On February 1, 2003, we received a report of an ECi cylinder head, part number (P/N) AEC65385, that separated from the barrel at the head-to-barrel junction. Since that report, we have received reports of 27 additional ECi cylinder heads that had the same condition. We also received reports of six cylinder heads that had a crack between the 9th and 10th head fin from the head-to-barrel junction. All of the reported separations and cracks were located between the ninth and tenth head fin from the head-to-barrel junction. All of the cracks started on the exhaust side of the head. The ECi cylinder head, P/N AEC65385, is part of ECi cylinder, P/N AEC631397. RAM Series III, IV, and VII reciprocating engines are the primary users of these cylinders. The RAM series engines are TCM TSIO-520-NB, -VB, and -WB engines that are modified by supplemental type certificate (STC) SE4327SW, STC SE09104SC, or STC SE09261SC for operation at 325 HP or greater. In addition, we approved the engine cylinders, ECi P/N AEC631397 for use on TCM models 520 and 550 series reciprocating engines under a Parts Manufacturer Approval (PMA). The Airmotive Engine Division of ECi holds the PMA. ECi markets the parts as ECi parts. \n\nResults of Manufacturer's Investigation \n\n\tAn investigation by ECi revealed that cylinder heads, P/N AEC65385, manufactured between September 1, 2002, and May 12, 2003, SNs 1044 through 7708, are susceptible to an over-hardened condition, which reduces the fatigue strength of the cylinder. It also increases the chance that the cylinder will crack. \n\nRelevant Service Information \n\n\tWe reviewed and approved the technical contents of RAM Aircraft Mandatory Service Bulletin (MSB) MSB2003-02, dated August 8, 2003, and ECi MSB S.I. No. 04-1, Revision 1, dated March 11, 2004, that describe procedures for identifying, inspecting, and replacing affected cylinders. \n\nDifferences Between This AD and the Service Information \n\n\tRAM Aircraft MSB MSB2003-02, dated August 8, 2003, requires replacing only the No. 6 cylinder, ECi P/N AEC631397, on RAM Series III, IV, and VII engines. ECi MSB S.I. No. 04-1, Revision 1, dated March 11, 2004, requires identifying the suspect cylinders on TCM models 520 and 550 engines and inspecting them for cracks. This AD requires replacing all cylinders, ECi P/N AEC631397, on all RAM Series III, IV, and VII engines; a\nd all TCM model 520, and 550 series engines. \n\nFAA's Determination and Requirements of This AD \n\n\tThe unsafe condition described previously is likely to exist or develop on other RAM Series III, IV, and VII engines; and TCM model 520, and 550 series engines of the same type design. We are issuing this AD to prevent loss of engine power due to cracks in the cylinder head and possible engine failure caused by separation of a cylinder head. This AD requires: \n\n\tPerforming a check to identify cylinders, ECi P/ N AEC631397, S/Ns 1044 through 7708, within 50 hours time-in-service afterthe effective date of this AD. and \n\n\tIf a cylinder has an affected P/N and SN, replacing the cylinder before further flight if it was not inspected at ECi. \n\n\nFAA's Determination of the Effective Date \n\n\tSince an unsafe condition exists that requires the immediate adoption of this AD, we have found that notice and opportunity for public comment before issuing this AD are impracticable, and that good cause exists for making this amendment effective in less than 30 days. \n\nComments Invited \n\n\tThis AD is a final rule that involves requirements affecting flight safety and was not preceded by notice and an opportunity for public comment; however, we invite you to submit any written relevant data, views, or arguments regarding this AD. Send your comments to an address listed under ADDRESSES. Include "AD Docket No. 2004-NE-07-AD" in the subject line of your comments. If you want us to acknowledge receipt of your mailed comments, send us a self-addressed, stamped postcard with thedocket number written on it; we will date-stamp your postcard and mail it back to you. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify it. If a person contacts us verbally, and that contact relates to a substantive part of this AD, we will summarize the contact and place the summary in the docket. We will consider all comments received by the closing date and may amend the AD in light of those comments. \n\n\tWe are reviewing the writing style we currently use in regulatory documents. We are interested in your comments on whether the style of this document is clear, and your suggestions to improve the clarity of our communications with you. You can get more information about plain language at http://www.faa.gov/language and http://www.plainlanguage.gov. \n\nExamining the AD Docket \n\n\tYou may examine the AD Docket (including any comments and service information), by appointment, between 8:00 a.m. and 4:30 p.m., Monday through Friday, except Federal holidays. See ADDRESSES for the location. \n\nRegulatory Findings \n\n\tWe have 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\n\tFor the reasons discussed above, I certify that the regulation: \n\n\t1. Is not a "significant regulatory action" under Executive Order 12866; \n\n\t2. Is not a "significant rule" under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and \n\n\t3. 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\n\tWe prepared a summary of the costs to comply with this AD and placed it in the AD Docket. You may get a copy of this summary by sending a request to us at the address listed under ADDRESSES. Include "AD Docket No. 2004-NE-07-AD" in your request. \n\nList of Subjects in 14 CFR Part 39 \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 Federal Aviation Administration amends part 39 of the Federal Aviation Regulations (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\tAuthority: 49 U.S.C. 106(g), 40113, 44701. \n\n§ 39.13 (Amended) \n\n2. The FAA amends § 39.13 by adding the following new airworthiness directive: