction Sparks 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 7 Ingestion of FOD 

in Boost Pump Impeller. 

All Friction Sparks 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 8 FOD Ingestion or 

component failures causing Boost Pump Motor to stall heating windings >204°C. 

All Hot Surface 

Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 9 APU Fuel Pump 

failures increasing Canister temperature > 204°C. 

All Hot Surface 

Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 10 APU Fuel Pump 

produces electrical arcs from internal component failures or wire chaffing. 

All Electrical Arc 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 11 APU Fuel Boost 

Pump produces friction sparks from internal components. 

All Friction Spark 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 12 Impeller to 

housing contact in APU Fuel Pump. 

All Friction Sparks 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 13 Ingestion of FOD 

in APU Fuel Pump Impeller. 

All Friction Sparks 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 14 Fuel Transfer 

SOV body heating >204°C. 

All Hot Surface 

Ignition source in Fuel Tank 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 15 Cross-Flow Pump 

Failures increasing Temperature >204°C. 

All Hot Surface 

Ignition Source in Tank 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 16 Cross-Flow Pump 

produces electrical arcs from internal component failures or wiring chaffing. 

All Electrical Arc 

Ignition source in fuel tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 17 Cross-Flow Pump 

produces friction sparks from internal components. 

All Friction Spark 

Ignition Source in fuel tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 18 Ingestion of FOD 

in Cross-Flow Pump Vane elements. 

All Friction Spark 

Ignition Source in fuel tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 19 FOD ingestion of 

component failures causing Cross-Flow Pump motor to stall, heating winding >204°C. 

All Hot Surface 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification Testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-20 20 Gravity Transfer 

SOV motor heating >204°C. 

FLT Hot Surface 

Ignition source in Fuel Tank through Fuel tank wall. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification Testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-20 21 Refuel Defuel 

SOV Solenoid heating >204°C. 

GND Hot Surface 

Ignition source in Refuel/Defuel Manifold Housing. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification Testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-40 22 Fuel Quantity 

Gauging Computer failure causing highenergy output to Fuel Quantity Probes. 

All Hot Surface 

Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-40 23 Fuel Quantity 

gauging wiring chaffing with power wiring causing capacitance probe diode heating >204°C. 

All Hot Surface 

Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Qualification testing. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-40 24 Fuel Quantity 

gauging wiring chaffing with power wiring causing electrical discharge across gap. 

All Electrical Arc 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-40 25 Fuel Quantity 

gauging wiring chaffing in tank. 

All Electrical Arc 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-40 26 Fuel Temperature 

Probes wiring chaffing with high-energy wiring resulting in probe heating to >204°C. 

All Hot Surface 

Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-40 27 High Level 

Sensor Probe glass bead failure. 

All Filament Heating 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-40 28 High Level 

Sensor Probe glass bead heats >204°C from wiring chaffing with high-energy wiring. 

All Hot Surface 

Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

28-40 29 Pressure Sensor 

diaphragm failure resulting in microswitch and wiring exposure to vapor. 

All Electrical Arc 

Ignition Source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

28-40 30 Scavenge Ejector 

Delta-P Sensor Switch heats >204°C from wiring chaffing with high-energy wiring. 

GND Hot Surface 

Ignition source in Fuel Tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

29-00 31 Hydraulic Fluid 

Overheat >204°C in hydraulic lines passing through fuel tanks. 

All Hot surface 

Ignition source in fuel tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Thermal Analysis and tests. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 

33-40 32 Landing and Taxi 

Lights compartment temperature heats wing tank surface >204°C. 

GND Hot surface 

Ignition source in fuel tank. 

FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Thermal Analysis. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

36-10 33 Bleed duct leak 

over centre fuel tank heating centre tank surface>204°C. 

All Hot surface 

Ignition source in fuel tank. 

FAR 25.901 FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Thermal Analysis. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
ATA ITEM 

NO 

HYPOTHETICAL COMPONENT FAILURE 

FLIGHT PHASE 

POTENTIAL EFFECT ON AIRCRAFT 

REQUIREMENT METHOD OF 

EVALUATION 

ASSESSMENT REPORT SECTION 

36-10 34 Anti-Ice duct 

overheat heating front spar surface>204°C. 

All Hot surface 

Ignition source in fuel tank. 

FAR 25.901 FAR 25.981 FAR 25.1309 

Fuel Tank System Safety Review. Thermal analysis. 

RBR-BA690-144 The appropriate sections of the report will be updated to show compliance for CRJ1000. The updated reporwill be submitted as part of basic type certification. 
6 

APPENDIX B 

Critical Design Configuration Control Limitation (CDCCL) 

Maintenance Requirement Manual (MRM) CSP B-053 
AIRWORTHINESS LIMITATIONS

TEMPORARY REVISION 2−268

Airworthiness LimitationsPart 2 of Maintenance Requirements ManualSection 3 − Fuel System Limitations

Table 1 − List of Critical Design Configuration Control Limitations (CDCCL)

CDCCL ITEMS CRITICAL IGNITION PREVENTION FEATURE MANUAL REFERENCE 

Pink striped protectivesleevesor,Production − Pink WireJacket W22 Code

Chaffing of Gauging wire with power wires causing fuelprobe overheat

WDM 28−40−00 

Front spar wire clippingfailure inspection

Chaffing of Gauging wire with power wires causing fuelprobe overheat

AMM 24−90−00−220−80

Self−bonding couplings infuel tanks. P/ N 14J26,LC459

Bonding of fuel and vent lines for lightning protection AMM 51−80−00−760−802 

LRU Sealant inspection Preventing arc forming in gaps due to lightning AMM 28−00−00−220−80Thermal Fuse assembly onHydraulic System #1 and#2

Preventing Hydraulic System overheat by dumpinghydraulic fluid overboard before it reaches the Fuel Tankauto−ignition temperature

AMM 29−11−14−961−80

CL 600 2C10, CL 600 2D15, CL 600 2D24
7 

APPENDIX C 

Fuel System Limitation (FSL) 

Maintenance Requirement Manual (MRM) CSP B-053 
TASK

NUMBER

TASK CODE/

TASK TITLE/

TASK DESCRIPTION

FUEL SYSTEM LIMITATIONS

MODEL

EFFECTIVITY AMTOSS

CL-600-2C10, CL-600-2D15 and CL-600-2D24

AIRWORTHINESS LIMITATIONS

B

24-90-00-601 FUEL TANK WIRING HARNESS INSTALLATION: Detail Inspection 

of the fuel tank wiring harness installation in the fuselage for condition and security.

All 24-90-00-220-802

24-90-00-602 FUEL TANK WIRING HARNESS INSTALLATION: Detail inspection 

of the fuel tank wiring harness installation at the center tank front spar for condition and security.

All 24-90-00-220-801

28-00-00-601 FUEL TANK LINE REPLACEABLE UNIT SEALANT: Detail 

Inspection of all the fuel Tank LRUs to ensure the condition and integrity of the sealant around their mounting surfaces and attachments.

All 28-00-00-220-801

28-11-23-601 FUEL STOWAGE SYSTEM PIPE: Functional check to ensure that 

the electrical bonding values of the Fuel Stowage System Pipe Assy`s is within tolerannce.

All 28-11-23-720-801

28-11-23-602 FUEL STOWAGE SYSTEM PIPE BONDING JUMPER: Detail 

inspection of the Fuel Stowage System Pipe Bonding Jumpers for condition and security.

All 28-11-23-220-801

28-12-13-601 CLIMB VENT LOOP BOOT ASSEMBLY AND DRAINAGE TUBE: 

Detail inspection of the climb vent loop boot assy`s and drainage tubes for condition and security.

All 28-12-13-220-801

29-30-00-601 HYDRAULIC SYSTEM # 3 TEMPERATURE TRANSDUCER: 

Operational check of the Hydraulic System # 3 Temperature Transducer via EICAS

All 29-36-00-710-801

29-30-00-602 HYDRAULIC SYSTEM # 3 TEMPERATURE TRANSDUCER: 

Discard the Hydraulic System # 3 Temperature Transducer

All 29-36-03-961-801

Airworthiness LimitationsPart 2 of Maintenance Requirements ManualSection 3 - Fuel System Limitations

See Effective TR
TEMPORARY REVISION 2−269

The contents of this Temporary Revision have been approved by the Chief, Engineering (or designate), National Aircraft Cerification Canada Civil AviationDate October 10, 2008 Signed Roop Dhaliwal

FILING INSTRUCTIONS: Insert this Temporary Revision (TR) 2−269 facing page 2−3−5 in Part 2 of the Maintena

Manual.Record the incorporation of this Temporary Revision on the yellow RECORD OF TEMPsheet at the front of this Part.Keep this Temporary Revision until normal revision service incorporates this informatioRequirements Manual.

DESCRIPTION: To add TASK NUMBER 29−30−00−603.

TASK

NUMBER

MODEL

EFFECTIVITY AMTOSS

TASK CODE/

TASK TITLE/

TASK DESCRIPTION

29−30−00−603 ALL 29−11−14−961−801 HYDRAULIC SYSTEM #1 and #2 THERMAL FUSE: Discard the

system #1 and #2 thermal fuse (Post Modsum 670T112042 or S670BA−29−005)

CL−600−2C10, CL−600−2D15 AND CL−600−2D24

AIRWORTHINESS LIMITATIONS

Airworthiness LimitationsPart 2 of Maintenance Requirements ManualSection 3 − Fuel System Limitations

CL 600 2C10, CL 600 2D15, CL 600 2D24
16 

Attachment 5 to BA letter AW-CRJ/12/746 dated November 19, 2012 

RMAS Memo: Procedure for the Numerical Probability Assessment of 

the CRJ-1000 Fuel Tank Structural Non-Fault Tolerant Feature 

Failures, dated March 29, 2010. (see next page) 

 
MEMO 

DATE March 29, 2010 

SUBJECT Procedure for the numerical probability assessment of the CRJ-1000 

fuel tank structural Non-Fault Tolerant Feature Failures 

FROM Z. Klim, J-P. Dargis 

TO B. Manhas 

CC R. Heppell 

Reference: 

1. Policy Guidance for Fuel Tank Structural Lightning Protection Policy, 2010 

2. RAZ-BA698-017, Rev.A, Wing Tank Structural Survey in Support with Compliance with 

AWM525 /14CFR 25.981(a) (3) 

1. Introduction 

This Memo provides BA approach to establish compliance with current regulatory standards 

applicable to lightning protection of the CRJ-1000 fuel tank structure for Non-Fault Tolerant 

Feature Failures by numerical probability assessment. The proposed procedure is using the 

criteria defined in the FAA Policy Guidance for Fuel Tank Structural Lightning Protection Policy 

(ref.1) and is aligned with the regulatory path described as petitioning for an exemption. 

For areas of the design where it is found to be impractical to provide fault tolerance, the required 

numerical probability assessment will be conducted to ensure a fuel vapor ignition is extremely 

improbable. An extremely improbable probability is described in AC 25.981-1C as failure 

conditions so unlikely that they are not anticipated to occur during the entire operational life of 

all airplanes of one type. Numerically this is defined to be less than 1 x 10-9 events per flight 

hour. The purpose of the assessment is to substantiate that the probability of failures associated 

with non-fault tolerant features that might lead to a fuel tank explosion is in extremely 

improbable category. 

2. General Approach to the Numerical Probability Assessment 

The relevant non-fault tolerant structural design areas that may contribute to ignition sources 

inside the fuel tank when a failure occurs will be identified. Each type of non-fault tolerant 

feature failure will be assessed and the result will be summed. 

Once the non-fault tolerant feature failure (NFTFF) types are identified, their failure rates will be 

determined using the available data. Some additional factors might be considered when 
2 

determining failure rates including the configuration or design specific details as described in the 

Policy. 

The main steps of the process leading to the identification and numerical probability assessment 

of the NFTFFs are described below: 

1. Identify potential failure modes 

2. Assess failure condition 

3. Determine fault tolerance 

4. Determine practicality of providing fault tolerance 

The set of the potential failure modes regardless of the probability of occurrence was 

established by performing a complete wing tank survey in pertinent areas related to fuel tank 

lightning protection as defined FAA “Policy Guidance for Fuel Tank Structural Lightning 

Protection”(ref.1). If the failure assessment results in demonstrating that the design is free from 

ignition sources after assessment of relevant single failure conditions, then the design is 

considered to be fault tolerant. If not, then further analysis is required per numerical probability 

assessment for the Non-Fault Tolerant Feature Failures. The subset of NFTFFs was defined 

and the numerical probability assessment will be performed according to the guideline provided 

in section 3.5 of the Policy. 

3. Numerical Probability Assessment 

The purpose of this assessment is to substantiate that it is extremely improbable that failures 

associated with non-fault tolerant features will lead to a fuel tank explosion. The sample fault 

tree diagram in Figure 1 provides an example of a fault logic structure that will be used for 

conducting this numerical assessment. Basic events are user supplied probability inputs, which 

will be assessed based on the available data, tests and recommendation from the Policy. After 

that, these probabilities will be multiplied together when linked by an “AND” gate or summed 

together when linked by an “OR” gate. The relevant non-fault tolerant structural design areas 

that may contribute to ignition sources inside the fuel tank when a failure occurs will be 

identified. Each type of non-fault tolerant feature failure will be assessed and the result 

summed. To be compliant, the top-level event must result in a numerical value less than 1 x 10-9

events per flight hour. The steps related to the probability inputs assessment and analyses are 

described below. 
3 

Figure 1 – Procedure of the analysis for numerical probability assessment of the NFTFFs 

Step 1 – probability of lightning attachment to aircraft per flight hour will be assessed based on 

the available data and the recommendation from the Policy. According to the AC20-155 and 

ARP5412A the probability of lightning attachment to aircraft vary between 1/1000 and 1/20 000. 

Nominal probability is considered to be: 1/3000. Therefore the probability of 3E-4 can be used 

3.11

Overall 

Probability 

of Fuel Vapor 

Ignition Event

3.9

Overall Spark 

Probability at 

NFTFF1

3.10

Fleet Average 

Flammability 

Exposure

(FEET)

3.7/3.9

Failure 

Probability of 

NFTFF1

Factor for 

Current 

Exceeding 

Sparking 

Threshold for 

NFTFF1

Probability of 

Vapor Ignition due 

to Non-Fault 

Tolerant Feature 

Failure 1 

(NFTFF1)

3.9

Current 

Exceeds 

Sparking 

Threshold at 

NFTFF1

Probability of 

Vapor Ignition due 

to Non-Fault 

Tolerant Feature 

Failure 2 

(NFTFF2)

Overall 

Probability 

of Attachment to 

General Area of 

NFTFF1

Probability of 

Lightning 

Attachment to 

Aircraft Per 

Flight Hour

Distribution 

Factor for 

Attachment to 

General Area of 

NFTFF1

Probability of 

Vapor Ignition due 

to Non-Fault 

Tolerant Feature 

Failure 3 

(NFTFF3)

Criteria: Overall Probability of 

Fuel Vapor Ignition Event ≤ 1E-9

Typically 3E-4 See Table 3.9-1

See Figures 3.9-1 

and 3.9-2

1 2

3

4 

5 

6 
4 

for the purpose of this analysis as recommended by the Policy. BA field data will be used also to 

assess this probability. 

Step 2 – distribution factor for attachment to general area of the aircraft will be obtained by 

combining the probability of lightning attachment to an aircraft with a distribution of initial 

lightning attachment locations on an aircraft (i.e. the percentage of lightning attachments to 

initial entry and exit locations). While there can be several possible combinations of initial 

lightning entry and exit locations per lightning strike event, for purpose of this analysis only one 

set of initial lightning attachment locations (i.e. one “entry” and one “exit” point) will be assumed. 

The distribution of initial attachment locations will be obtained from manufacturers’ data or the 

generic numbers as provided in Table 3.9-1 of the Policy. 

Step 3 – factor for current exceeding sparking threshold in a joint that would potentially cause 

an ignition source given a failure condition will be established. While there are various lightning 

current components and energy parameters that can influence ignition sources, for this 

numerical probability assessment it is acceptable to simplify things by using a peak stroke 

current distribution for the lightning threat exceedance curves. Acceptable peak current 

distributions for Zone 1 and Zone 2 threats are provided in Figures 3.9-1 and 3.9-2 (ref.1). The 

ignition source (sparking) threshold data (kA) will be determined using test objects containing 

the fastened or bonded joint with the failure condition implemented. The result of this activity will 

be amplitudes of direct strike or conducted lightning currents in kiloamperes (kA) that are the 

maximum levels where ignition sources should not occur under specific failure conditions. This 

ignition source threshold must be compared with results of analysis to determine what 

conducted current levels are expected at non-fault tolerant features. The exceedance probability 

results are based upon the ratio of the sparking threshold over joint current conducted by the 

fastener to interior structure and scaling by a full threat stroke current factor. The exceedance 

probability value will be taken from Figure 3.9-1 or Figure 3.9-2 for the respective zones. 

Step 4 – failure probability of NFTFF will be determined using all available data from the field. 

Numerical analysis methods and engineering judgment will be used to estimate these failure 

rates based on conservative assumptions. For most structural lightning protection features, the 

failure modes are latent which means that once failed they will be failed until repaired or until the 

end of the airplane life. The NFTFF average probability of failure will be considered for latent 

failure modes and normalized value per flight hour will be used in the probability calculation as 

recommended by the Policy. 

Step 5 – fleet average flammability exposure is defined as a percentage of the total flight time, 

including from preflight through disembarking and unloading cargo, that the fuel tank is 

considered flammable. According to the Policy for existing type certificated aircraft with a 

passenger capacity of 30 or more or a payload capacity of 7500 pounds or more subject to the 

provisions of 14 CFR Part 26, it is permissible to utilize the value of 7% as a default flammability 

exposure for those applicants not otherwise required to meet the requirements of Appendix M