Transport Airplane Directorate 1601 Lind Ave, SW. Renton, Washington 98057-3356

March 24, 2011

Mr. Anthony Beck

Gulfstream

P.O. Box 2206 Savannah, GA 31402-2206

Dear Mr. Beck:

We have reviewed your petition for exemption (Docket No. FAA-2010-1119) and determined that we require more informa tion before we can continue processing your petition. In that letter, y ou requested partial exemption from the requirements of § 25.981(a)(3) of Title 14 of Code of Federa l Regulations (14 CFR) for the Gulfstream Model GVI airplane that is currently being evaluated for FAA type certification. The exemption, if granted, would permit relief from the requirements of fuel tank structural lightning protection. In support of your petiti on, you submitted a report titled “Structural Assessment for Fuel Systems Lightning Prot ection Certification for FAA 14 CFR 25.981,”

Document No. GVI-GER-0127. Review of the supporting report i ndicates additional information is needed for our office to process your request for exemption.

The fault tree analysis provided in your report does not identify any si ngle failures that could result in ignition sources being present in the fuel tanks. Du ring review of industry data,

several failure modes have been identified that can defeat faul t tolerant designs. Examples include structural cracking, as we ll as fastener failures that ca n cause loss of sealant, which is the secondary ignition prevention feature. The GVI fuel tank construction and materials are similar to those used in other designs wh ere non-fault tolerant features have been identified. Therefore, the petition for exem ption or report should ei ther be revised to identify these features, or Gulfstream should submit data substantiating that these failures are not possible on the Model GVI airplane.

Your petition states that, after cons idering FAA Policy Memo ANM-112-08-002 and reviewing the Model GVI desi gn, Gulfstream has determined that compliance with § 25.981(a)(3) for certain structural light ning is impractical. FAA Policy Memo ANM-112-08-002, however, requires petitioners s eeking an exemption under this policy to substantiate the practicality of eliminating any non-fault tolerant design features. While you did not identify any non-fault tolerant features , if any are identified as noted above, please provide detailed information a nd analyses of the practicalit y assessment that you conducted

to address the criteria as follows:

“. . . The petitioner should show that all pract ical measures have been taken to meet the requirements of § 25.981(a)(3) for the fuel tank structure. For the design features for which an exemption is sought, the petitione r should show what potentially compliant design changes were examined, and what design changes were ruled out based on impracticality.”2

In addition, please submit detailed informati on and analyses, as follows, to support your request for an exemption:

1. The analysis should show that the design, manufacturing processes, and

airworthiness limitations section of the in structions for con tinued airworthiness include all practical measures to preven t, and detect and correct, failures of structural lightning protection features because of manufacturing variability, aging, wear, corrosion, and likely damage.

2. The report addresses the basic fasteners used in the wing st ructure and briefly addresses the fuel access doors. However, the report does not address other detailed structural design features that could also require specific lightning protection. For example, those features coul d include fuel vents, fuel filler caps, pump housings, wing-to-body structural a ttachments, and flap /slat/aileron hinge fittings that could have fasteners that exte nd into the fuel tank structural supports and brackets for fuel and hydraulic tubes.

3. The report does not describe Gulfstream’s te sting plans in order to demonstrate that the design provides redundant a nd effective lightning protection.

4. The assumed failure rate for fasteners in the analysis is in the range of 10 -9

. Industry experience shows fastener failures do occur; therefore, th is rate appears to be overly optimistic. Additional substantiation for the assumption should be

submitted.

5. The discussion in section 5.6.1 states th at: “Sealing and corrosion protection aspects of the assembly process ensure s no aging effects due to corrosion which could jeopardize fastener bonding.” If this st atement is intended to indicate that the analysis is based upon no corrosion for the life of the GVI airplane, additional substantiation for this assumption should be submitted.

6. The analysis indicates qualit y assurance is dependent upon detecting fuel leakage.

Additional information should be submitte d on any limitation for dispatch of the airplane with fuel leakage present.

With regard to item 1, your petition disc ussed manufacturing cont rols for robotically

installed fasteners but it did not specifically address inspec tion of any non-fault tolerant design features. We request confirmation that any non-fault tolerant design features will receive 100% post-assembly inspection to validate that the features are present at the time of manufacture. Further, you identified an in spection interval in the analysis document; we also request confirmation that these periodic inspections of all ignition prevention features, as well as non-fault tolerant features will be identified as critical design configuration control limitations (CDCCLs).3

If you would like us to further process your pe tition, please send the information described above within 30 days. If we do not hear from you within 30 days, we will close the docket without notifying you any further. If you have any questions or require additional time, please contact Mike Dostert, (425) 227-2132, mike.dostert@faa.gov

/s/

Victor Wicklund Manager, Propulsion & Mechanical Systems, ANM-112 Transport Standards Staff Transport Airplane Directorate

Aircraft Certification Service