SUPPLEMENTARY INFORMATION:

Comments Invited

We invite you to send us any written relevant data, views, or arguments regarding this proposal. Send your comments to an address listed under ADDRESSES . Include “Docket No. FAA-2007-0051; Directorate Identifier 2007-NE-37-AD” in the subject line of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of the proposed AD. We will consider all comments received by the closing date and may amend the proposed AD in light of those comments.

We will post all comments we receive, without change, to http://www.regulations.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact with FAA personnel concerning this proposed AD. ( printed page 19773) Using the search function of the Web site, anyone can find and read the comments in any of our dockets, including, if provided, the name of the individual who sent the comment (or signed the comment on behalf of an association, business, labor union, etc.). You may review the DOT's complete Privacy Act Statement in the Federal Register published on April 11, 2000 (65 FR 19477-78).

Examining the AD Docket

You may examine the AD docket on the Internet at http://www.regulations.gov; or in person at the Docket Operations office between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this proposed AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Operations office (telephone (800) 647-5527) is the same as the Mail address provided in the ADDRESSES section. Comments will be available in the AD docket shortly after receipt.

Discussion

Superior Air Parts and operators in the field have reported 24 SAP cylinder assemblies with cracks or separation in the area of the exhaust valves. Some instances resulted in forced landings of the airplanes. The reported failures were cylinder assemblies in the naturally-aspirated and turbocharged engines. Most of the failures were on airplanes that have a high ratio of takeoffs and landings per flight hour. Most of the failures also occurred on airplanes that are operated predominantly at low altitude. SAP first informed us on July 12, 2006, that at least 14 SAP investment cast cylinder assemblies, P/Ns SA52000-A1, SA52000-A20P, SA52000-A21P, SA52000-A22P, SA52000-A23P, SA55000-A1, SA55000-A20P, had cracked in the area of the exhaust valve of the cylinder head since the year 2000. We received reports of 10 additional failures since that time, and the total number of reported failures is currently 24. We determined that the minimum wall thickness of the SAP cylinder assemblies, P/Ns SA52000-A1, SA52000-A20P, SA52000-A21P, SA52000-A22P, SA52000-A23P, SA55000-A1, SA55000-A20P, is significantly thinner in the failure location than the original equipment manufacturer (OEM) cylinders. We certified the SAP cylinders as equivalent replacement Parts Manufacturer Approval (PMA) parts for TCM 520 and 550 series engines, however, this design discrepancy results in stresses in the cylinder wall that are much higher in the SAP cylinder assemblies than in the OEM cylinder assemblies when subjected to identical loading. These higher stresses result in a lower fatigue life for the SAP cylinder assemblies relative to that of the OEM parts. The time-to-cracking or separation for this failure mode ranges between 823 hours time-since-new (TSN) and 1,985 TSN. The thin-wall thickness condition in the area of the exhaust valve seat of the cylinder head has been present since the initial SAP design, and it is present in all SAP cylinders of that design that have been manufactured to date. This condition, if not corrected, could result in immediate loss of engine power, possible structural damage to the engine, and possible fire in the engine compartment.

FAA's Determination and Requirements of the Proposed AD

We have evaluated all pertinent information and identified an unsafe condition that is likely to exist or develop on other products of this same type design. We are proposing this AD, which would require inspecting or replacing, or both, certain SAP cylinder assemblies within 25 flight hours TIS after the effective date of the proposed AD for cylinders that are at their respective time-before-overhaul (TBO) TIS flight hours or have exceeded their respective TBO TIS flight hours.

Costs of Compliance

We estimate that this proposed AD could affect 8,000 engines installed on airplanes of U.S. registry. We also estimate that it would take about 5 work-hours per cylinder to perform the proposed actions, and that the average labor rate is $80 per work-hour. Required parts would cost about $1,150 per cylinder. Based on these figures, we estimate the total cost of the proposed AD to U.S. operators to be $12,400,000.

Authority for This Rulemaking

Title 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.

We 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.

Regulatory Findings

We have determined that this proposed AD would not have federalism implications under Executive Order 13132. This proposed AD would 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.

For the reasons discussed above, I certify that the proposed AD:

1. Is not a “significant regulatory action” under Executive Order 12866;

2. Is not a “significant rule” under the DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979); and

3. Would not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act.

We prepared a regulatory evaluation of the estimated costs to comply with this proposed AD. You may get a copy of this summary at the address listed under ADDRESSES .

The Proposed Amendment

Under the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend 14 CFR part 39 as follows: