AD 94-03-02

This amendment adopts a new airworthiness directive (AD) that is applicable to Pratt & Whitney Canada PW100 series turboprop engines. This action requires a life limit reduction for affected high pressure turbine (HPT) disks, and establishes a drawdown schedule for disks currently near, at, or greater than the new reduced service life. This amendment is prompted by reports of two HPT disk failures, one of which was uncontained. The actions specified in this AD are intended to prevent an uncontained HPT disk failure and damage to the aircraft.

Final rule, request for comments.

94-03-02 Pratt & Whitney Canada: Amendment 39-8808. Docket 94-ANE-04.
Applicability: Pratt & Whitney Canada (PWC) Model PW118, PW118A, PW120, PW120A, PW121, PW123, PW124B, and PW125B turboprop engines, installed on but not limited to de Havilland DHC-8 series, Embraer EMB-120 series, ATR-42 and -72 series, Fokker 50 series, Canadair Models CL-215T and 415, Dornier 328 series, British Aerospace ATP series, and XAC Y7-200A aircraft.
Compliance: Required as indicated, unless accomplished previously.
To prevent an uncontained HPT disk failure and damage to the aircraft, accomplish the following:
(a) Remove from service high pressure turbine (HPT) disks, part numbers (P/N) 3035711 and 3038411, and replace with a serviceable part in accordance with the following schedule, based on cycles in service (CIS) on the effective date of this airworthiness directive (AD):
(1) For disks with 13,000 or more CIS, remove within the next 1,000 CIS after the effective date of this AD,but not to exceed 15,000 total CIS.
(2) For disks with 12,000 or more CIS, but less than 13,000 CIS, remove within the next 1,250 CIS, but not to exceed 14,000 total CIS.
(3) For disks with 10,000 or more CIS, but less than 12,000 CIS, remove within the next 1,750 CIS, but not to exceed 13,250 total CIS.
(4) For disks with 8,000 or more CIS, but less than 10,000 CIS, remove within the next 2,500 CIS, but not to exceed 12,000 total CIS.
(5) For disks with less than 8,000 CIS, remove at or prior to accumulating 10,000 total CIS.
(b) This AD establishes a new service cycle life limit for HPT disks, P/N 3035711 and 3038411, of 10,000 total CIS. NOTE: Further information on the life limit reduction for affected HPT disks can be found in PWC Service Information Letter No. 307, dated December 17, 1993.
(c) An alternative method of compliance or adjustment of the compliance time that provides an acceptable level of safety may be used if approved by the Manager, Engine Certification Office. The request should be forwarded through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Engine Certification Office. NOTE: Information concerning the existence of approved alternative methods of compliance with this airworthiness directive, if any, may be obtained from the Engine Certification Office.
(d) Special flight permits may be issued in accordance with FAR 21.197 and 21.199 to operate the aircraft to a location where the requirements of this AD can be accomplished.
(e) This amendment becomes effective on February 16, 1994.

Transport Canada, which is the airworthiness authority for Canada, recently notified the Federal Aviation Administration (FAA) that an unsafe condition may exist on Pratt & Whitney Canada (PWC) Model PW118, PW118A, PW120, PW120A, PW121, PW123, PW124B, and PW125B turboprop engines. Transport Canada advises that they have received reports of two high pressure turbine (HPT) disk failures in the rim region with subsequent inflight engine shutdowns. Both disks failed at the same location in low cycle fatigue. One event was fully contained within the engine casings; the second event liberated some small debris through the engine nacelle.

Transport Canada issued AD CF-94-01, dated January 5, 1994, in order to assure the airworthiness of these PWC PW100 series turboprop engines in Canada.

This engine model is manufactured in Canada and is type certificated for operation in the United States under the provisions of Section 21.29 of the Federal AviationRegulations and the applicable bilateral airworthiness agreement. Pursuant to this bilateral airworthiness agreement, Transport Canada has kept the FAA informed of the situation described above. The FAA has examined the findings of Transport Canada, reviewed all available information, and determined that AD action is necessary for products of this type design that are certificated for operation in the United States.

Since an unsafe condition has been identified that is likely to exist or develop on other PWC PW100 series turboprop engines of the same type design registered in the United States, the proposed AD would require a life limit reduction for affected HPT disks, and establishes a drawdown schedule to manage disks currently near, at, or greater than the new reduced service life, without significant effect on flight safety or economic factors. The FAA has determined that a reduction in cyclic life limit, based on demonstrated crack initiation and propagation rates, wouldminimize the possibility of a disk failure, and restore the level of safety required at the time of type certification.

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 in less 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 94-ANE-04." The postcard will be date stamped and returnedto 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 14 CFR part 39 of the Federal Aviation Regulations as follows:

PART 39 - AIRWORTHINESS DIRECTIVES
1. The authority citation for part 39 continues to read as follows: Authority: 49 U.S.C. App. 1354(a), 1421 and 1423; 49 U.S.C. 106(g); and 14 CFR 11.89.

39.13 - [AMENDED]
2. Section 39.13 is amended by adding the following new airworthiness directive: