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 ANM-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 requirements. 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 lightning 
protection 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, transport 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 accordance 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 a 

lightning 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 structural 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 environmental 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 disadvantage 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 into 
consideration 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 previously, and is made in full consideration of FAA 

Policy Memorandum ANM-112-08-002. 

Operation Outside of the United States 

In accordance 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 that the above arguments favor 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.