AD 97-02-21

This amendment adopts a new airworthiness directive (AD), applicable to certain EMBRAER Model EMB-120 series airplanes, that requires repetitive inspections to detect cracks in the wing rib-to-skin support brackets (shear clips), and replacement of cracked brackets with new or serviceable brackets. This amendment also requires the eventual replacement of certain brackets with new brackets, which terminates the requirement for the inspections. This amendment is prompted by reports of cracks in certain wing rib-to-skin support brackets in both the lower and upper skin of the wings. The actions specified by this AD are intended to prevent cracking of those support brackets, which can subsequently lead to the loosening of the rivets in the wing skin, leakage of fuel through the rivet holes, and, ultimately, the reduction of the structural integrity of the wing.

Final rule

97-02-21 EMBRAER: Amendment 39-9906. Docket 95-NM-192-AD.
Applicability: Model EMB-120 airplanes, serial numbers 120001, 120003, 120004, and 120006 through 120304 inclusive; certificated in any category.

NOTE 1: This AD applies to each airplane identified in the preceding applicability provision, regardless of whether it has been otherwise modified, altered, or repaired in the area subject to the requirements of this AD. For airplanes that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (e) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent reduced wing structural integrity and fuel leakage of the wing due to cracking of wing rib-to-skin support brackets, accomplish the following:

NOTE 2: The term "fuel leakage" and "stain," as used throughout this AD, are used as they are defined and classified in Chapter 28, Fuel, of the Airplane Maintenance Manual (AMM).

(a) Within 10 days after the effective date of this AD: Perform a visual inspection of the wing skin along rib lines 15 and 16 to detect any fuel leakage other than a stain. Thereafter, repeat this inspection every 50 flight hours until the requirements of paragraph (d) of this AD are accomplished.

(b) As a result of the inspection required by paragraph (a) of this AD, accomplish either paragraph (b)(1) or (b)(2), as applicable:

(1) If fuel leakage is detected during any inspection required by paragraph (a) of this AD: Within 50 flights after detection of fuel leakage, perform an internal visualinspection to detect cracking of the wing rib-to-skin support brackets (shear clips) that connect the lower and upper wing skins to ribs 15 and 16, in accordance with the Accomplishment Instructions, PART I, of EMBRAER Service Bulletin 120-57-0031, dated July 6, 1995.

(2) If no fuel leakage is detected during any inspection required by paragraph (a) of this AD: At the applicable time specified in paragraph (b)(2)(i) through (b)(2)(iv) of this AD, perform an internal visual inspection to detect cracking of the wing rib-to-skin support brackets (shear clips) that connect the lower and upper wing skins to ribs 15 and 16, in accordance with the Accomplishment Instructions, PART I, of EMBRAER Service Bulletin 120-57-0031, dated July 6, 1995.

(i) For airplanes that have accumulated less than 4,000 total flight cycles as of the effective date of this AD: Inspect prior to the accumulation of 5,200 total flight cycles, or within 1,200 flight cycles after the effective date of this AD, whichever occurs later.

(ii) For airplanes that have accumulated 4,000 or more total flight cycles, but less than 8,000 total flight cycles as of the effective date of this AD: Inspect within 1,200 flight cycles after the effective date of this AD.

(iii) For airplanes that have accumulated 8,000 or more total flight cycles, but less than 12,000 total flight cycles as of the effective date of this AD: Inspect within 800 flight cycles after the effective date of this AD.

(iv) For airplanes that have accumulated 12,000 or more total flight cycles as of the effective date of this AD: Inspect within 400 flight cycles after the effective date of this AD.

(c) As a result of the internal visual inspection to detect cracking of the wing rib-to-skin support brackets (shear clips) that connect the lower and upper wing skins to ribs 15 and 16, as required by paragraph (b) of this AD, accomplish the actions specified in paragraph (c)(1), (c)(2), or (c)(3), as applicable:

(1) If no cracking is detected: Repeat that internal visual inspection thereafter at intervals not to exceed 1,200 flight cycles until the requirements of paragraph (d) of this AD are accomplished.

(2) If any cracking is detected in only one wing skin support bracket, and that cracking is more than half the length of the bracket; and if any cracking also is detected in up to two additional wing skin support brackets and that cracking is less than half the length of the bracket: Repeat that internal visual inspection thereafter at intervals not to exceed 400 flight cycles, until the requirements of paragraph (d) of this AD are accomplished.

(3) If any cracking is detected other than that specified in paragraph (c)(2) of this AD: Prior to further flight, replace any support bracket that is cracked beyond the limits specified in paragraph (c)(2) of this AD either with a new or serviceable bracket having the same part number, or with a "new style" bracket having a part number specified in paragraph 3.1. of EMBRAER Service Bulletin 120-57-0031, dated July 6, 1995. Following replacement and prior to further flight, perform an additional internal visual inspection to detect cracking of the support brackets that connect the wing skins to ribs 18, 19, 20, 21, and 22 in accordance with the EMBRAER service bulletin.

(i) If no cracking is found in the support brackets that connect the wing skins at ribs 18, 19, 20, 21, or 22: Repeat that internal visual inspection thereafter at intervals not to exceed 1,200 flight cycles until the requirements of paragraph (d) of this AD are accomplished.

(ii) If any cracking is found in the support brackets that connect the wing skins at ribs 18, 19, 20, 21, or 22: Prior to further flight, replace the cracked bracket with a new or serviceable bracket having the same part number; rib 18 may also be replaced with a "new style" bracket having a part number specified in paragraph 3.1. of the EMBRAER service bulletin.

(d) Within 2 years after the effective date of this AD: Replace all wing rib-to-skin support brackets of ribs 15, 16, and 18 with "new style" brackets having a part number specified in paragraph 3.1. of EMBRAER Service Bulletin 120-57-0031, dated July 6, 1995. Replacement procedures shall be accomplished in accordance with the Accomplishment Instructions, PART II, of that service bulletin. Prior to further flight following that replacement, perform a visual inspection to detect cracking of the wing skin support brackets of ribs 19, 20, 21, and 22. If any cracking is found, prior to further flight, replace the cracked bracket with a new or serviceable bracket having the same part number, in accordance with the EMBRAER service bulletin. Accomplishment of these actions constitutes terminating action for the requirements of this AD.

(e) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may beused if approved by the Manager, Atlanta Aircraft Certification Office (ACO), FAA, Small Airplane Directorate. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Atlanta ACO.

NOTE 3: Information concerning the existence of approved alternative methods of compliance with this AD, if any, may be obtained from the Atlanta ACO.

(f) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the airplane to a location where the requirements of this AD can be accomplished.

(g) The actions shall be done in accordance with EMBRAER Service Bulletin 120-57-0031, dated July 6, 1995. This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from Empresa Brasileira de Aeronautica, S.A. (EMBRAER), Sao Jose dos Campos - SP, Brazil. Copies may be inspected at the FAA, Transport Airplane Directorate, 1601 Lind Avenue, SW., Renton, Washington; or at the FAA, Atlanta Aircraft Certification Office, Small Airplane Directorate, Campus Building, 1701 Columbia Avenue, Suite 2-160, College Park, Georgia; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(h) This amendment becomes effective on March 3, 1997.

A proposal to amend part 39 of the Federal Aviation Regulations (14 CFR part 39) to include an airworthiness directive (AD) that is applicable to certain EMBRAER Model EMB-120 series airplanes was published in the Federal Register on April 24, 1996 (61 FR 17853). That action proposed to require repetitive inspections to detect cracks in the wing rib-to-skin support brackets (shear clips), and replacement of cracked brackets with new or serviceable brackets. That action also proposed to require the eventual replacement of certain brackets with new brackets, which would terminate the requirement for the inspections.

Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the single comment received.

Request to Delete Inspection Requirement
The only commenter, a U.S. operator, requests that the proposal be revised to delete the requirement to conduct repetitive inspections of the brackets. This commenter states that the subject area already is inspected by its flight crews on preflight inspections, and by its mechanics on daily inspections and line checks. The commenter considers that the need for the inspection requirement, and the extra paperwork that would be involved, cannot be justified by any data. This commenter, who operates 63 of the affected airplanes, indicates that it has analyzed the last 12 months of data on fuel leaks in its fleet; the data indicate that there have been 43 fuel leaks associated with leaking rivets, but there were no broken or cracked brackets found.

The FAA does not concur with the commenter s request. While this commenter specifically may not have found cracked brackets, there have been several cases reported by other operators in which fuel leaks caused by broken or cracked brackets were discovered on in-service airplanes. The FAA finds that the proposed inspection requirement will be effective in finding and addressing fuel leakage, and any associated cracking of a support bracket, well before more serious problems associated with these conditions could occur. The FAA also points out that operators may discontinue the inspections once the newly designed brackets are installed and follow-on actions are accomplished.

Request to Clarify "New" and "Old" Bracket Design
This same commenter requests clarification regarding the types of replacement brackets that are required to be installed. Specifically, the commenter questions whether it would be acceptable to install "old style" brackets as replacement parts in cases where no "new style" brackets are available.

The FAA concurs that clarification is necessary. If cracking is found in the brackets at ribs 15, 16, or 18, and the extent of the cracking necessitates replacement, operators may install either another new or serviceable "old style" bracket having the same part number; or a "new style" bracket, having a part number that isspecified in paragraph 3.1. of EMBRAER Service Bulletin 120-57-0031. However, terminating action consists of replacing those brackets at ribs 15, 16, and 18 with only the "new style" brackets.

On the other hand, if cracking is found in brackets at other rib locations (namely, ribs 19, 20, 21, and 22), only the "old style" brackets (same part number) are required to be installed as replacement parts at those locations.

The final rule has been revised to clarify these points.

Revision of Format of Final Rule
The format of the final rule has been revised somewhat to follow more closely the format of procedures as they are presented in the referenced EMBRAER Service Bulletin 120-57-0031, dated July 6, 1995. The FAA considers that this reformatting will help to clarify the required procedures for affected operators.

Conclusion
After careful review of the available data, including the comments noted above, the FAA has determined that air safety and the public interest require the adoption of the rule with the changes previously described. The FAA has determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD.

Cost Impact
The FAA estimates that 169 airplanes of U.S. registry will be affected by this AD.

It will take approximately 6 work hours per airplane to accomplish the required visual inspection for cracking, at an average labor rate of $60 per work hour. Based on these figures, the cost impact of the inspection action on U.S. operators is estimated to be $60,840, or $360 per airplane, per inspection cycle.

It will take approximately 56 work hours to accomplish the required replacement of support brackets, at an average labor rate of $60 per work hour. Required parts will cost approximately $1,000 per airplane. Based on these figures, the cost impact of the replacement action on U.S. operators is estimated to be $736,840, or $4,360 per airplane.

The cost impact figuresdiscussed above are based on assumptions that no operator has yet accomplished any of the requirements of this AD action, and that no operator would accomplish those actions in the future if this AD were not adopted.

Regulatory Impact
The regulations adopted herein will not have substantial direct effects 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. Therefore, in accordance with Executive Order 12612, it is determined that this final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment.

For the reasons discussed above, I certify that this action (1) is not a "significant regulatory action" under Executive Order 12866; (2) is not a "significant rule" under 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. A final evaluation has been prepared for this action and it is contained in the Rules Docket. A copy of it may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES."

List of Subjects in 14 CFR Part 39
Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety.

Adoption of the Amendment
Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration amends 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: