E6-4050. Airworthiness Directives; Gulfstream Aerospace Corporation Model G-159 Airplanes

AGENCY:

Federal Aviation Administration (FAA), Department of Transportation (DOT).

ACTION:

Supplemental notice of proposed rulemaking; reopening of comment period.

SUMMARY:

The FAA is revising an earlier proposed airworthiness directive (AD), applicable to all Gulfstream Aerospace Corporation Model G-159 airplanes. The original NPRM would have required repetitive non-destructive testing inspections to detect corrosion of the skin of certain structural assemblies, and corrective action if necessary. The original NPRM also would have required x-ray and ultrasonic inspections to detect corrosion and cracking of the splicing of certain structural assemblies, and repair if necessary. The original NPRM resulted from reports that exfoliation corrosion had been found in the lower layer of the lower wing plank splices. This action revises the original NPRM by expanding the inspection areas to include the wing lower plank splices, ailerons, flaps, elevators, vertical and horizontal stabilizers, rudder, rudder trim tab, and aft lower fuselage from fuselage station (FS)559 to FS669. The actions specified by this new proposed AD are intended to detect and correct corrosion and cracking of the lower wing plank splices and spot-welded skins of certain structural assemblies, which could result in reduced controllability of the airplane. This action is intended to address the identified unsafe condition.

DATES:

Comments must be received by April 17, 2006.

ADDRESSES:

Submit comments in triplicate to the Federal Aviation Administration (FAA), Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 96-NM-143-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056. Comments may be inspected at this location between 9 a.m. and 3 p.m., Monday through Friday, except Federal holidays. Comments may be submitted via fax to [phone]. Comments may also be sent via the Internet using the following address: [e-mail]. Comments sent via fax or the Internet must contain “Docket No. 96-NM-143-AD” in the subject line and need not be submitted in triplicate. Comments sent via the Internet as attached electronic files must be formatted in Microsoft Word 97 or 2000 or ASCII text.

The service information referenced in the proposed rule may be obtained from Gulfstream Aerospace Corporation, P.O. Box 2206, Mail Station D-25, Savannah, Georgia 31402. This information may be examined at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Atlanta Aircraft Certification Office, One Crown Center, 1895 Phoenix Boulevard, suite 450, Atlanta, Georgia.

FOR FURTHER INFORMATION CONTACT:

Michael Cann, Aerospace Engineer, Airframe Branch, ACE-117A, FAA, Atlanta Aircraft Certification Office, One Crown Center, 1895 Phoenix Boulevard, suite 450, Atlanta, Georgia 30349; telephone [phone]; fax [phone].

SUPPLEMENTARY INFORMATION:

Comments Invited

Interested persons are invited to participate in the making of the proposed rule by submitting such written data, views, or arguments as they may desire. Communications shall identify the Rules Docket number and be submitted in triplicate to the address specified above. All communications received on or before the closing date for comments, specified above, will be considered before taking action on the proposed rule. The proposals contained in this action may be changed in light of the comments received.

Submit comments using the following format:

• Organize comments issue-by-issue. For example, discuss a request to change the compliance time and a request to change the service bulletin reference as two separate issues.
• For each issue, state what specific change to the proposed AD is being requested.
• Include justification (e.g., reasons or data) for each request.

Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the proposed rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report summarizing each FAA-public contact concerned with the substance of this proposal will be filed in the Rules Docket.

Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this action must submit a self-addressed, stamped postcard on which the following statement is made: “Comments to Docket Number 96-NM-143-AD.” The postcard will be date stamped and returned to the commenter.

Availability of NPRMs

Any person may obtain a copy of this NPRM by submitting a request to the FAA, Transport Airplane Directorate, ANM-114, Attention: Rules Docket No. 96-NM-143-AD, 1601 Lind Avenue, SW., Renton, Washington 98055-4056.

Discussion

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to add an airworthiness directive (AD), applicable to all Gulfstream Aerospace Corporation Model G-159 airplanes, was published as a notice of proposed rulemaking (NPRM) in the Federal Register on June 6, 2001 (66 FR 30343). That NPRM would have required repetitive non-destructive testing inspections to detect corrosion of the skin of certain structural assemblies, and corrective action if necessary. That NPRM also would have required x-ray and ultrasonic inspections to detect corrosion and cracking of the splicing of certain structural assemblies, and repair if necessary. That NPRM was prompted by reports that exfoliation corrosion had been found in the lower layer of the lower wing plank splices. That condition, if not corrected, could result in local instability failures of the wing under certain load conditions and result in degradation of wing capability.

Actions Since Issuance of Previous Proposal

Since the issuance of that NPRM, we have received additional reports indicating corrosion in a larger area of the wing than the area specified in the original NPRM. This condition, if not corrected, could cause cracking and corrosion of the lower wing plank splices and spot-welded skins of certain structural assemblies, which could result in reduced controllability of the airplane.

Relevant Customer Bulletin

Gulfstream Aerospace Corporation has issued Gulfstream GI Customer Bulletin (CB) 337B, including Appendix A, dated August 17, 2005. The procedures in the CB describe non-destructive testing (NDT) inspections for corrosion and cracking of spot-welded skins of the elevators, aileron, rudder and rudder trim tab, flaps, aft lower fuselage, and vertical and horizontal stabilizers. The procedures in the CB also describe NDT inspections (e.g., x-ray and ultrasonic) for exfoliation corrosion and cracking for wing plank splices from wing station (WS) 40 to WS 310. Additionally, the procedures in the CB describe performing an eddy current or fluorescent penetrant inspection for evaluating any prior blending in the riser areas. The procedures in the CB also specify that if the blend-out exceeds the repair drawing specifications, contact the manufacturer. The procedures in the CB also request operators to send a report to the manufacturer specifying inspection results. Additionally, Appendix A provides corrosion repair schemes for certain structural repair removal thresholds in accordance with certain drawing numbers.

Gulfstream has also issued Gulfstream Tool No. ST905-377, an x-ray negative that is used as a chart to define corrosion levels. The tool describes specific levels of corrosion and contains criteria for determining certain levels of corrosion (“light,” “moderate,” and “severe”).

Comments

We have considered the following comments on the original NPRM.

Requests To Revise the Cost Impact Section

Two commenters request that the estimate for the Cost Impact section of the original NPRM, which was based on 80 work hours, be increased to reflect a more realistic cost. One commenter states that it has received price quotes from shops that range from $11,000 to $19,000 to perform the actions proposed in the original NPRM. The other commenter states that it has completed the inspections (excluding the x-rays and ultrasonic inspections) proposed in the original NPRM. The operator advises that its actual cost for each inspection, not including incidental and access costs, was $18,000.

We agree that the estimated cost impact should be revised. Based on the latest information provided by the manufacturer in Gulfstream GI CB 337B, we estimate that the work hours necessary for the inspections proposed in this supplemental NPRM would be between 300 and 450 work hours, depending on how many spot-welded skins have been replaced with bonded skin panels. We have revised the Cost Impact section to reflect the increase of the estimated work hours.

Request To Revise Initial Compliance Time

One commenter requests that the initial compliance times be revised. The commenter requests that the initial compliance time for the requirements of paragraph (a) of the original NPRM be changed to 18 months from the last inspection of Gulfstream GI CB 337 (referenced in the original NPRM as the appropriate source of service information) or 9 months from the effective date of this AD, whichever is later. The commenter states that operators who are currently in compliance with Gulfstream GI CB 337 would still be required to re-inspect within 9 months after the effective date of the AD. The commenter advises that this would cause unnecessary cost and airplane downtime, since CB 337 has an 18-month inspection time.

We do not agree that, in this case, the initial inspections required by paragraphs (a) and (c) of this supplemental NPRM can be revised for the convenience of the operators. The inspection areas have been expanded since the issuance of the original proposed NPRM, which referenced the original issuance of Gulfstream GI CB 337, dated December 10, 1993, as the appropriate source of service information. The expanded inspection areas are specified in Gulfstream GI CB 337B, including Appendix A, dated August 17, 2005, which is referenced in this supplemental NPRM as the appropriate source of service information. Operators who have accomplished the inspections specified in earlier revisions of the CB, may request approval of an extension of the compliance time in accordance with paragraph (h) of the supplemental NPRM. The repetitive inspections remain at intervals not to exceed 18 months. No change is necessary to the supplemental NPRM in this regard.

Request Not To Expand the Inspection Area

One commenter requests that we do not expand the inspection area unless it can be shown that those expanded areas have been found to have corrosion. The commenter advises that it has been informed by the manufacturer that a revision to Gulfstream GI CB 337 is going to be issued with additional inspection areas of the wing plank. The commenter also states that it has not found corrosion in all of the areas specified in the original NPRM.

We do not agree. We have received several reports indicating that corrosion has occurred on the inspection areas discussed in this supplemental NPRM, including the wing planks. The source of corrosion was determined to be spot-welded skins for the flight controls and aft lower fuselage. Gulfstream GI CB 337B, as explained previously, describes the appropriate areas of inspection. We have determined that an unsafe condition exists and that Gulfstream GI CB 337B describes the methods of detection of corrosion and cracking, and correction if necessary. We have not changed the supplemental NPRM as a result of this request.

Request To Provide a Different Inspection Interval

That same commenter also requests that, if a sampling of airplanes indicates corrosion on other areas, those areas of inspection have a different inspection interval than the inboard wing.

We do not agree. The commenter did not provide a suggested “different inspection interval” or any technical justification for what a “different inspection interval” might be. However, under the provisions of paragraph (h) of the supplemental NPRM, we may approve requests for adjustments to the inspection interval if data are submitted to substantiate that such an adjustment would provide an acceptable level of safety. No change to the supplemental NPRM is necessary in this regard.

Request To Revise Compliance Times for Repairs

Two commenters request that the FAA allow more time to address repairs to the wing plank splices. The commenters also request that, if corrosion is seen on the x-ray, it may also be confirmed by another form of NDT, such as ultrasonic inspection. The commenters both point out that all the other inspection areas allow for either mild or moderate corrosion to be deferred. One of the commenters requests that the FAA allow a “trace” of corrosion in the wing plank splices to be re-inspected in 18 months to see if the suspect area has changed in size, shape, or density before any action must be taken. The commenter adds that it is a known fact in the x-ray industry that not all indications are corrosion, and the commenter quotes an Applied Technical Services report: “In some cases indications similar to those observed on the films provided for evaluation of the wing plank splices may actually be attributed to conditions other than corrosion.”

We do not agree. The loading conditions and magnitudes on the wing are different from the flight controls and the fuselage. “Trace” levels of corrosion on the flight controls and fuselage are not as critical as on the wing. No change to the supplemental NPRM is necessary in this regard.

Request To Extend the Repetitive Inspection Interval

One commenter requests that the repetitive inspection interval be changed from “at intervals not to exceed 18 months,” to “at intervals not to exceed 36 months.” The commenter notes that, although the first Gulfstream GI flew in August of 1958, there has never been a structural problem with the wing. The commenter also points out that, prior to 1994, there wasn't even a requirement to NDT the parts of the GI.

We do not agree with the commenter's request to extend the repetitive inspection interval. In developing an appropriate interval, we considered the safety implications, the service history of the airplane regarding corrosion of the wings, and normal maintenance schedules for timely accomplishment of the inspections. In light of these items, we have determined that a 18-month interval is appropriate. However, paragraph (h) of the supplemental NPRM provides affected operators the opportunity to apply for an adjustment of the repetitive inspection interval if the operator also presents data that justify the adjustment.

Request To Defer Certain Inspections

One commenter requests that an inspection compliance time of 12 years be provided for lower wing planks that have been replaced or reconditioned. The commenter states that the manufacturer has told the commenter that replaced or reconditioned lower wing planks shouldn't need to be inspected for 12 years.

We do agree that the inspection may be deferred for 12 years if the lower wing planks have been replaced with new lower wing planks. Since there is no actual definition for “reconditioned” in this case, we do not agree that the inspection may be deferred for 12 years if the lower wing planks have been “reconditioned.” However, under the provisions of paragraph (h) of this supplemental NPRM, operators may request an alternative method of compliance (AMOC) if data are submitted to substantiate that such an AMOC would provide an acceptable level of safety.

Changes to 14 CFR Part 39/Effect on the Proposed AD

On July 10, 2002, the FAA issued a new version of 14 CFR part 39 (67 FR 47997, July 22, 2002), which governs the FAA's airworthiness directives system. The regulation now includes material that relates to altered products, special flight permits, and alternative methods of compliance (AMOCs). These changes are reflected in this supplemental NPRM.

FAA's Determination and Proposed Requirements of the Supplemental NPRM

Certain changes discussed above expand the scope of the original NPRM; therefore, we have determined that it is necessary to reopen the comment period to provide additional opportunity for public comment on this supplemental NPRM.

Difference Between the CB and the Proposed AD

Operators should note that, although the Gulfstream CB does not specify certain corrective actions for levels of corrosion, this proposed AD would require shortened repetitive intervals for the NDT inspections based on certain levels of corrosion, or replacement of the corroded component with a serviceable component. Although the CB specifies certain one-time inspections, this supplemental NPRM would require repetitive inspections, since the nature of the unsafe condition (corrosion and cracking) may occur after a one-time inspection. This difference has been coordinated with the manufacturer.

Clarification of a Note in the CB

The Gulfstream CB includes a note in the Accomplishment Instructions to contact a Gulfstream Field Service Representative if technical assistance is required in accomplishing the CB. We have included Note 1 in this proposed AD to clarify that any deviation from the instructions provided in the CB must be approved as an alternative method of compliance under paragraph (h) of this AD.

Costs of Compliance

There are approximately 52 airplanes of the affected design in the worldwide fleet. The FAA estimates that 25 airplanes of U.S. registry would be affected by this proposed AD, that it would take approximately between 300 and 450 work hours per airplane, depending upon how many spot-welded skins have been replaced with bonded skin panels, to accomplish the proposed actions, and that the average labor rate is $65 per work hour. Based on these figures, the cost impact of the proposed AD on U.S. operators is estimated to be between $487,500 and $731,250, or between $19,500 and $29,250 per airplane.

The cost impact figure discussed above is based on assumptions that no operator has yet accomplished any of the proposed requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions.

Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority.

We are issuing this rulemaking under the authority described in subtitle VII, part A, subpart III, section 44701, “General requirements.” Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action.

Regulatory Findings

We have determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would not have a substantial direct effect on the States, on the relationship between the national Government and the States, or on the distribution of power and responsibilities among the various levels of government.

For the reasons discussed above, I certify that the proposed regulation:

1. Is not a “significant regulatory action” under Executive Order 12866;

2. Is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and

3. Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

We prepared a regulatory evaluation of the estimated costs to comply with this supplemental NPRM and placed it in the AD docket. See the ADDRESSES section for a location to examine the regulatory evaluation.

List of Subjects in 14 CFR Part 39

• Air transportation
• Aircraft
• Aviation safety
• Safety

The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows:

PART 39—AIRWORTHINESS DIRECTIVES

1. The authority citation for part 39 continues to read as follows:

Authority: 49 U.S.C. 106(g), 40113, 44701.

§ 39.13

[Amended]

2. Section 39.13 is amended by adding the following new airworthiness directive:

Gulfstream Aerospace Corporation: Docket 96-NM-143-AD.

Applicability: All Model G-159 airplanes, certificated in any category.

Compliance: Required as indicated, unless accomplished previously.

To detect and correct corrosion and cracking of the spot-welded skins of the lower wing plank splices and certain structural assemblies, which could result in reduced controllability of the airplane, accomplish the following:

Note 1:

A note in the Accomplishment Instructions of the Gulfstream customer bulletin instructs operators to contact Gulfstream if any difficulty is encountered in accomplishing the customer bulletin. However, any deviation from the instructions provided in the service bulletin must be approved as an alternative method of compliance (AMOC) under paragraph (h) of this AD.

Non-Destructive Testing Inspections of the Fuselage, Empennage, and Flight Controls

(a) Within 9 months after the effective date of this AD, perform a non-destructive test (NDT) to detect corrosion of the skins of the elevators, ailerons, rudder and rudder trim tab, flaps, aft lower fuselage, and vertical and horizontal stabilizers; in accordance with Gulfstream GI Customer Bulletin (CB) No. 337B, including Appendix A, dated August 17, 2005. The corrosion criteria must be determined by the Manager, Atlanta Aircraft Certification Office (ACO), FAA. Gulfstream Tool ST905-377 is also an acceptable method of determining the corrosion criteria.

(1) If no corrosion or cracking is detected, repeat the inspection thereafter at intervals not to exceed 18 months.

(2) If all corrosion is detected that meets the criteria of “light” or “mild” corrosion, repeat the NDT inspections of that component thereafter at intervals not to exceed 12 months.

(3) If any corrosion is detected that meets the criteria of “moderate” corrosion, repeat the NDT inspection of that component thereafter at intervals not to exceed 9 months.

(4) If any corrosion is detected that meets the criteria of “severe” corrosion, before further flight, replace the component with a serviceable component in accordance with the CB.

Existing Repairs

(b) If any existing repairs are found during the inspections required by paragraph (a) of this AD, before further flight, ensure that the repairs are in accordance with a method approved by the Manager, Atlanta ACO, FAA.

Inspections of the Lower Wing Plank

(c) Except as provided in paragraph (f) of this AD: Within 9 months after the effective date of this AD, perform NDT inspections to detect corrosion and cracking of the lower wing plank splices in accordance with Gulfstream GI CB 337B, including Appendix A, dated August 17, 2005.

(1) If no corrosion or cracking is detected, repeat the NDT inspection at intervals not to exceed 18 months.

(2) If any corrosion or cracking is detected, before further flight, perform all applicable investigative actions and corrective actions in accordance with the customer bulletin.

Repair Removal Threshold

(d) For repairs specified in Appendix A of Gulfstream GI CB 337B, dated August 17, 2005: Within 144 months after the date of the repair installation, remove the repaired component and replace it with a new or serviceable component, in accordance with Gulfstream GI CB 337B, including Appendix A, dated August 17, 2005.

Prior Blending in the Riser Areas

(e) If, during the performance of the inspections required by paragraph (c) or (f) of this AD, the inspection reveals that prior blending has been performed on the riser areas: Before further flight, perform an eddy current or fluorescent penetrant inspection, as applicable, to evaluate the blending, and accomplish appropriate corrective actions, in accordance with Gulfstream GI CB 337B, including Appendix A, dated August 17, 2005. If any blend-out is outside the limits specified in the CB, before further flight, repair in a manner approved by the Manager, Atlanta ACO.

For Airplanes With New Lower Wing Planks

(f) For airplanes with new lower wing planks, as defined by paragraphs (f)(1) and (f)(2) of this AD: Within 144 months after replacement of the lower wing planks with new lower wing planks, or within 9 months after the effective date of this AD, whichever occurs later, perform all of the actions, including any other related investigative actions and corrective actions, specified in paragraph (c) of this AD.

Reporting Requirement

(g) Within 30 days of performing the inspections required by this AD: Submit a report of inspection findings (both positive and negative) to Gulfstream Aerospace Corporation; Attention: Technical Operations—Mail Station D-10, P. O. Box 2206, Savannah, Georgia 31402-0080. Information collection requirements contained in this regulation have been approved by the Office of Management and Budget (OMB) under the provisions of the Paperwork Reduction Act of 1980 (44 U.S.C. 3501 et seq.) and have been assigned OMB Control Number 2120-0056.

Alternative Methods of Compliance

(h)(1) The Manager, Atlanta ACO, FAA, has the authority to approve AMOCs for this AD, if requested in accordance with the procedures found in 14 CFR 39.19.

(2) Before using any AMOC approved in accordance with § 39.19 on any airplane to which the AMOC applies, notify the appropriate principal inspector in the FAA Flight Standards Certificate Holding District Office.

Issued in Renton, Washington, on March 9, 2006.

Kalene C. Yanamura,

Acting Manager, Transport Airplane Directorate, Aircraft Certification Service.