Airworthiness Directives; Short Brothers Model SD3-60, SD3-SHERPA, and SD3-60 SHERPA Series Airplanes

AGENCY:

Federal Aviation Administration (FAA), DOT.

ACTION:

Notice of proposed rulemaking (NPRM).

SUMMARY:

The FAA proposes to supersede an existing airworthiness directive (AD) for certain Short Brothers Model SD3-60, SD3-SHERPA, and SD3-60 SHERPA series airplanes. That AD currently requires a one-time inspection to detect cracks and/or corrosion of the gland nut on the shock absorber of the main landing gear (MLG), and follow-on actions. That AD also requires repair or replacement of any cracked/corroded gland nut with a new nut. This proposed AD would add airplanes to the applicability; add repetitive inspections and corrective actions; and provide an optional action that would end the repetitive inspections. This proposed AD is prompted by reports of cracked aluminum alloy gland nuts that had been inspected previously using the existing AD. We are proposing this AD to prevent failure of the aluminum alloy gland nut on the MLG shock absorber, which could cause the MLG to collapse.

DATES:

We must receive comments on this proposed AD by August 23, 2004.

ADDRESSES:

Use one of the following addresses to submit comments on this proposed AD.

• DOT Docket Web site: Go to http://dms.dot.gov and follow the instructions for sending your comments electronically.
• Government-wide rulemaking Web site: Go to http://www.regulations.gov and follow the instructions for sending your comments electronically.
• Mail: Docket Management Facility; U.S. Department of Transportation, 400 Seventh Street SW., Nassif Building, room PL-401, Washington, DC 20590.

Fax: (202) 493-2251.

• Hand Delivery: room PL-401 on the plaza level of the Nassif Building, 400 Seventh Street SW., Washington, DC, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. You can get the service information identified in this proposed AD from Short Brothers, Airworthiness & Engineering Quality, P.O. Box 241, Airport Road, Belfast BT3 9DZ, Northern Ireland.

You may examine the contents of this AD docket on the Internet at http://dms.dot.gov , or at the Docket Management Facility, U.S. Department of Transportation, 400 Seventh Street SW., room PL-401, on the plaza level of the Nassif Building, Washington, DC.

FOR FURTHER INFORMATION CONTACT:

Todd Thompson, Aerospace Engineer, International Branch, ANM-116, FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington 98055-4056; telephone (425) 227-1175; fax (425) 227-1149.

SUPPLEMENTARY INFORMATION:

Docket Management System (DMS)

The FAA has implemented new procedures for maintaining AD dockets electronically. As of May 17, 2004, new AD actions are posted on DMS and assigned a docket number. We track each action and assign a corresponding directorate identifier. The DMS AD docket number is in the form “Docket No. FAA-2004-99999.” The Transport Airplane Directorate identifier is in the form “Directorate Identifier 2004-NM-999-AD.” Each DMS AD docket also lists the directorate identifier (“Old Docket Number”) as a cross-reference for searching purposes.

Comments Invited

We invite you to submit any written relevant data, views, or arguments regarding this proposed AD. Send your comments to an address listed under ADDRESSES. Include “Docket No. FAA-2004-18661; Directorate Identifier 2003-NM-273-AD” at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the proposed AD. We will consider all comments received by the closing date and may amend the proposed AD in light of those comments.

We will post all comments we receive, without change, to http://dms.dot.gov , including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this proposed AD. Using the search function of our docket Web site, anyone can find and read the comments in any of our dockets, including the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review the DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78), or you may visit http://dms.dot.gov .

We are reviewing the writing style we currently use in regulatory documents. We are interested in your comments on whether the style of this document is clear, and your suggestions to improve the clarity of our communications that affect you. You can get more information about plain language at http://www.faa.gov/language and http://www.plainlanguage.gov .

Examining the Docket

You may examine the AD docket in person at the Docket Management Facility office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Management Facility office (telephone (800) 647-5227) is located on the plaza level of the Nassif Building at the DOT street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after the DMS receives them.

Discussion

On October 18, 1996, we issued AD 96-22-09, amendment 39-9797 (61 FR 57311, November 6, 1996), for certain Short Brothers Model SD3-60 and SD3-SHERPA series airplanes. That AD requires a one-time inspection to detect cracks and/or corrosion of the gland nut on the shock absorber of the main landing gear (MLG), and follow-on actions. That AD also requires repair or replacement of any cracked/corroded gland nut with a new nut. That AD was prompted by a report indicating that, due to stress corrosion and cracking of the gland nut on the shock absorber, the MLG collapsed on an in-service airplane. We issued that AD to detect and correct such stress corrosion or cracking in a timely manner and consequent reduced structural integrity of the gland nut, which could result in separation of the shock absorber cylinder from the MLG shock absorber body and, consequently, lead to the collapse of the MLG during landing.

Actions Since Existing AD Was Issued

Since we issued AD 96-22-09, the Civil Aviation Authority (CAA), which is the airworthiness authority for the United Kingdom, notified us of cracked aluminum alloy gland nuts on the MLG shock absorber of a Short Brothers Model SD3-60 and an SD3-SHERPA series airplane. These airplanes had been inspected using AD 96-22-09. The cracks were caused by corrosion around the inner shoulder radius of the gland nut. This condition, if not corrected, could cause the aluminum alloy gland nut on the MLG shock absorber to fail. A failed gland nut could cause the MLG to collapse.

The gland nut that is installed on certain Short Brothers Model SD3-60 SHERPA series airplanes is almost identical to that on the Model SD3-60 and SD3-SHERPA series airplanes that had the cracked gland nuts. Therefore, the Model SD3-60 SHERPA series airplanes may be subject to the same unsafe condition that occurred on the Model SD3-60 and SD3-SHERPA series airplanes.

Relevant Service Information

Short Brothers has issued the following service bulletins:

• Service Bulletin SD360 SHERPA-32-1, dated June 30, 2003, for Model SD3-60 SHERPA series airplanes;
• Service Bulletin SD360-32-34, Revision 1, dated June 30, 2003, for Model SD3-60 series airplanes; and
• Service Bulletin SD3 SHERPA-32-2, Revision 1, dated June 30, 2003, for Model SD3-SHERPA series airplanes.

These service bulletins describe procedures for doing a detailed inspection for corrosion and/or cracks of the aluminum alloy gland nut, part number (P/N) 200920604, on the MLG shock absorber, and procedures for doing any necessary corrective actions. The corrective actions include the following:

• Repairing the gland nut if only corrosion is found. The repair involves machining the inner faces and radius of the gland nut to remove the corrosion. If the gland nut is machined to a certain limit and the corrosion has not been removed, the gland nut must be replaced with a new gland nut.
• Replacing the gland nut with a new aluminum alloy gland nut having the same part number if any cracking is found or if the repair does not remove the corrosion.

The Short Brothers service bulletins refer to Messier-Dowty Service Bulletin 32-78SD, Revision 1, dated December 9, 2002. This Messier-Dowty service bulletin gives additional information about how to do the inspection and corrective actions.

Accomplishing the actions specified in these service bulletins will address the unsafe condition adequately. The CAA mandated Short Brothers Service Bulletin SD360 SHERPA-32-1 and Messier-Dowty Service Bulletin 32-78SD, and issued British airworthiness directive 008-06-2003, to ensure the continued airworthiness of these airplanes in the United Kingdom.

The Short Brothers service bulletins also refer to Messier-Dowty Service Bulletin 32-80SD, dated August 31, 2000, which describes procedures for installing a new steel gland nut that has improved resistance to corrosion. Accomplishing this Messier-Dowty service bulletin eliminates the need to repeat the inspections described in the Short Brothers service bulletins.

FAA's Determination and Requirements of the Proposed AD

These airplane models are manufactured in the United Kingdom and are type certificated for operation in the United States under the provisions of section 21.29 of the Federal Aviation Regulations (14 CFR 21.29) and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, the CAA has kept the FAA informed of the situation described above. We have examined the CAA's findings, evaluated all pertinent information, and determined that AD action is necessary for airplanes of this type design that are certificated for operation in the United States.

Therefore, we are proposing to supersede AD 96-22-09 to continue to require a one-time inspection to detect cracks and/or corrosion of the gland nut on the shock absorber of the MLG, and follow-on actions. This proposed AD would also:

• Add airplanes to the applicability;
• Add repetitive inspections and corrective actions; and
• Provide an optional action that would end the repetitive inspections.

The proposed AD would require you to use the service information described previously to perform these actions, except as discussed under “Difference Between the Proposed AD and the British Airworthiness Directive.”

Difference Between the Proposed AD and the British Airworthiness Directive

The British airworthiness directive applies only to Short Brothers Model SD3-60 SHERPA series airplanes; however, the unsafe condition also exists on Short Brothers Model SD3-60 and SD3-SHERPA series airplanes. Therefore, this proposed AD would apply to any of these three airplane models with an aluminum alloy gland nut, P/N 200920604, on the MLG shock absorber. This difference has been coordinated with the CAA.

Change to Applicability of Existing AD

We have changed the way the airplane models are listed in the Applicability section of the proposed AD. This change identifies the airplane models as they are published in the most recent type certificate data sheet.

Additional Change to Existing AD

This proposed AD would retain all requirements of AD 96-22-09. Since AD 96-22-09 was issued, the AD format has been revised, and certain paragraphs have been rearranged. As a result, the corresponding paragraph identifiers have changed in this proposed AD, as listed in the following table:

Change to Labor Rate

We have reviewed the figures we have used over the past several years to calculate AD costs to operators. We have increased the labor rate used in these calculations from $60 per work hour to $65 per work hour. This new figure accounts for various inflationary costs in the airline industry. The cost information, below, reflects this increase in the hourly labor rate.

Costs of Compliance

The following table provides the estimated costs for U.S. operators to comply with this proposed AD.

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 proposed AD. 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, under the authority delegated to me by the Administrator, the FAA proposes to amend 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.