AD 97-12-05

This amendment adopts a new airworthiness directive (AD) that is applicable to General Electric Company (GE) GE90 series turbofan engines. This action supersedes Telegraphic AD T97-09-51 that currently requires visual checks of the engine Debris Monitoring System (DMS) sensor for bearing debris, and, if necessary, performing procedures for additional maintenance actions. In addition, that AD requires replacing Variable Speed Constant Frequency (VSCF) gearshaft flange ball bearings that may incorporate rivets that are manufactured of improper material with serviceable bearings. This action references a later revision of the applicable Service Bulletin (SB) that includes additional engine serial numbers; however, these changes do not affect the Applicability or compliance requirements of this AD. This amendment is prompted by the issuance of the new revision to the SB. The actions specified by this AD are intended to prevent a VSCF gearshaft flange ball bearing failure, which could result in an inflight engine shutdown.

Final rule; request for comments.

97-12-05 General Electric Company: Amendment 39-10047. Docket No. 97-ANE-23-AD. Supersedes Telegraphic AD T97-09-51.
Applicability: General Electric Company (GE) GE90 series turbofan engines with Accessory Gearboxes (AGBs) installed, Part Numbers (P/Ns) 1650M71G03 and 1650M71G04. These engines are installed on Boeing 777 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 (c) 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 Variable Speed Constant Frequency (VSCF) gearshaft flange ball bearing failure, which could result in an inflight engine shutdown, accomplish the following:
(a) Perform a visual check of the engine Debris Monitoring System sensor for debris in accordance with paragraph 2(c) of the Accomplishment Instructions of GE Service Bulletin (SB) No. 79-011, dated April 9, 1997, as follows:
(1) For aircraft that have two engines installed incorporating AGBs, P/N 1650M71G03 or 1650M71G04, accomplish the following:
(i) Perform an initial visual check on one of the engines installed on the aircraft within 24 clock hours after the effective date of this AD, and thereafter, visually check that engine every other day, at intervals not to exceed 48 clock hours since last visual check.
(ii) Perform an initial visual check on the engine not inspected in accordance with paragraph (a)(1)(i) of this AD installed on the same aircraft on the following day, not to exceed 24 clock hours after the visual check of the engine checked in paragraph (a)(1)(i) of this AD; thereafter, visually check this engine every other day at intervals not to exceed 48 clock hours since last visual check.
(iii) The visual checks for both engines must be staggered at one day intervals for each engine.
(2) For aircraft that have one of the two engines installed incorporating AGBs, P/N 1650M71G03 or 1650M71G04, perform the initial visual check on that engine within 24 clock hours after the effective date of this AD, and thereafter, visually check that engine every other day at intervals not to exceed 48 clock hours since last visual check.
(3) If the visual check indicates that debris is present, perform additional maintenance actions in accordance with paragraph 2(c) of the Accomplishment Instructionsof GE SB No. 79-011, dated April 9, 1997, prior to further flight.
(b) For engines that contain VSCF gearshaft flange ball bearings that may incorporate rivets manufactured from improper material, identified by serial numbers: 900-147, 900-149, 900-151, 900-106, and 900-153, within 7 days after the effective date of this AD, and for engines identified by serial numbers: 900-150, 900-156, 900-157, 900-158, prior to entry into revenue service, accomplish one of the following:
(1) Remove from service VSCF gearshaft flange ball bearings and replace with serviceable bearings in accordance with the Accomplishment Instructions of GE SB No. 72-280, Revision 3, dated April 15, 1997; or
(2) Remove and replace the 4,500 pound inches VSCF gearshaft assembly with the 3,500 pound inches gearshaft assembly installed in AGB, P/N 1650M71G02, in accordance with the Accomplishment Instructions of GE SB No. 72-283, Revision 4, dated April 17, 1997. Accomplishment of this option constitutes terminating action to the inspection requirements of paragraph (a) of this AD; or
(3) Remove and replace the 4,500 pound inches VSCF gearshaft assembly with the 4,500 pound inches gearshaft assembly containing select fit internal radial clearance flange ball bearings, in accordance with the Accomplishment Instructions of GE SB No. 72-286, dated April 14, 1997.
(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. 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.
(d) 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.
(e) The actions required by this AD shall be accomplished in accordance with the following GE SBs:

Document No.
Page
Revision
Date
72-283
1,2
4
April 17, 1997

3-10
Original
March 12, 1997

11,12
1
March 20, 1997

13
Original
March 12, 1997
Total Pages: 13.

72-280
1,2
3
April 15, 1997

3-12
2
March 19, 1997
Total Pages: 12.

72-286
1-15
Original
April 14, 1997
Total Pages: 15.

79-011
1-6
Original
April 9, 1997
Total Pages: 6.

This incorporation by reference was approved by the Director of the Federal Register in accordance with 5 U.S.C. 552(a) and 1 CFR part 51. Copies may be obtained from General Electric Technical Services, Attention: Leader For Distribution/Microfilm, 10525 Chester Road, Cincinnati, OH 45215; fax (513) 672-8422, telephone (513) 672-8400 Ext. 114. 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.
(f) This amendment supersedes Telegraphic AD T97-09-51, issued April 22, 1997.
(g) This amendment becomes effective on June 27, 1997.

On April 22, 1997, the Federal Aviation Administration (FAA) issued Telegraphic airworthiness directive (AD) T97-09-51, applicable to General Electric Company (GE) GE90 series turbofan engines, which requires visual checks of the engine Debris Monitoring System (DMS) sensor for bearing debris, and, if necessary, performing procedures for additional maintenance actions. In addition, that AD requires replacing Variable Speed Constant Frequency (VSCF) gearshaft flange ball bearings that may incorporate rivets that are manufactured of improper material with serviceable bearings. That action was prompted by reports of two recent failures of the Accessory Gearbox (AGB) VSCF gearshaft flange ball bearing, Part Number (P/N) 1770M41P01. This ball bearing is installed on the VSCF gearshaft which is located in the AGB and drives the Boeing 777 VSCF generator. The VSCF generator is a backup power supply for the Boeing 777 airplane. The ball bearing that failed is installed in GE90 AGBs, P/Ns 1650M71G03 and 1650M71G04. A third AGB configuration incorporates a different ball bearing design and has no reported service problems. The bearing failure investigation is ongoing; however, there is evidence that suggests the failures may be attributed to bearing operation with insufficient internal radial clearances that results in excessive ball to cage pocket forces causing bearing distress and premature failure. The investigation has also determined that a population of the VSCF gearshaft ball bearings, P/N 1770M41P01, may contain improper cage rivet material. Metallurgical evaluation of the rivets installed in the two failed VSCF gearshaft flange ball bearings has confirmed both bearings contained rivets manufactured from improper material. Results of the engineering analysis and testing suggest the improper rivet material may be a contributor to premature bearing distress when the improper rivets are installed in a bearing that contains insufficient internal radial clearance. That condition, if not corrected, could result in a VSCF gearshaft flange ball bearing failure, which could result in an inflight engine shutdown.
Since the issuance of that Telegraphic AD, GE has issued Revision 4, dated April 17, 1997, to Service Bulletin (SB) No. 72-283, which adds additional engine serial numbers; however, these changes do not affect the Applicability or compliance requirements of this AD. This AD references this revised SB.
The FAA has reviewed and approved the technical contents of GE SB No. 79-011, dated April 9, 1997, that describes procedures for monitoring the engine lubrication system for bearing debris, and, if necessary, the procedures for additional maintenance actions; GE SB No. 72-280, Revision 3, dated April 15, 1997, that describes procedures for replacement of certain VSCF gearshaft flange ball bearings that may incorporate improper rivet material; GE SB No. 72-283, Revision 4, dated April 17, 1997, that describes the procedures for replacing the 4,500 pound inches gearshaft assembly used in AGBs, P/Ns 1650M71G03 and 1650M71G04, with the 3,500 pound inches gearshaft assembly used in the AGB, P/N 1650M71G02; and GE SB No. 72-286, dated April 14, 1997, that describes procedures for replacing the VSCF gearshaft assembly with a VSCF gearshaft assembly containing a flange ball bearing with a select fit internal radial clearance.
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 Telegraphic AD T97-09-51 to require, within 24 hours after the effective date of this AD, a visual check of the engine DMS sensor for bearing debris, and, if necessary, performing procedures for additional maintenance actions. Thereafter, this AD requires visual checks of the engine DMS sensor for bearing debris at staggered one day intervals for each affected engine on the Boeing 777 (inspecting each engine every other day). Inaddition, this AD requires replacing VSCF gearshaft flange ball bearings that may incorporate rivets that are manufactured of improper material with serviceable bearings. Replacing the VSCF gearshaft assembly in accordance with GE SB No. 72-283, Revision 4, dated April 17, 1997, or GE SB No. 72-286, dated April 14, 1997, constitutes an acceptable alternative to the replacement of the affected bearing.
This AD defines interim requirements to prevent a VSCF gearshaft flange ball bearing failure. These requirements may be amended in further rulemaking as additional information from the failure investigation is obtained and corrective action is defined. The actions are required to be accomplished in accordance with the SBs 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-23." 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 havesufficient 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 adding the following new airworthiness directive: