Discussion \n\n\n\tThe FAA received recent reports of cracks found in the wings of two RAC 1900D airplanes. During routine maintenance, the wing rear spar lower caps and rear spar web were found to have significant cracks. \n\tThe RAC Structural Inspection Manual requires a thorough inspection of the wing rear spar at 17,500 hours time-in-service (TIS) with repetitive inspections at intervals of 3,000 hours TIS. \n\tOne airplane had 19,126 hours TIS when cracks were found. The cracks were in the lower aft spar cap flange, but the cracks extended upward into the web and terminated at the lightening hole in the spar web. Fasteners were also found missing in the spar cap and wing cove splice plate. There were no discrepancies recorded from the initial inspection at 17,500 hours TIS on this airplane. \n\tEarly indications show similar cracking on the other airplane. We continue to gather information on this airplane. \n\tAnalysis shows that similar cracks could also develop in the wings of the Models 1900 and 1900C airplanes. \n\tCracking in the wing rear spar lower caps, if not corrected, could result in wing failure. Such a wing failure could result in the wing separating from the airplane with consequent loss of control. \n\tOn August 31, 2006, FAA issued emergency AD 2006-18-51 to require you to do a one-time visual inspection of both the left and right wing rear spar lower caps for cracking and other damage such as loose or missing fasteners; repair any cracks or damage found; and report any cracks or damage found to the FAA and RAC. \n\nFAA's Determination \n\n\n\tThe FAA determined that immediate corrective action was required, that notice and opportunity for prior public comment were impracticable and contrary to the public interest, and that good cause existed to make the AD effective immediately by individual letters issued on August 31, 2006, to all known U.S. operators of the affected RAC Models 1900, 1900C, and 1900D airplanes. Theseconditions still exist, and the AD is published in the Federal Register as an amendment to section 39.13 of the Federal Aviation Regulations (14 CFR 39.13) to make it effective to all persons. \n\nComments Invited \n\n\n\tThis AD is a final rule that involves requirements affecting flight safety, and we did not precede it by notice and an opportunity for public comment. We invite you to send any written relevant data, views, or arguments regarding this AD. Send your comments to an address listed under the ADDRESSES section. Include the docket number "FAA-2006- 25760; Directorate Identifier 2006-CE-48-AD" at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the AD. We will consider all comments received by the closing date and may amend the AD in light of those comments. \n\tWe will post all comments we receive, without change, to http://dms.dot.gov , including any personal information you provide. Wewill also post a report summarizing each substantive verbal contact we receive concerning this AD. \n\nAuthority for This Rulemaking \n\n\n\tTitle 49 of the United States Code specifies the FAA's authority to issue rules on aviation safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency's authority. \n\tWe are issuing this rulemaking under the authority described in Subtitle VII, Part A, Subpart III, Section 44701, "General requirements." Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action. \n\nRegulatory Findings \n\n\n\tWe determined that this AD will not have federalism implications under Executive Order 13132. This AD 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. \n\tFor the reasons discussed above, I certify that this AD: \n\t(1) Is not a "significant regulatory action" under Executive Order 12866; \n\t(2) Is not a "significant rule" under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and \n\t(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. \n\tWe prepared a regulatory evaluation of the estimated costs to comply with this AD and placed it in the AD docket. \n\nExamining the AD Docket \n\n\n\tYou may examine the AD docket that contains the AD, the regulatory evaluation, any comments received, and other information on the Internet at http://dms.dot.gov; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The Docket Office (telephone (800) 647-5227) is located at the street address stated in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt. \n\nList of Subjects in 14 CFR Part 39 \n\n\n\tAir transportation, Aircraft, Aviation safety, Safety. \n\nAdoption of the Amendment \n\nAccordingly, under the authority delegated to me by the Administrator, the FAA proposes to amend 14 CFR part 39 as follows: \n\nPART 39--AIRWORTHINESS DIRECTIVES \n\n1. The authority citation for part 39 continues to read as follows: \n\n\n\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n\n\nSec. 39.13 (Amended) \n\n2. The FAA amends Sec. 39.13 by adding the following new airworthiness directive (AD):