GCF-0989/2011 – 2/6

14 CFR 11.81 (a) - Contact Information: 

Sérgio Augusto Viana de Carvalho 

Embraer Airworthiness Manager 

Av. Brigadeiro Faria Lima, 2170 – PC 179 

12227-901 São Jose dos Campos, SP - Brazil 

Phone: 55-12-3927-3543 

Fax: 55-12-3927-1184 

14 CFR 11.81 (b) Specific Section from Which Exemption is required

14CFR 25.981 (a)(3), amendment 25-102. 

(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 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.

14 CFR 11.81 (c) Extent of Relief and Reason for Seeking Relief 

Petition and General Information

Embraer has concluded that compliance to 14 CFR 25.981(a)(3) for fuel tank structural 

lightning protection would require three independent layers of protection. 

No viable means of lightning protection are envisioned in present construction 

technology that could address the three layers of protection for certain areas of the fuel 

tank structure. Particularly, fatigue cracking in structural elements of the fuel tank, and 

failure of highly loaded fuel tank fasteners leading to a separation from the hole or 

consequent failure of cap seal, present most difficulties in terms of means of 

compliance. Periodic inspection to monitor the condition of each fuel tank fastener is 

considered impractical due to the number (thousands) and location (difficult access). 

Frequently accessing the fuel tanks for inspection also increases the risk of causing 
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damage to components inside the tanks or to lightning protective features, which is 

detrimental to the safety objectives. 

Therefore, an exemption is being petitioned following the recommendations in the FAA 

policy memo ANM-112-08-002. 

The ANM-112-08-002 FAA policy memo provides the following alternate requirements: 

1. Instead of compliance with the requirements of § 25.981(a)(3), the applicant 

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 lightning-related ignition sources is provided for each area of the 

structural design area proposed to be exempt from the requirements of that 

regulation. 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) fuel tank vapor ignition because of that feature and all other non-faulttolerant features, when their fuel tank vapor ignition event probabilities are 

summed, is shown to be extremely improbable. 

2. The applicant 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. 

14 CFR 11.81 (d) Reason Why Granting Relief Would be In Public Interest 

Public Interest

Embraer has used state-of-art design practices and techniques to provide an adequate 

level of safety, and all practical measures have been implemented in the design. In 

search of compliance with the requirement, additional features to comply with the third 

layer of protection have been considered, but were concluded to be impractical. 

Adoption of the third layer would lead to significant impacts in weight, cost, 

manufacturing and maintenance, with no correspondent increase in safety levels. 

Additional protection features could make more difficult to perform fuel tank inspections. 

Increased frequency of inspection could lead to damage to internal tank components 

and structure, as well as to the lightning protection features. 

Requiring the EMB-550 to attempt to directly comply with this rule would prevent 

Embraer to complete the design and certify the aircraft on a competitive schedule. It 

would also render the EMB-550 to be of lesser value to the public interest with no 

commensurate increase in safety. 
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EMB-550 has state-of-the-art design solutions implemented on the fuel tanks which 

comply with § 25.954 and SFAR 88 requirements. Embraer considers that the solutions 

implemented on EMB-550 have an adequate level of safety and considers a grant of 

exemption applicable for this aircraft. 

Therefore, Embraer believes that it is in the public interest for the FAA to grant this 

exemption. 

14 CFR 11.81 (e) Reasons Why Exemption would Not Adversely Affect Safety 

Justification:

Effect of Exemption on Safety 

With current design practices for lightning protection, Embraer aircraft designs have 

accumulated in excess of 24 million revenue service flight hours with no lightning 

related events. The accident free fleet history shows current Embraer wing designs 

have sufficient protection against lightning induced fuel tank ignition events. 

This safety record for the fuel system designs upon which the EMB-550 design is 

based, indicates that the proposed fuel tank lightning protection design of the model 

EMB-550 will be safe. 

Proposed Risk Mitigation 

Embraer will submit detailed Proprietary information to the FAA about the measures 

taken in the EMB-550 design to provide practical structural lightning protection. In 

general, the EMB-550 lightning protection features are based on state of the art industry 

design practices for aluminum wing structure including inherently conductive low 

resistance current paths. These protection features have been used in existing inservice designs. 

EMB-550 is being designed considering the following mitigation means: 

- reduction of likelihood of flammable vapors, and 

- prevention of ignition sources. 

Reduction of likelihood of flammable vapors will be complied with considering 

flammability standards of fuel tank Fleet Average Flammability Exposure on an airplane 

not exceeding three percent of the Flammability Exposure Evaluation Time (FEET) as 

defined in Appendix N of part 25, or that of a conventional unheated aluminum wing fuel 

tank in the airplane model being evaluated, whichever is greater. 
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The fuel tanks are designed to have continuous ventilation during flight and to be far 

from aircraft heat sources. 

Ignition prevention due to lightning strikes is analyzed according to the guidelines 

established by FAA policy memo ANM 112-08-002. 

Embraer proposes to enhance the lightning protection by incorporating additional faulttolerant protection for fasteners in areas of potential swept lightning attachment 

(referred to as Zone 2) by sealing the fasteners to contain the products of a possible 

spark in the event that the primary protective features fail, thereby increasing the level 

of fuel tank safety. 

Embraer will show that the structural fastener design of the EMB-550 wing will have two 

reliable and effective features for lightning protection. Testing will show that the fastener 

installation will be safe for applicable lightning zone requirements and will not produce 

any sparks inside the fuel tanks. Additionally, Embraer will use the application of 

sealant, as a second layer of protection, to contain a spark should one occur from a 

failed fastener. For the limited areas in which a single failure of a fastener could result in 

loss of both protection features, or any other area where a single layer of protection is 

all that can practically be provided, a safety assessment will be performed to show that 

the probability of a lightning related fuel tank ignition event is extremely improbable. The 

systems supporting structure will also be analyzed as part of the fault tree assessment 

to ensure that they meet the requirements in the policy memo. For fault-tolerant joint 

types, it will be demonstrated the independence of the two protective features already 

considered in the design of EMB-550 fuel tanks. For Non-Fault-Tolerant joint types, 

numerical probability assessment is performed to verify probability of fuel-vapor ignition 

and demonstrate that it is extremely improbable. 

Embraer will verify that manufacturing quality and control is adequately performed and 

maintenance procedures consider CDCCL for fuel-system and fuel-tank structure. 

Additionally, Embraer will utilize production procedures in order to minimize the risk of 

mis-installed protective measures, and to identify and repair errors in such a way that 

the lightning protection features will be maintained. The instructions for continued 

airworthiness and repair procedures will also be provided to ensure the protection 

features are maintained throughout the life of the airplane. 

Verification of the low level of flammability exposure, and the analysis and tests to be 

performed for the protection features failure modes identified on the fuel tank structure 

will show that the EMB-550 has an adequate level of safety, even with the absence of 

the third independent layer of protection. 
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14 CFR 11.81 (f) Summary For Publication In Federal Register 

Embraer requests an Exemption from 14 CFR 25.981(a)(3) Amdt. 25-102 for fuel tank 

structural lightning protection in the EMB-550 aircraft. 

14 CFR 11.81 (g) Additional Information to Support Request 

Exemption No 10.138 (Regulatory Docket No FAA-2009-1206). This exemption is 

provided as evidence that the FAA has previously granted exemption from the same 

regulation for another Embraer aircraft, on the matter of fuel tank structure lightning 

protection. 

Conclusions

Embraer is petitioning for an exemption for 14 CFR 25.981(a)(3) at amendment 102 for 

fuel tank structural lightning protection. 

Granting this exemption will allow Embraer to complete its design and certify the EMB550 for delivery. 

The proposed design for the EMB-550 will provide an appropriate level of safety against 

lightning induced fuel tank ignition, and will be shown to comply with the alternative 

requirements established in the FAA policy memo ANM-112-08-002.