## Petition for Partial Exemption Gulfstream Aerospace Corporation Lightning Protection of Fuel Tank Structure

14 CFR 25.981(a)(3)

Relief from section 14 CFR Part 25.981(a)(3) Amdt. 25-102

Gulfstream Aerospace Corporation (Gulfstream) of Savannah, Georgia has submitted an application to the FAA’s Atlanta Aircraft Certification Office for type certification of a new, twin-engine, transport category aircraft to be known as the Gulfstream model GVI. FAA Project Number TC8700AT-T has been assigned to this effort.

14 CFR section 25.981(a)(3), Amendment 25-102 requires that “(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.”

The FAA has issued Policy Memorandum AN M-112-08-002 to address the impracticality of compliance to 14 CFR 25.981(a)(3) Amendment 25-102 with regards to structural lightning protection. This policy provides guidance for applicants to obtain a partial exemption through meeting alternate requirem ents. The alternate requirements are as

follows:

1. Instead of compliance with the requirements of 14 CFR 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 of the 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.

After consideration of the FAA policy and review of the Model GVI design, Gulfstream has determined that compliance with 14 CFR 25.981(a)(3) for certain structural lightningprotection features is impractical. In accordance with the provisions of 14 CFR 11.81, and the guidance of FAA Policy Memorandum ANM-112-08-02, Gulfstream requests a partial exemption for certain aspects of 14 CFR 25.981(a)(3) at Amendment 25-102. Granting this partial exemption would permit type certification of the Gulfstream Model

GVI.

Discussion
The Model GVI is a new, twin-engine, transpor t category aircraft. The fuel storage system is a two-tank system. Each fuel tank is located in the respective left or right wing with each dedicated to its respective engine. The wing of the Model GVI is of a traditional metal structure. There are no other fuel tanks present in the aircraft.

14 CFR 25.981(a)(3) requires in part that the design ensures 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.

Gulfstream fully intended for all aspects of the Model GVI fuel tank to comply with the requirements of 14 CFR 25.981(a)(3). However, Gulfstream has concluded that compliance to 14 CFR 25.981(a)(3) for fuel tank structural fastener lightning protection is not practical. It is the latent nature of the potential failures associated with structural elements that make compliance impractical. Gulfstream is not aware of any feature or system that could be installed that would monitor and notify the pilot in the event of a failure of structural lightning protection features. Physical inspections are the only means to determine the continuity of these protection features. However, the fasteners and the associated lightning protection features are internal to and integral to the aircraft structure and therefore these inspections require access to the fuel tank. While reducing these inspection intervals would reduce exposure of the latent nature of the associated failure modes, it could also potentially introduce damage to the lightning protection features, damage to other components within the wing, or introduce foreign object debris into the wing.

Proposed Risk Mitigation

In accordan ce with FAA Policy Memorandum ANM-112-08-002, Gulfstream will submit detailed information to the FAA about the measures taken in the GVI design to provide practical structural lightning protection. In general the information provided will demonstrate that the GVI utilizes state of the art design and manufacturing techniques that ensure inherently conductive, low resistance, current paths. Gulfstream will enhance these protection features in areas of potential direct attachment of lightning strikes and swept lightning current by over-coating the fasteners with a protective layer

of fuel tank sealant.

Gulfstream will demonstrate that the GVI design meets the requirements outlined in ANM-112-08-002 by submitting the following:

1. A design assessment of the fuel tank structure to document lightning strike protection features and safety analysis of any structural areas not fully compliant with 14 CFR 25.981(a)(3). (GVI-GER-0127).

2. Identification of failures that could cause fuel vapor ignition (GVI-GER-0127).3. Laboratory Lightning Strike Testing to demonstrate that fastener installations will be safe for the applicable lightning zone.

4. Laboratory Lightning Strike Testing to demonstrate that a second layer of protection will contain a spark should one occur from a failed fastener.

5. Where a single layer of protection is all that can be practically provided, a safety assessment will be completed to demonstrate that the probability of alightning related fuel tank ignition event is extremely improbable (GVI-GER0127).

6. Review of manufacturing and quality control processes to minimize the risk of incorrectly installed protective measures.

7. Inspection intervals and criteria, and repair procedures included in the Instructions for continued airworthiness to ensure that the protection features are maintained throughout the life of the airplane.

Applicability

Gulfstream requests this partial exemption to 14 CFR 25.981(a)(3) for st ructural aspects of Fuel Tank Lightning Protection to be applicable to all Gulfstream Model GVI aircraft and derivatives after the date of this granting.

Issue of Public Interest

Gulfstream Aerospace Corporation designs, develops, manufactures, markets and services the world's most technologically advanced business jet aircraft to an international market. Gulfstream’s leadership position in the global business jet market is due to the efforts of its nearly eight thousand employees in the manufacturing plants, completion centers, and service centers across North America. The corporation utilizes numerous products, such as avionics and envir onmental control systems, from scores of suppliers located through out the United States. Gulfstream competes for new business all over the world. This partial exemption will directly impact the ability to certify the Gulfstream Model GVI aircraft thereby having a direct effect on Gulfstream aircraft sales. The manufacture, completion, and support of aircraft aids in the stabilization of the job market and fosters growth in the American economy. Steady employment and a healthy economy are certainly in the interest of the public.

As stated in FAA Policy Memorandum ANM-112-08-002, both the FAA and industry have determined that compliance with the current regulatory standards for these types of features is impractical. Gulfstream believes the proposal made herein is consistent with the expectations defined by the FAA in their policy. Requiring the Model GVI to comply with this rule would prevent Gulfstream from certifying the aircraft on a timely and competitive schedule, putting it in an unfair di sadvantage to its competitors. Finally, it will delay the benefit of other safety features introduced by this product and advancements in fuel efficiency. Increasing safety and a healthy environment are certainly in the interest of the public.

Effect of the Partial Exemption on Safety

This partial exemption inherently implies a somewhat greater hazard than full compliance with 14 CFR 25.981(a)(3). However, the alternate standards defined by ANM-112-08-002 are intended to ensure an appropriate level of safety taking intoconsideration the current state of the art design and manufacturing techniques. Further, when one considers all aspects of fuel tank flammability reduction for which the GVI is compliant, combined with the protection measures that are implemented and the corresponding safety analyses performed, granting this partial exemption will not adversely affect safety.

Waiver of Notice and Public Procedure

Gulfstream respectfully requests that , and believes that good cause exists why; action on this petition should not be delayed by publication and comment procedures. In addition, Gulfstream requests that the 120 day FAA review and processing period specified in 14 CFR 11.63 (d) be reduced to 60 days. Gulfstream feels this request is appropriate because this request does not set a precedent, the relief requested herein is similar to partial exemptions granted previous ly, and is made in full consideration of FAA Policy Memorandum ANM-112-08-002.

Operation Outside of the United States

In accordan ce with the provisions of 14 CFR 11.83, Gulfstream requests that this partial exemption be extended for operation outside of the United States. Gulfstream aircraft are routinely registered and operated outside of the United States and projections are the same for the Model GVI. Gulfstream believes that limiting this partial exemption to use within the United States would put Gulfstream at an unfair restriction on the marketability of this aircraft.

Conclusion

Gulfstream believes tha t the above arguments fa vor a grant of partial exemption from 14 CFR 25.981(a)(3). The proposed design for the GVI fuel system will provide an appropriate level of protection against lightning induced fuel tank ignition, and will be shown to comply with the alternative requirements provided in FAA Policy Memorandum ANM-112-08-002. Thus, Gulfstream believes it is in the public interest to allow this partial exemption and permit Gulfstream to move forward with the certification of the

Model GVI.