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 all Bombardier Model DHC-8-101, - 102, -103, -106, -201, -202, -301, -311, and -315 airplanes was published in the Federal Register on December 18, 2003 (68 FR \n70469). That action proposed to require a detailed inspection of the wing leading edge de-icer boots to determine if they comply with the patch size and/or patch number limits in the critical zone as defined in the aircraft maintenance manual; and corrective action, if necessary. \n\nComments \n\n\tInterested persons have been afforded an opportunity to participate in the making of this amendment. Due consideration has been given to the comments received. \n\nRequest To Reference New Temporary Revisions \n\n\tOne commenter, an airplane operator, states that the proposed rule requires inspections using limits that were published in the aircraft maintenance manual (AMM) in October 2001. The commenter notes that these limits have all been revised, and now all have revision dates in 2003. In addition, the commenter states that if the new limits are not included in the proposed rule, then operators would be required to find and re-insert the older data into the AMM, which would negate two years of progress in maintaining the leading edge de-icer boots. \n\n\tWe infer that the commenter is requesting that we use the revisions that were published in 2003. We partially agree with the commenter's request. We have not revised paragraph (a) of the final rule to include the new AMM revisions because another suggestion by the same commenter (see "Request to Insert Limits Directly Into Final Rule") makes including a reference to these revisions in that paragraph unnecessary. However, we have listed these revisions in new Table 3 of new paragraph (c)(3) of the final rule (see "Explanation of New Paragraph (c)(3) of the Final Rule"). In addition, because the requirements in the new revisions are less restrictive, those operators who have complied with the limits published in the 2001 revisions are still compliant with the intent of the final rule. Therefore, we have added new Table 4 and new paragraph (e) to the final rule that gives credit to operators who have accomplished the required actions in accordance with the 2001 revisions of the AMM. \n\nRequest To Insert Limits Directly Into Final Rule \n\n\tThe same commenter suggests that, rather than referencing the AMMs for the necessary limits in paragraph (a) of the proposed rule, the FAA insert the necessary limits directly into paragraph (a). The commenter states that the chapters of the AMM referenced in paragraph (a) of the proposed rule contain significantly more information than apply to the patch limits that affect the stall margin. The commenter further states that the limits can be addressed concisely and, therefore, proposes that we specify the actual acceptance criteria in the proposed rule. The commenter states that this would allow operators to revise the AMMs as necessary to provide current information, yet would still mandate the limits that are required. The commenter also suggests that if paragraph (a) is changed as suggested, all references to the AMM in the proposed rule be changed to refer to paragraph (a). \n\n\tWe agree with the commenter's request to change paragraph (a) of the final rule and all references to it in the final rule for the stated reasons. Paragraph (a) has been revised to more clearly define the term, "patch limits" and to specify those specific limits. Additionally, all references to the AMM have been changed to refer to paragraph (a). We also have revised the Summary of the final rule to remove the reference to the limits in the critical zone "as defined in the AMM." \n\nRequest To Allow Ferry Flights \n\n\tThe same commenter requests that we add a new paragraph to the final rule regarding ferry flights. The proposed paragraph would allow operators of any airplane that has de-icer boots that do not meet the AMM limits to ferry the airplane to a location where repairs can be made, provided the airplane is operated under the limits in Table 2 of the proposed rule. We infer that the operator would like the flexibility to move airplanes to convenient locations for repair without the need to request a special flight permit. \n\n\tWe partially agree with the commenter's request to add a paragraph regarding ferry flights to the final rule. On July 10, 2002, we issued a new version of 14 CFR part 39 (67 FR 47997, July 22, 2002), which governs the FAA's airworthiness directives system. The regulation now includes material that relates to special flight permits for ferry flights. As stated in 14 CFR 39.23: "(T)he operations specifications giving some operators authority to operate include a provision that allow(s) them to fly their aircraft to a repair facility to do the work required by an airworthiness directive. If you do not have this authority, the local Flight Standards District Office of FAA may issue you a special flight permit unless the airworthiness directive states otherwise. To ensure aviation safety, FAA may add special requirements for operating your aircraft to a place where the repairs or modifications can be accomplished. FAA may also decline to issue a special flight permit in particular cases if we determine you cannot move the aircraft safely." If an operator does not have the specified authority and requires a special flight permit, we will evaluate any request for a special flight permits on a case by case basis at the time of the request. We do not find it necessary to change the final rule in this regard. \n\nRequest To Address Varying Levels of Degradation \n\n\tAnother commenter is concerned about varying levels of degradation of the de-icer boots in the affected fleet of airplanes. The commenter states that there may be airplanes in operation that do not exceed the limits in the proposed rule, but still have leading edge de-icer boots that are in a state of repair that may degrade the aerodynamic performance of the wing more than other airplanes with less damage. \n\n\tWe infer that the commenter is requesting that we revise the proposed rule to address airplanes that carry varying levels of degradation. We do not agree. The limits in the final rule address the worst-case patch size and patch limits in the wing critical zone. In devising these limits, we assessed the amount of damage that is acceptable for safe flight without the performance penalties cited in Table 2 of this AD. These limits take into account the airplane aerodynamic characteristics and the smoothness of the boots. We have not changed the final rule in this regard. \n\nRequest To Clarify Applicability of Performance Penalties \n\n\tThe same commenter states that it is unclear if the performance penalties cited in Table 2 of the proposed rule are to be included only in the airplane flightmanuals (AFM) of airplanes that have boot patches that exceed the patch-number limits, or if the penalties will be applicable to all Model DHC-8 airplanes in a given operator's fleet until all of the proposed inspections and replacements are completed. \n\n\tFrom these statements, we infer that the commenter is requesting that we clarify the applicability of the performance penalties listed in Table 2 of the proposed rule. We do not agree that is necessary to change the applicability of the final rule to make this clarification. As stated in paragraph (c) of the final rule, the performance penalties apply only to airplanes that require corrective actions. Airplanes that require corrective actions are those \nthat have boot patches that exceed the limits specified in the AMM. We have not changed the final rule in this regard. However, we have clarified paragraphs (c) and (c)(1) of the final rule based on the addition of a new paragraph (c)(3) to the final rule. These changes are described below in "Explanation of New Paragraph (c)(3) of the Final Rule" and "Explanation of Clarifications Made in Paragraphs (c) and (c)(1) of the Final Rule." \n\nRequest To Reduce Compliance Time for Replacements \n\n\tThe same commenter requests that we reduce the 24-month compliance time replacing the wing de-icer boots, which is specified in paragraph (c)(2) of the proposed rule. The commenter states that a 24-month compliance time could allow some airplanes to be exposed to icing conditions for up to three icing seasons. \n\n\tWe do not agree with the request for a shorter compliance time in paragraph (c)(2) of the final rule. In developing the proposed compliance time, we considered the fact that there have been no occurrences of stall problems in the past, and that an airplane that requires corrective action is bound to the performance penalties in Table 2 of the final rule during this 24-month period. We determined that the compliance is appropriate in consideration of the safety implications, the average utilization rate of the affected fleet, the practical aspects of an orderly inspection of the fleet, and the availability of required modification parts. We have not changed the final rule in this regard. \n\nRequest for Ongoing Monitoring Program \n\n\tThe same commenter requests that there be a clearly delineated ongoing program included in the proposed rule to monitor the number and size of patches on the new boots in order to stay in compliance with AMM limits. The commenter is concerned that the proposed rule is not clear about how operators should monitor the number and size of boot patches on the new boots after replacement, and still stay in compliance with the AMM limits. \n\n\tWe do not agree that it is necessary to delineate a monitoring program. Paragraph (d) of the final rule states that "as of the effective date of this AD, no person may install--on any airplane--a de-icer boot patch in the critical zone of the wing de-icer boots that exceeds the patch limits specified in paragraph (b) of this AD." Paragraph (d) of this AD is intended to prevent the installation of any patches beyond the specified limits. Therefore, after the boot replacements have been made, it is unnecessary to institute an ongoing monitoring program. We have not changed the final rule in this regard. \n\nConclusion \n\n\tAfter careful review of the available data, including the comments noted above, we have determined that air safety and the public interest require the adoption of the rule with the changes described previously. We have determined that these changes will neither increase the economic burden on any operator nor increase the scope of the AD. \n\nExplanation of New Paragraph (c)(3) of the Final Rule \n\n\tParagraph (c)(3) of the final rule gives operators two methods to choose from for replacing the de-icer boots: \n\n\tIn accordance with a method approved by either the Manager, Systems and Flight Test Branch, ANE-172, FAA, New York Aircraft Certification Office; or \n\n\tIn accordance with a method approved by Transport Canada Civil Aviation (or its delegated agent). \n\n\tThe paragraph further states that the applicable chapter of the AMM referenced in Table 3 of paragraph (c)(3) of the final rule is "one approved method." \n\n\tWe find that allowing operators to accomplish the actions according to one of the cited methods will not impose additional burden for operators to comply with the actions in the AD. \n\nExplanation of Clarifications Made in Paragraphs (c) and (c)(1) of the Final Rule \n\n\tAdding paragraph (c)(3) to this final rule made it necessary to clarify the statements in paragraphs (c) and (c)(1) of the final rule. Paragraph (c) of the final rule now specifically requires operators of airplanes that require corrective actions to do the actions in paragraphs (c)(1) and (c)(2). Paragraph (c)(1) of the final rule now also refers to airplanes that have findings that exceed the patch limits in accordance with paragraph (b)(2) of the final rule. \n\nCost Impact \n\n\tWe estimate that 200 airplanes of U.S. registry will be affected by this AD, that it will take approximately 2 work hours per airplane to accomplish the required actions, and that the average labor rate is $65 per work hour. Based on these figures, the cost impact of the AD on U.S. operators is estimated to be $26,000, or $130 per airplane. \n\n\tThe cost impact figure discussed above is 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. The cost impact figures discussed in AD rulemaking actions represent only the time necessary to perform the specific actions actually required by the AD. These figures typically do not include incidental costs, such as the time required to gain access and close up, planning time, or time necessitated by other administrative actions. \n\nRegulatory Impact \n\n\tThe 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. \n\n\tFor 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. \n\nList of Subjects in14 CFR Part 39 \n\n\tAir transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. \n\nAdoption of the Amendment \n\n\tAccordingly, 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: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n\t1. The authority citation for part 39 continues to read as follows: \n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\nSec. 39.13 (Amended) \n\n\t2. Section 39.13 is amended by adding the following new airworthiness directive: