A proposal to amend part 39 of the Federal Aviation Regulations to include an AD that applies to certain Twin Commander Models 500S and 690B airplanes was published in the Federal Register on June 30, 1993 (58 FR 34957). The action proposed to require removing a sample of the spar cap material for examination, and, depending upon the results of the examination, inspecting or replacing the spar cap. The proposed inspections would be accomplished in accordance with Twin Commander SB No. 215, dated March 3, 1992. The proposed replacements, if necessary, would be accomplished in accordance with one of the following, as applicable:
Twin Commander Custom Kit No. CK-144, Revision A, dated November 12, 1992, which applies to Twin Commander Model 690B airplanes;
Twin Commander Custom Kit No. CK-145, dated August 21, 1992, which applies to Twin Commander Model 500S airplanes; or
AVIADESIGN, Inc. Supplemental Type Certificate (STC), dated July 16, 1992,which applies to Twin Commander Model 690B airplanes.
Of the 80 affected airplanes registered in the United States, 34 have already accomplished this inspection in accordance with Twin Commander SB No. 215, dated March 3, 1992. For five of these airplanes, or approximately 15 percent, the examination revealed a grain structure that would require spar cap replacement under the criteria of this proposed AD. These five airplane operators voluntarily replaced the spar cap in order to assure safety of their airplane.
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.
Eight commenters concur with the proposed rule as written.
One commenter recommends deleting the terms "fine equi-axed" and "unusual cap grain structure" from the proposal. This commenter states that there is no standard for grain structure in aluminum alloy products and believes that characterizing the spar cap grain structure as unusual is inappropriate and may not focus on the best course of corrective action. The commenter also states that the word fine in "fine equi-axed grain structure" is so imprecise that the structure is unable to be accurately measured. The FAA concurs that "unusual grain structure" could be inappropriate and has changed the wording in the final rule AD to "smaller than the large elongated grains, but not fine equi-axed". The FAA does not concur that the term "fine equi-axed" is imprecise because the FAA included in the proposal (NOTE 2) a definition of this term. In addition, the EMTEC Corporation, which is the laboratory conducting the metallurgical examinations, has established, with the FAA and Twin Commander, the acceptable grain structure size of the spar cap.
This commenter also states that the grain structure should not be the sole indicator of susceptibility to stress corrosion. The FAA concurs. The affected airplanes are also included in the applicability of the actions specified in Dockets No. 92-CE-38-AD and No. 92-CE-43-AD, which require other inspections of the spar cap. The proposed AD is unchanged as a result of this comment.
This same commenter also recommends consideration of other comprehensive corrective actions that deal with the impact of design and operating stress and sources of bi-metallic-initiated general corrosion. The FAA has determined that the current corrective action is one that will return the airplane to its original certification level of safety. The FAA will evaluate any detailed corrective action, and, if determined to provide an equivalent level of safety, will approve it as an alternative method of compliance to that portion of the required action. The proposed AD is unchanged as a result of this comment.
Another commenter, the Civil Aviation Authority of Australia (CAA), recommends that the FAA expand the range of serial numbers in the applicability and expand thespar cap replacement to include all unusual grain structures as well as fine equi-axed grain structures. The FAA has re-examined all information related to this subject and has determined that the airplanes manufactured with spars of fine equi-axed grain structure are limited to those manufactured between May 1978 and October 1979. The results of inspections received to date including those from the CAA verify this conclusion. The proposed AD is unchanged as a result of this comment.
After examining 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 the minor wording change and 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 80 airplanes in the U.S. registry will be affectedby this AD, that it will take approximately 15 workhours hours per airplane to accomplish the required action, and that the average labor rate is approximately $55 an hour. Parts cost approximately $32 per airplane, and the metallurgical inspection will cost approximately $150. Based on these figures, the total cost impact of this AD on U.S. operators is estimated to be $81,360. As previously discussed, 34 of the 80 affected airplanes have already accomplished the required actions. This reduces the cost impact of this AD upon U.S. operators to $56,392. The manufacturer will also incur the cost of the required metallurgical examination. The EMTEC Corporation will bill the manufacturer and send the results of the required inspection to the airplane owner/operator. This will further reduce the cost impact upon U.S. operators by $8,400 from $56,392 to $47,992.
In addition, if the required examination reveals a fine equi-axed grain structure, replacing the spar cap will be required at a cost of approximately $100,000, parts and labor included. If the required examination reveals an unusual grain structure that was not a fine equi-axed structure, inspecting the spar cap for stress corrosion will be required at a cost of approximately $2,750 (50 workhours at $55 per hour). An airplane affected by this AD could have a compliance cost as low as $1,007 if the spar cap was found acceptable during the metallurgical examination, and as high as approximately $100,857 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 a metallurgical examination is necessary: $1,007 - $150 (cost incurred by manufacturer) = $857 X 0.8145 (capital recovery factor at an interest rate of 7 percent) = $70 annualized cost; or
If replacing the spar cap is necessary: approximately $100,857 X 0.8145 (capital recovery factor at an interest rate of 7 percent) = $8,215 annualized cost.
The required AD's from Dockets No. 92-CE-38-AD (for Model 690B), No. 92-CE-43-AD (for Model 500S), and No. 92-CE-58-AD (for both Models 500S and 690B) also affect certain airplanes included in this AD. The compliance costs of these other AD's add to the cost discussed above. However, replacing the spar cap is only required once, so the $100,000 replacement cost, if required, would be 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.
Of the 56 U.S.-registered airplanes affected by this AD that have not complied with Twin Commander SB No. 215, dated March 3, 1992, no owner owns more than one. Of these 56 different owners, 50 are businesses, not-for-profit enterprises, or state or local governments; and six are individuals.
The FAA cannot determine the sizes of all the 50 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 proposal will 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 alternativesto 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 achieve the 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: