A proposal to amend part 39 of the Federal Aviation Regulations to include an AD that would apply to certain Twin Commander Models 685, 690, 690A, and 690B airplanes was published in the Federal Register on June 30, 1993 (58 FR 34959). The proposed AD would require (1) modifying the wing ribs at Wing Station (WS) 39; (2) inspecting (one-time) the main spar lower cap and lower wing stringer No. 7 at WS 39 for cracks or corrosion; and (3) replacing the spar cap if any cracks are found and treating any corrosion found. The proposed inspections would be accomplished in accordance with the ACCOMPLISHMENT INSTRUCTIONS section of Twin Commander SB No. 211, Revision 1, dated July 7, 1992. Replacing the spar cap, if required, would be accomplished in accordance with Twin Commander Custom Kit 144, Revision A, dated November 12, 1992; or AVIADESIGN, Inc. Supplemental Type Certificate SA5740NM, dated July 16, 1992, as applicable.
Interested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the 10 comments received.
Five commenters concur with the proposal as written.
One commenter recommends excluding Model 685 airplanes that show no signs of corrosion based on the inspection required by AD 91-08-09. The commenter feels that the proposal is unreasonably burdensome to private aviation (i.e.,14 CFR part 91 operators) and should not be mandatory. The FAA does not concur. AD 91-08-09 requires inspecting for corrosion on the main wing spar lower cap, but the inspection procedure will not detect cracks in the wing front spar lower cap (spar cap). Even if the inspection required by AD 91-08-09 reveals corrosion, there is no assurance that cracks at WS 39 do not exist. The purpose of the proposal is to provide a way to detect and correct cracks at WS 39. The FAA has determined that these cracks or failures of the WS 39 wing rib can occur on airplanes in any type of operation, and that this action is the best course to achieve the safety objective of returning the airplane to its original certification level of safety. The proposed AD is unchanged as a result of this comment.
Another commenter, the Civil Aviation Authority of Australia (CAA), recommends replacing the wing spar cap before the next 500 hours time-in-service (TIS) if corrosion is found, instead of treating any corrosion found. The CAA states that, if a corroded spar is not replaced, then the small fatigue crack formed as a result of the corrosion will grow to weaken the spar to a level below its design strength. The FAA is currently conducting a study to determine the fatigue crack growth rates from irregular corroded surfaces. Part of this study includes the consideration of a replacement time period for spar caps found corroded. When this study is complete, the FAA will consider taking further AD action to cover this issue. The proposed AD is unchanged as a resultof this comment.
A third commenter states that the inspection should be repetitive. This is one of the items the FAA is considering in the current study to determine the fatigue crack growth rates from irregular corroded surfaces. When this study is complete, the FAA will consider taking further AD action to cover this issue. The proposed AD is unchanged as a result of this comment.
A fourth commenter requests a change in the compliance time from 50 hours TIS to 180 days. This commenter believes that there will be a jam of airplanes in service shops, causing a possible parts shortage or forcing airplane owners/operators to utilize less qualified shops in order to meet the deadline. The FAA does not concur. Twin Commander has assured the FAA that there are adequate parts available for all repairs that could be required. In addition, the FAA has determined that there is an adequate number of certified maintenance shops available to accomplish the actions on all airplanes within the proposed compliance time. The proposed AD is unchanged as a result of this comment.
A fifth commenter, the Twin Commander Aircraft Corporaton, requests that the preamble of the proposal change to reflect that, of the 13 airplanes reported to have cracked spar caps, 12 were examined in detail and none had cracks exceeding the specified limits. The FAA concurs, and, because the entire preamble of the proposal is not repeated in the final rule action, the FAA is so noting this fact.
After careful review of all available information including the comments referenced above, the FAA has determined that air safety and the public interest require the adoption of the rule as proposed except for minor editorial corrections. The FAA has determined that these minor corrections will not change the meaning of the AD nor add any additional burden upon the public than was already proposed.
The FAA estimates that 439 airplanes in the U.S. registry will be affected by thisAD, that it will take approximately 168 workhours per airplane to accomplish the required action, and that the average labor rate is approximately $55 an hour (total labor cost of $9,240 per airplane). Parts cost approximately $1,300 per airplane. Based on these figures, the total cost impact of this AD on U.S. operators is estimated to be $4,627,060 ($10,540 per airplane). As previously discussed, 89 of the 439 affected airplanes have already accomplished the required actions. This reduces the cost impact of this AD upon U.S. operators from $4,627,060 to $3,689,000.
In addition, if the required inspection reveals cracks or corrosion that exceeds a certain amount, replacing the spar cap will be required at a cost of approximately $100,000 per airplane, parts and labor included. An airplane affected by this AD could have a compliance cost as low as approximately $10,540 (labor + parts) if cracks or corrosion is not found during the inspection, and as high as approximately $110,540 (inspection and modification + spar cap replacement) if the operator replaces the spar cap.
Based on an expected average remaining operating life of 30 years per affected airplane, the annualized compliance cost would be:
-- If only inspecting the spar cap and wing rib at WS 39 and modifying at WS 39 are necessary: $10,540 X 0.8145 (capital recovery factor at a 7 percent interest rate) = $858 annualized cost; or
-- If replacing the spar cap is necessary: approximately $110,540 X 0.8145 (capital recovery factor at a 7 percent interest rate) = $9,003 annualized cost.
The required AD's from Dockets No. 92-CE-26-AD (for Model 690B) and No. 92-CE-58-AD (for Models 685, 690, 690A, and 690B) will also affect certain airplanes included in this AD. The compliance costs of these other AD's will add to the cost discussed above. However, replacing the spar cap will only be required once, so the $100,000 replacement cost, if required, is a one-time action.
The Regulatory Flexibility Act of 1980 (RFA) was enacted by Congress to ensure that small entities are not unnecessarily or disproportionally burdened by government regulations. The RFA requires government agencies to determine whether rules would have a "significant economic impact on a substantial number of small entities," and, in cases where they would, conduct a Regulatory Flexibility Analysis in which alternatives to the rule are considered. FAA Order 2100.14A, Regulatory Flexibility Criteria and Guidance, outlines FAA procedures and criteria for complying with the RFA. Small entities are defined as small businesses and small not-for-profit organizations that are independently owned and operated or airports operated by small governmental jurisdictions.
The 350 U.S.-registered airplanes affected by this AD that have not complied with Twin Commander SB No. 211, Revision 1, dated July 7, 1992, are owned according to the following breakdown: 60 by individuals, 2 by U.S. government agencies, 9 by states or local governments, and 279 by other entities. Twenty entities own more than one of the affected airplanes: one owns 7, one owns 5, another owns 4, and the other seventeen own 2 each.
The FAA cannot determine the sizes of all the affected non-individual owner entities nor the relative significance of the costs estimated above. Because of these uncertainties, no cost thresholds for significant economic impact can be reasonably determined. Based on the possibility that this AD could have a significant impact on a substantial number of small entities, the FAA conducted a regulatory flexibility analysis. A copy of this analysis may be obtained by contacting the Rules Docket at the location provided under the caption "ADDRESSES".
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 significant under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979) because of substantial public interest; and, (3) may have a significant economic impact on a substantial number of small entities. The FAA has conducted an Initial Regulatory Flexibility Determination and Analysis and has considered alternatives to this action that could minimize the impact on small entities. A copy of this analysis may be obtained by contacting the Rules Docket at the location provided under the caption "ADDRESSES". After careful consideration, the FAA has determined that the required action is the best course to achievethe safety objective of returning the airplane to its original certification level of safety.
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 14 CFR part 39 of the Federal Aviation Regulations as follows:
PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.
Section 39.13 - [AMENDED]
2. Section 39.13 is amended by adding the following new AD to read as follows: