AD 97-01-05

The Federal Aviation Administration (FAA) has verified two reports of inflight HPT disk post separations on Williams International Model FJ44-1A turbofan engines. One of these inflight post separations was uncontained. The investigation revealed that in both cases, high pressure turbine (HPT) disk blade retention posts separated due to cracking caused by material creep/fatigue. This condition, if not corrected, could result in other engines experiencing HPT disk blade retention post separations and turbine blade liberations, and subsequent losses of engine power. In addition, this condition could, if not corrected, result in other engines experiencing high disk speed uncontained liberation of disk posts and turbine blades, which could cause aircraft damage. The FAA has reviewed and approved the technical contents of Williams-Rolls Alert Service Bulletin (ASB) No. FJ44-A72-30, dated November 6, 1996, that describes procedures for eddy current inspections (ECI) for possible cracks in HPT disk blade retention posts; and ASB No. FJ44- A72-31, dated November 4, 1996, that describes procedures for replacement of existing HPT disks with advanced design HPT disks. Since an unsafe condition has been identified that is likely to exist or develop on other engines of the same design, this AD is being issued to locate possible cracks in HPT disk blade retention posts, which could lead to the liberation of the turbine blades that they retain, and subsequent loss of engine power. In addition, this AD is being issued to prevent the separation of HPT disk posts that could lead to a high disk speed uncontained liberation of disk posts and turbine blades, which could result in aircraft damage. This AD requires initial and repetitive ECI for possible cracks in HPT disk blade retention posts. The inspection population is divided into two groups, with the higher risk group listed by engine serial number (S/N). This group of HPT disks is at a higher risk due to a lower stress rupture strength characteristic. In addition, this AD requires replacement of the existing HPT disks, Part Number (P/N) 48629, with advanced design HPT disks, P/N 55291, by July 1, 1997, as terminating action to the inspection requirements of this AD. The calendar end-dates for this AD were determined based upon each suspect disk group's time to crack initiation, subsequent crack propagation rate, and its failure probability. In addition, the total in- service cycles and hours of each of the suspect disks of both groups, and the ASB replacement parts availability were contributing factors for determining the end-dates. These actions are required to be accomplished in accordance with the ASBs described previously. Since a situation exists that requires the immediate adoption of this regulation, it is found that notice and opportunity for prior public comment hereon are impracticable, and that good cause exists for making this amendment effective inless than 30 days. Comments Invited Although this action is in the form of a final rule that involves requirements affecting flight safety and, thus, was not preceded by notice and an opportunity for public comment, comments are invited on this rule. Interested persons are invited to comment on this rule by submitting such written data, views, or arguments as they may desire. Communications should identify the Rules Docket number and be submitted in triplicate to the address specified under the caption "ADDRESSES." All communications received on or before the closing date for comments will be considered, and this rule may be amended in light of the comments received. Factual information that supports the commenter's ideas and suggestions is extremely helpful in evaluating the effectiveness of the AD action and determining whether additional rulemaking action would be needed. Comments are specifically invited on the overall regulatory, economic, environmental, and energy aspects of the rule that might suggest a need to modify the rule. All comments submitted will be available, both before and after the closing date for comments, in the Rules Docket for examination by interested persons. A report that summarizes each FAA-public contact concerned with the substance of this AD will be filed in the Rules Docket. Commenters wishing the FAA to acknowledge receipt of their comments submitted in response to this notice must submit a self-addressed, stamped postcard on which the following statement is made: "Comments to Docket Number 96-ANE-39." The postcard will be date stamped and returned to the commenter. 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 final rule does not have sufficient federalism implications to warrant the preparation of a Federalism Assessment. The FAA has determined that this regulation is an emergency regulation that must be issued immediately to correct an unsafe condition in aircraft, and is not a "significant regulatory action" under Executive Order 12866. It has been determined further that this action involves an emergency regulation under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979). If it is determined that this emergency regulation otherwise would be significant under DOT Regulatory Policies and Procedures, a final regulatory evaluation will be prepared and placed in the Rules Docket. A copy of it, if filed, may be obtained from the Rules Docket at the location provided under the caption "ADDRESSES." 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 part 39 of the Federal Aviation Regulations (14 CFR part 39) as follows: PART 39 - AIRWORTHINESS DIRECTIVES 1. The authority citation for part 39 continues to read as follows: Authority: 49 USC 106(g), 40113, 44701. 39.13 - [AMENDED] 2. Section 39.13 is amended by adding the following new airworthiness directive: