On June 17, 2002, while dropping retardant on a fire near Walker, California, a United States Department of Agriculture (USDA) Forest Service Model C-130A airplane was involved in an accident, resulting from the structural failure of the center wing. Investigation revealed fatigue cracking in the lower skin panels and stringers of the center wing. The cause of such fatigue cracking has been attributed to the age, time-in-service, and flight cycles of the airplane. Such fatigue cracking, if not detected and corrected, could result in structural failure of the wings and consequent loss of control of the airplane.
FAA's Determination
We have determined that extensive cracking (multiple-site damage (MSD)) of the left- and right-side lower skin panels of the center wing between wing stations 41.0 and 71.0 and the front and rear spars, is likely to occur on Lockheed C-130A airplanes, type certificated in the restricted category. Repetitive inspections of these areas are necessary to ensure that cracks will be detected, and corrective action taken, to preclude crack growth to a size that would create an unacceptable risk of structural failure.
MSD is characterized by the simultaneous presence, at multiple locations, of relatively small fatigue cracks that have the same geometry and stress level. The presence of MSD is usually an indicator of normal fatigue wearout, as opposed to any kind of an anomaly (e.g., material or manufacturing defect). The length of critical MSD cracks is typically much smaller than that of a single, isolated critical crack.
Based on the reports of cracking, we have determined that the repetitive inspections required by this AD will focus on fastener holes penetrating the lower skin panels and stringers of the center wing in the affected areas. Due to the nature of MSD cracking, the cracks that will need to be detected are very small, perhaps less than 0.10 inch in length. While inspection methodologiesexist that can be used to detect cracks of this size, we are currently unaware of any for Lockheed C- 130A airplanes, type certificated in the restricted category. Therefore, owners and operators must submit inspection procedures and repetitive inspection intervals to the Manager, Atlanta Aircraft Certification Office (ACO), FAA. The inspection procedures must be sufficiently reliable to determine the location and orientation of cracks that are very small, perhaps less than 0.10 inch in length. A potential inspection method would be to develop an inspection procedure using a bolt hole eddy current technique, develop a reference standard to calibrate the test instruments, and then use the developed inspection procedures and calibrated instruments to detect cracks. Other potential inspection methods include eddy current, eddy current arrays, and ultrasonic techniques. Certain types of inspections, such as a radiographic, are inadequate to detect small crack lengths. Because of the potential catastrophic nature of this cracking, the initial inspection must be performed within 4 days after the effective date of this AD.
Repetitive inspections must be performed at intervals that prevent crack growth from exceeding the minimum residual strength required to support ultimate load on the affected structure. These repetitive inspection intervals must be based on a damage tolerance assessment of the skin panels and stringers. Guidance for damage tolerance procedures may be found in Advisory Circular (AC) 25.571-1C, dated April 29, 1998.
If any crack is detected during any inspection, operators must replace the cracked part with a new part; or repair and inspect at new intervals based on a damage-tolerance assessment of the wing panels and stringers, per a method approved by the Atlanta ACO. The repair must include a damage tolerance assessment as noted above, in addition to analysis showing static strength capability in compliance with the certification basis of theairplane. In the case of the repair, determination of new inspection intervals based on a damage-tolerance assessment of the repaired wing panels and stringers is necessary, because the repair may alter the inspection intervals that are necessary in order to detect cracks before the structure fails. Conversely, in the case of a replacement with a new part, the inspection intervals that apply to the unrepaired structure continue to be applicable.
In addition, operators must report the results of inspections to the Atlanta ACO. As a minimum, the report must include the following information:
Airplane manufacturer's serial number(s);
Time-in-service of airplane;
Applicable type certificate data sheet;
Description of usage under which the restricted category was issued (see 14 CFR part 21.25(b));
Part numbers and time-in-service of damaged and undamaged parts; and
Diagram(s) showing the location and orientation of cracks, and if available, the length of cracks.Explanation of the Requirements of the Rule
Since an unsafe condition has been identified that is likely to exist or develop on other Lockheed C-130A airplanes, type certificated in the restricted category, this AD is being issued to detect and correct fatigue cracking in the left- and right-side lower skin panels and stringers of the center wing, which could result in structural failure of the wings and consequent loss of control of the airplane. This AD requires repetitive inspections to detect cracks at fastener holes in the left- and right-side lower skin panels and stringers of the center wing between wing stations 41.0 and 71.0; and replacement of any cracked part with a new part, or repair and inspections at new intervals. This AD also requires operators to submit a report of the inspection findings to the FAA.
Interim Action
This is considered to be interim action until final action is identified, at which time we may consider further rulemaking.
Determination of Rule's Effective Date
Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective in less than 30 days.
Comments Invited
Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this 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 under the caption ADDRESSES. All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed.
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 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 rule that might suggest a need to modify the 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 that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket.
Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this rule must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 2002-NM-235-AD." The postcard will be date stamped and returned to the commenter.
Regulatory Impact
The regulations adopted herein will 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. Therefore, it is determined that this final rule does not have federalism implications under Executive Order 13132.
The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and that it is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation underDOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, 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, 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: