AD 97-25-07

This amendment supersedes an existing airworthiness directive (AD), applicable to GE Aircraft Engines (GE) CT7 series turboprop engines, that currently requires eddy current inspection (ECI) of disk holes of stage 1 and 2 gas generator turbine (GGT) disks for cracks, and, if necessary, replacement with serviceable parts. This amendment increases the initial cyclic compliance threshold while decreasing the calendar time for performing the ECI. This amendment is prompted by corrections to the applicable alert service bulletin (ASB) serial number (S/N) tables. The ASB contained S/Ns which appeared in more than one table creating confusion over which cyclic limit applied to each S/N. The actions specified by this AD are intended to prevent a stage 1 or 2 GGT disk failure, which could result in an uncontained engine failure and damage to the aircraft.

Final rule; request for comments.

97-25-07 GE Aircraft Engines: Amendment 39-10231. Docket 97-ANE-41-AD. Supersedes AD 97-05-12, Amendment 39-9956.

Applicability: GE Aircraft Engines (GE) Models CT7-5A2, -7A, -9B, -9C turboprop engines, installed on but not limited to Construcciones Aeronauticas, SA (CASA) CN-235 series and SAAB-SCANIA SF340 series aircraft.

Note 1: This airworthiness directive (AD) applies to each engine identified in the preceding applicability provision, regardless of whether it has been modified, altered, or repaired in the area subject to the requirements of this AD. For engines that have been modified, altered, or repaired so that the performance of the requirements of this AD is affected, the owner/operator must request approval for an alternative method of compliance in accordance with paragraph (l) of this AD. The request should include an assessment of the effect of the modification, alteration, or repair on the unsafe condition addressed by this AD; and, if the unsafe condition has not been eliminated, the request should include specific proposed actions to address it.

Compliance: Required as indicated, unless accomplished previously.

To prevent a stage 1 or 2 gas generator turbine (GGT) disk failure, which could result in an uncontained engine failure and damage to the aircraft, accomplish the following:

(a) For all stage 1 GGT disks, Part Number (P/N) 6064T06P01, identified in Table 1 of GE (CT7-TP Series) Alert Service Bulletin (ASB) A72-393, Revision 1, dated February 13, 1997, that have accumulated 8,500 or more cycles since new (CSN) on the effective date of this AD, perform a one time eddy current inspection (ECI) for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) Service Bulletin (SB) 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, or not to exceed 3 months after the effective date of this AD, whichever occurs first.

(b) For all stage 1 GGT disks, P/N 6064T06P01, identified in Table 1 of GE (CT7-TP Series) ASB A72-393, Revision 1, dated February 13, 1997, that have accumulated less than 8,500 CSN on the effective date of this AD, perform a one time ECI for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) SB 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, but not to exceed 9,000 CSN.

(c) For all stage 1 GGT disks, P/N 6064T06P01, identified in Table 2 of GE (CT7-TP Series) ASB A72-393, Revision 1, dated February 13, 1997, that have accumulated 11,500 or more CSN on the effective date of this AD, perform a one time ECI for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) SB 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, or not to exceed 3 months after the effective date of this AD, whichever occurs first.

(d) For all stage 1 GGT disks, P/N 6064T06P01, identified in Table 2 of GE (CT7-TP Series) ASB A72-393, Revision 1,dated February 13, 1997, that have accumulated less than 11,500 CSN on the effective date of this AD, perform a one time ECI for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) SB 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, but not to exceed 12,000 CSN.

(e) For all stage 2 GGT disks, P/N 6064T12P01, identified in Table 3 of GE (CT7-TP Series) ASB A72-393, Revision 1, dated February 13, 1997, that have accumulated 8,500 or more CSN on the effective date of this AD, perform a one time ECI for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) SB 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, or not to exceed 3 months after the effective date of this AD, whichever occurs first.

(f) For all stage 2 GGT disks, P/N 6064T12P01, identified in Table 3 of GE (CT7-TP Series) ASB A72-393, Revision 1, dated February 13, 1997, that have accumulated less than 8,500 CSN on the effective date of this AD, perform a one time ECI for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) SB 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, but not to exceed 9,000 CSN.

(g) For all stage 2 GGT disks, P/N 6064T12P01, identified in Table 4 of GE (CT7-TP Series) ASB A72-393, Revision 1, dated February 13, 1997, that have accumulated 11,500 or more CSN on the effective date of this AD, perform a one time ECI for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) SB 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, or not to exceed 3 months after the effective date of this AD, whichever occurs first.

(h) For all stage 2 GGT disks, P/N 6064T12P01, identified in Table 4 of GE (CT7-TP Series) ASB A72-393, Revision 1, dated February 13, 1997, that have accumulated less than 11,500 CSN on the effective date of this AD, perform a one time ECI for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) SB 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, but not to exceed 12,000 CSN.

(i) For all stage 1 GGT disks, P/N 6064T06P01, and all stage 2 GGT disks, P/N 6064T12P01, not identified in Tables 1 through 4 of GE (CT7-TP Series) ASB A72-393, Revision 1, dated February 13, 1997, that have accumulated 8,500 or more CSN on the effective date of this AD, perform a one time ECI for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) SB 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, or not to exceed 3 months after the effective date of this AD, whichever occurs first.

(j) For all stage 1 GGT disks, P/N 6064T06P01, and all stage 2 GGT disks, P/N 6064T12P01, not identified in Tables 1 through 4 of GE (CT7-TP Series) ASB A72-393, Revision 1, dated February 13, 1997, that have accumulated less than 8,500 CSN on the effective date of this AD, perform a one time ECI for cracks in accordance with the Accomplishment Instructions of GE (CT7-TP Series) SB 72-390, Revision 1, dated December 11, 1996, at the next GGT module removal, but not to exceed 9,000 CSN.

(k) Prior to further flight, remove from service cracked disks, and replace with serviceable parts.

(l) 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. Operators shall submit their requests through an appropriate FAA Principal Maintenance Inspector, who may add comments and then send it to the Manager, Engine Certification Office.

Note 2: Information concerning the existence of approved alternative methods of compliance with this airworthiness directive, if any, may be obtained from the Engine Certification Office.

(m) Special flight permits may be issued in accordance with sections 21.197 and 21.199 of the Federal Aviation Regulations (14 CFR 21.197 and 21.199) to operate the aircraft to a location where the requirements of this AD can be accomplished.

(n) The actions required by this AD shall be done in accordance with the following GE (CT7-TP Series) service documents:

Document No.
Pages
Revision
Date
ASB A72-393
1-16
1
February 13, 1997
Total pages: 16.

SB 72-390
1-6
1
December 11, 1996
Total pages: 6.

(o) The incorporation by reference of GE (CT7-TP Series) SB 72-390, dated December 11, 1996, was previously approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51 as of April 14, 1997 (62 FR 15094).

(p) The incorporation by reference of GE (CT7-TP Series ) ASB A72-393, dated February 13, 1997, is approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51 as of January 28, 1998.

(q) Copies of the service documents may be obtained from GE Aircraft Engines, 1000 Western Ave., Lynn, MA 01910; telephone (781) 594-3140, fax (781) 594-4805. Copies may be inspected at the FAA, New England Region, Office of the Assistant Chief Counsel, 12 New England Executive Park, Burlington, MA; or at the Office of the Federal Register, 800 North Capitol Street, NW., suite 700, Washington, DC.

(r) This amendment becomes effective on January 28, 1998.

On February 24, 1997, the Federal Aviation Administration (FAA) issued airworthiness directive (AD) 97-05-12, Amendment 39-9956 (62 FR 15094, March 31, 1997), applicable to General Electric Aircraft Engines (GE) CT7 series turboprop engines, to require a one-time eddy current inspection (ECI) for cracks of disk holes of stage 1 and 2 gas generator turbine (GGT) disks, and, if necessary, replacement with serviceable parts. That action was prompted by a report of a GE CT7 series turboprop engine, installed on a SAAB-SCANIA SF340 aircraft, that experienced an uncontained stage 2 GGT failure during takeoff. The investigation revealed that the failure was caused by a crack in a disk cooling hole. The most likely cause of the cracking was machining damage to the disk cooling hole during manufacturing. That condition, if not corrected, could result in a stage 1 or 2 GGT disk failure, which could result in an uncontained engine failure and damage to the aircraft.

This amendment is prompted by a revision to the applicable alert service bulletin (ASB) that provides corrections to the serial number (S/N) tables. The ASB contained S/Ns which appeared in more than one table creating confusion over which cyclic limit applied to each S/N. This amendment supersedes the existing AD and increases the initial cyclic compliance threshold while decreasing the calendar time for performing the ECI. The compliance times have been adjusted to ensure that no part exceeds the cyclic limits nor the compliance end date as calculated by GE's risk analysis.

The FAA has reviewed and approved the technical contents of GE (CT7-TP Series) ASB A72-393, Revision 1, dated February 13, 1997, that lists by S/N affected stage 1 and 2 GGT disks, and GE (CT7-TP Series) Service Bulletin 72-390, Revision 1, dated December 11, 1996, that describes procedures for ECI of disk holes for cracks.

Since an unsafe condition has been identified that is likely to exist or develop on other engines of this same type design, this AD supersedes AD 97-05-12 to increase the initial cyclic compliance threshold while decreasing the calendar time for performing the ECI. The actions are required to be accomplished in accordance with the service documents 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 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 97-ANE-41-AD." 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 U.S.C. 106(g), 40113, 44701. 39.13 [Amended]

2. Section 39.13 is amended by removing Amendment 39-9956, (62 FR 15094, March 31, 1997), andby adding a new airworthiness directive, Amendment 39-10231, to read as follows: