AD 99-27-15

This amendment adopts a new airworthiness directive (AD) that is applicable to certain General Electric Company GE90 series turbofan engines. This action requires visually inspecting Ps3 and P3B sense lines and full authority digital engine control (FADEC) Ps3 and P3B sensing ports and fittings, cleaning Ps3 and P3B fittings and sensing ports, purging the Ps3 and P3B systems of moisture, and, if necessary, blending of high metal, nicks, burrs, or scratches on Ps3 and P3B fitting threads. This amendment is prompted by seven reports of loss of thrust control due to corruption of the signals to the FADEC caused by water freezing in the Ps3 sensing system. The actions specified in this AD are intended to prevent loss of thrust control due to corruption of the Ps3 and P3B signals to the FADEC which if it occurs in a critical phase of flight, could result in loss of aircraft control.

Final rule; request for comments.

99-27-15 General Electric Company: Amendment 39-11496. Docket 99-NE-62-AD. Issues December 29, 1999.
Applicability: General Electric Company (GE) Models GE90-76B, -77B, -85B, -90B, and -92B turbofan engines, installed on but not limited to Boeing 777 series airplanes.

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 (f) 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 loss of thrust control due to corruption of the Ps3 and P3B signals to the full authority digital engine control (FADEC), which if it occurs in a critical phase of flight, could result in loss of aircraft control, accomplish the following:

Initial Inspection, Cleaning, Moisture Purging, and Blending

(a) Perform the following initial actions in accordance with the Accomplishment Instructions, Section (3) of GE Alert Service Bulletin (ASB) No. 73-A0060, dated December 23, 1999:

(1) Inspect, clean, moisture purge, and if necessary, blend any high metal, nicks, or burrs on fitting threads, on one engine installed on Boeing 777 series aircraft, within 10 cycles-in-service (CIS) after the effective date of this AD.

(2) Inspect, clean, moisture purge, and if necessary, blend any high metal, nicks, or burrs on fitting threads, on the other engineinstalled on the Boeing 777 series aircraft, within 20 CIS after the effective date of this AD.

Credit for Previous Inspections, Cleaning, and Moisture Purging

(b) Engines that have been inspected, cleaned, and moisture purged in accordance with GE90 All Reps Wire, JSB99-11-24-1, Revision 1, dated November 25, 1999, may count those inspections, cleaning, and moisture purging as accomplished and must be inspected, cleaned, moisture purged, and if necessary, have any high metal, nicks, or burrs on fitting threads blended, in accordance with the Accomplishment Instructions, Section (3) of GE ASB No. 73-A0060, dated December 23, 1999, and the following schedule:

(1) Engines that have accumulated 30 CIS or greater since previous inspection, cleaning, and moisture purging on the effective date of the AD must repeat the required procedures within 5 CIS after the effective date of this AD.

(2) Engines that have accumulated less than 30 CIS since previous inspection, cleaning, and moisture purging on the effective date of this AD must repeat the required procedures within 30 CIS since last inspection, or within 5 CIS after the effective date of this AD, whichever occurs later.

New and Replacement Engines

(c) For new and replacement engines, perform the initial inspection, cleaning, and moisture purging, and if necessary, blend any high metal, nicks, or burrs on fitting threads, prior to accumulating 30 CIS since entering service in accordance with the Accomplishment Instructions, Section (3) of GE ASB No. 73-A0060, dated December 23, 1999.

Repetitive Inspections

(d) Thereafter, inspect, clean, and moisture purge, and if necessary, blend any high metal, nicks, or burrs on fitting threads each engine within 30 CIS since last inspection, in accordance with the Accomplishment Instructions, Section (3) of GE ASB No. 73-A0060, dated December 23, 1999.

Idle Leak Check

(e) After accomplishing the required actions of this AD, and prior toentry into service, perform an idle leak check to confirm no Ps3 or P3B sense system faults in accordance with the Accomplishment Instructions, Section (3), paragraph (14), of GE ASB No. 73-A0060, dated December 23, 1999.

No Simultaneous Actions
(f) Do not perform the actions required by this AD concurrently on both engines installed on a Boeing 777 series aircraft

Alternative Methods of Compliance

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

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

Ferry Flights

(h) Special flight permits may beissued 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.

Incorporation by Reference

(i) The actions required by this AD shall be done in accordance with GE ASB No. 73-A0060, dated December 23, 1999. 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 Company via Lockheed Martin Technology Services, 10525 Chester Road, Suite C, Cincinnati, OH 45215; telephone 513-672-8400, fax 513-672-8422. Copies may be inspected at the FAA, New England Region, Office of the Regional 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.

(j) This amendment becomes effective on January 11, 2000.

The Federal Aviation Administration (FAA) has received seven reports of loss of thrust control (LOTC) on General Electric Company (GE) Model GE90 turbofan engines installed on Boeing 777 series aircraft. Five LOTC events occurred in-flight and two occurred on the ground. The five in-flight LOTC events were temporary in that the engine recovered and continued to operate normally for the remainder of the flight.

Investigation

The investigation revealed that water can accumulate in the Ps3 and P3B pressure sensing system, which can freeze in the full authority digital engine control (FADEC) sensing ports or pressure line. Frozen water can result in a restriction or a blocked signal to the FADEC. This blocked signal can cause a corruption of the FADEC signal and result in abnormal engine start characteristics on the ground or lack of engine response to commanded thrust levels in flight. Although there have been no LOTC events attributed to icing of the P3B sensing system in the field, inspections have identified moisture in this system, which could freeze and corrupt the P3B signal to the FADEC as well. This condition, if not corrected, could result in LOTC due to blockage of the FADEC sense lines, which if it occurs in a critical phase of flight, could result in loss of aircraft control.

Simultaneous LOTC Events

The FAA is especially concerned about the possibility of simultaneous LOTC events on both engines installed on the Boeing 777 series aircraft due to common mode threats, such as certain atmospheric conditions that may result in ice in the Ps3 or P3B pressure sensing system and causing corrupted signals to the FADEC in both engines.

Interim Action

Both Ps3 and P3B pressure systems incorporate weep holes that allows drainage of water in the lines that may accumulate from condensation or ingested water; however, the field events and the investigation have determined that these design features may not always be effective in eliminating water from these systems. GE is assessing design changes that will prevent water from freezing in these systems and causing corruption of the signals to the FADEC. The requirements of this AD may change based on the ongoing investigation of the root cause and field inspection results, and future rulemaking may be necessary.

Service Information

The FAA has reviewed and approved the technical contents of GE Alert Service Bulletin (ASB) GE90 73-A0060, dated December 23, 1999, that describes procedures for visually inspecting Ps3 and P3B sense lines and FADEC sensing ports and fittings, cleaning Ps3 and P3B fittings and sensor ports, purging the Ps3 and P3B systems of moisture, and, if necessary, blending of high metal, nicks, burrs, or scratches on Ps3 and P3B fitting threads.

Difference between ASB and AD

This AD contains provisions for initial actions, and the ASB assumes that all operators have completed the initial actions based onfield reports. If, however, operators have already accomplished the required initial actions, they need not repeat those actions, but may proceed directly to accomplishing the repetitive actions.

Required Actions

Since an unsafe condition has been identified that is likely to exist or develop on other engines of the same type design, this airworthiness directive (AD) is being issued to prevent engine LOTC events. This AD requires:

Visual inspections for high metal, nicks, burrs, or scratches on Ps3 and P3B fitting threads, and, if necessary, blending.
Visual inspections for moisture, debris, or ice in Ps3 and P3B FADEC fittings, ports, and open sense lines.
Cleaning of Ps3 and P3B FADEC fittings and sensing ports.
Purging of any moisture from the Ps3 and P3B sense system.
Engine idle leak check run following the maintenance activity to confirm no Ps3 or P3B sense system faults are present.

Compliance Times

One of the GE90 series engines installed on theBoeing 777 series airplane must have the initial inspection, cleaning, moisture purging, and, if necessary, blending of high metal, nicks, burrs, or scratches on Ps3 and P3B fitting threads, within 10 cycles-in-service (CIS) after the effective date of this AD. The other engine installed on the airplane must have the initial inspection, cleaning, moisture purging, and, if necessary, blending of high metal, nicks, burrs, or scratches, on Ps3 and P3B fitting threads, within 20 CIS after the effective date of this AD. Based on concerns over concurrent engine maintenance, engines installed on the same Boeing 777 series airplane must not have the inspection, cleaning, moisture purging and, if necessary, blending of high metal, nicks, burrs, or scratches on Ps3 and P3B fitting threads performed concurrently.

Credit for Previous Inspections, Cleaning, and Moisture Purging

Engines that have been inspected, cleaned, and moisture purged in accordance with GE90 All Reps Wire, JSB99-11-24-1, Revision 1, dated November 25, 1999, may count those inspections, cleaning, and moisture purging as accomplished and must be inspected, cleaned, moisture purged, and, if necessary, have high metal, nicks, burrs, or scratches on Ps3 and P3B fitting threads blended, within 30 CIS since those last actions. Engines that have accumulated 30 CIS or greater since previous inspection, cleaning, and moisture purging on the effective date of the AD must repeat the required procedures within 5 CIS after the effective date of this AD. Engines that have accumulated less than 30 CIS since previous inspection, cleaning, and moisture purging on the effective date of this AD must repeat the required procedures within 30 CIS since last inspection, or within 5 CIS after the effective date of this AD, whichever occurs later.

Repetitive Actions

Thereafter, operators must inspect, clean, moisture purge, and, if necessary, blend high metal, nicks, burrs, or scratches on Ps3 and P3B fitting threads at intervals not to exceed 30 CIS since last inspection.

Immediate Adoption

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 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 99-NE-62-AD." The postcard will be date stamped and returned to the commenter.

Regulatory Impact

Theregulations adopted herein will 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. Therefore, it is determined that this final rule does not have federalism implications under Executive Order (EO) 13132.

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 EO 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: