### 20508 Federal Register / Vol. 77, No. 66 / Thursday, April 5, 2012 / Rules and Regulations

AD: Within 60 months after the effective date of this AD, do the actions specified in paragraphs (g)(1) and (g)(2) of this AD.

(1) Replace the power control relays for the main tank fuel boost pumps with new relays having a ground fault interrupter (GFI) feature; do applicable electrical bonding resistance measurements between the GFI relays and their installation panel to verify that applicable bonding requirements are met; and do an operational test to ensure correct operation; as specified in Boeing Service Bulletin 757–28A0078, Revision 2, dated January 11, 2012 (for Model 757–200, –200CB, and –200PF series airplanes); or Boeing Service Bulletin 757–28A0079, Revision 2, dated January 11, 2012 (for Model 757–300 series airplanes). Do all actions in accordance with Part 1 of the Accomplishment Instructions of Boeing Service Bulletin 757–28A0078, Revision 2, dated January 11, 2012 (for Model 757–200, –200CB, and –200PF series airplanes); or Boeing Service Bulletin 757–28A0079, Revision 2, dated January 11, 2012 (for Model 757–300 series airplanes).

(2) Replace the power control relays for the center tank override fuel boost pumps with new relays having a GFI feature, in accordance with the actions required in paragraph (g)(2)(i) or (g)(2)(ii) of this AD.

(i) Replace the power control relays with new relays having a GFI feature; do applicable electrical bonding resistance measurements between the GFI relays and their installation panel to verify that applicable bonding requirements are met; and do an operational test to ensure correct operation; as specified in Boeing Service Bulletin 757–28A0078, Revision 2, dated January 11, 2012 (for Model 757–200, –200CB, and –200PF series airplanes); or Boeing Service Bulletin 757–28A0079, Revision 2, dated January 11, 2012 (for Model 757–300 series airplanes). Do all actions in accordance with Part 1 of the Accomplishment Instructions of Boeing Service Bulletin 757–28A0078, Revision 2, dated January 11, 2012 (for Model 757–200, –200CB, and –200PF series airplanes), or Boeing Service Bulletin 757–28A0079, Revision 2, dated January 11, 2012 (for Model 757–300 series airplanes).

(ii) Install and maintain TDG Aerospace universal fault interrupters (UFIs), in accordance with a method approved by the Manager, Seattle Aircraft Certification Office (ACO), FAA.

Note 1 to paragraph (g)(2)(ii) of this AD: Guidance on installing TDG Aerospace UFIs can be found in Supplemental Type Certificate ST01950LA ( http://rgl.faa.gov/ Regulatory

_ and

_ Guidance

_Library/rgSTC. nsf/0/196ec7e864607b5b862573c5007cb3b5/ $FILE/ST01950LA.pdf ).

(h) Inspection

For airplanes on which the actions specified in Boeing Alert Service Bulletin 757–28A0078, dated July 16, 2008, or 757– 28A0079, dated July 16, 2008, have been accomplished before the effective date of this AD: Within 60 months after the effective date of this AD, do a general visual inspection to verify that each GFI installation screw has enough grip length to hold the screws in each nut plate, and do applicable electrical bonding resistance measurements between the GFI relays and their installation panel to verify that applicable bonding requirements are met. If the screw does not have enough grip length, before further flight, install a longer screw. Do all actions in accordance with Part 2 of the Accomplishment Instructions of Boeing Service Bulletin 757– 28A0078, Revision 2, dated January 11, 2012 (for Model 757–200, –200CB, and –200PF series airplanes); or Boeing Service Bulletin 757–28A0079, Revision 2, dated January 11, 2012 (for Model 757–300 series airplanes).

(i) Credit for Previous Actions

This paragraph provides credit for the actions required by this AD, if those actions were performed before the effective date of this AD using Boeing Service Bulletin 757– 28A0078 or 757–28A0079, both Revision 1, both dated August 24, 2010.
(j) Alternative Methods of Compliance (AMOCs)

(1) The Manager, Seattle ACO, FAA, has the authority to approve AMOCs for this AD, if requested using the procedures found in 14 CFR 39.19. In accordance with 14 CFR 39.19, send your request to your principal inspector or local Flight Standards District Office, as appropriate. If sending information directly to the manager of the ACO, send it to the attention of the person identified in the Related Information section of this AD. Information may be emailed to: 9-ANMSeattle-ACO-AMOC-Requests@faa.gov.

(2) Before using any approved AMOC, notify your appropriate principal inspector, or lacking a principal inspector, the manager of the local flight standards district office/ certificate holding district office.

(k) Related Information

For more information about this AD, contact Georgios Roussos, Aerospace Engineer, Systems and Equipment Branch, ANM–130S, Seattle ACO, FAA, 1601 Lind Avenue SW., Renton, Washington 98057– 3356; phone: (425) 917–6482; fax: (425) 917– 6590; email: Georgios.Roussos@faa.gov. Or, email information to 9-ANM-Seattle-ACOAMOC-Requests@faa.gov.
(l) Material Incorporated by Reference

(1) You must use the following service information to do the actions required by this AD, unless the AD specifies otherwise. The Director of the Federal Register approved the incorporation by reference (IBR) under 5 U.S.C. 552(a) and 1 CFR part 51 of the following service information:

(i) Boeing Service Bulletin 757–28A0078, Revision 2, dated January 11, 2012.

(ii) Boeing Service Bulletin 757–28A0079, Revision 2, dated January 11, 2012.

(2) For service information identified in this AD, contact Boeing Commercial Airplanes, Attention: Data & Services Management, P.O. Box 3707, MC 2H–65, Seattle, Washington 98124–2207; telephone 206–544–5000, extension 1; fax 206–766– 5680; email me.boecom@boeing.com; Internet https://www.myboeingfleet.com.

(3) You may review copies of the service information at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington. For information on the availability of this material at the FAA, call
425–227–1221.

(4) You may also review copies of the service information that is incorporated by reference at the National Archives and Records Administration (NARA). For information on the availability of this material at an NARA facility, call 202–741– 6030, or go to http://www.archives.gov/ federal

_ register/code

_ of

_ federal

_regulations/ ibr

_ locations.html. Issued in Renton, Washington, on March 9,
2012. Ali Bahrami, Manager, Transport Airplane Directorate, Aircraft Certification Service.

[FR Doc. 2012–6642 Filed 4–4–12; 8:45 am]

**BILLING CODE 4910–13–P**

**DEPARTMENT OF TRANSPORTATION**

**Federal Aviation Administration**

**14 CFR Part 39**

**[Docket No. FAA–2010–0821; Directorate Identifier 2010–NE–30–AD; Amendment 39–**  **17004; AD 2012–06–23]**

**RIN 2120–AA64**

**Airworthiness Directives; Rolls-Royce plc Turbofan Engines** 

**AGENCY :**  Federal Aviation Administration (FAA), DOT.

**ACTION :**  Final rule; request for
comments.

**SUMMARY :**  We are superseding an existing airworthiness directive (AD) for all Rolls-Royce plc (RR) RB211–Trent 875–17, RB211–Trent 877–17, RB211– Trent 884–17, RB211–Trent 884B–17, RB211–Trent 892–17, RB211–Trent 892B–17, and RB211–Trent 895–17 turbofan engines. That AD currently requires initial and repetitive ultrasonic inspections (UIs) of certain low-pressure (LP) compressor blades identified by serial number (S/N). This AD requires the same actions but expands the population of blades. This AD was prompted by RR concluding that additional blades affected must be inspected. We are issuing this AD to prevent LP compressor blades from failing due to blade root cracks, which could lead to uncontained engine failure and damage to the airplane.

**DATES :**  This AD is effective April 20,
2012.

The Director of the Federal Register approved the incorporation by reference of a certain publication listed in the AD as of April 20, 2012.

We must receive any comments on this AD by May 21, 2012.

**ADDRESSES :**  You may send comments by any of the following methods:


### 20509 Federal Register / Vol. 77, No. 66 / Thursday, April 5, 2012 / Rules and Regulations

• Federal eRulemaking Portal: Go to http://www.regulations.gov. Follow the instructions for submitting comments.

• Fax: 202–493–2251.

• Mail: U.S. Department of Transportation, Docket Operations, M–30, West Building Ground Floor, Room W12–140, 1200 New Jersey Avenue SE., Washington, DC 20590.

• Hand Delivery: U.S. Department of Transportation, Docket Operations, M–30, West Building Ground Floor, Room W12–140, 1200 New Jersey Avenue SE., Washington, DC 20590, between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays.

For service information identified in this AD, contact Rolls-Royce plc, Corporate Communications, P.O. Box 31, Derby, England, DE248BJ, telephone: 011–44–1332–242424; fax: 011–44– 1332–245418, or email: http://www.rollsroyce.com/contact/civil

_ team.jsp. You may review copies of the referenced service information at the FAA, Engine & Propeller Directorate, 12 New England Executive Park, Burlington, MA. For information on the availability of this material at the FAA, call 781–238–7125. Examining the AD Docket

You may examine the AD docket on the Internet at http:// www.regulations.gov; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this AD, the regulatory evaluation, any comments received, and other information. The street address for the Docket Office (phone: 800–647– 5527) is in the **ADDRESSES** section. Comments will be available in the AD docket shortly after receipt.

**FOR FURTHER INFORMATION CONTACT :**  Alan Strom, Aerospace Engineer, Engine Certification Office, FAA, Engine & Propeller Directorate, 12 New England Executive Park, Burlington, MA 01803; phone: 781–238–7143; fax: 781–238– 7199; email: alan.strom@faa.gov.

**SUPPLEMENTARY INFORMATION :** 

Discussion

On April 1, 2011, we issued AD 2011– 08–07, Amendment 39–16657 (76 FR 24798, May 3, 2011), for all RR RB211– Trent 875–17, RB211–Trent 877–17, RB211–Trent 884–17, RB211–Trent 884B–17, RB211–Trent 892–17, RB211– Trent 892B–17, and RB211–Trent 895– 17 turbofan engines. On September 9, 2011, we also issued a correction (76 FR 59013, September 23, 2011) to that AD. That AD requires initial and repetitive UIs of certain LP compressor blades identified by S/N. That AD resulted from mandatory continuing airworthiness information (MCAI) issued by an aviation authority of another country to identify and correct an unsafe condition on an aviation product. We issued that AD to prevent LP compressor blades from failing due to blade root cracks, which could lead to uncontained engine failure and damage to the airplane.

Actions Since AD Was Issued

Since we issued AD 2011–08–07 (76 FR 24798, May 3, 2011), RR determined that additional S/Ns of LP compressor blades are affected and require inspection. EASA has also issued AD 2012–0025, dated February 8, 2012, to expand the population of affected LP compressor blades operating in Europe. About 2,300 of the added blades require inspection within 70 cycles of the effective date of the AD since those blades have more fatigue damage from prior use.

This superseding AD differs from EASA AD 2012–0025. This AD only requires inspection of LP compressor blades that are listed in Appendices 3A through 3G of RR Alert Service Bulletin (ASB) No. RB.211–72–AG244, Revision 4, dated December 22, 2011. We are developing another AD to require inspection of LP compressor blades listed in Appendices 3H through 3L of RR ASB No. RB.211–72–AG244, Revision 4, dated December 22, 2011.

Relevant Service Information

We reviewed Rolls-Royce plc ASB No. RB.211–72–AG244, Revision 4, dated December 22, 2011. The service information describes procedures for performing UIs of the LP compressor blades.

FAA’s Determination

We are issuing this AD because we evaluated all the relevant information and determined the unsafe condition described previously is likely to exist or develop in other products of the same type design.
AD Requirements

This AD requires accomplishing the actions specified in the service information described previously except that this AD only requires inspection of LP compressor blades that are listed in Appendices 3A through 3G of RR ASB No. RB.211–72–AG244, Revision 4, dated December 22, 2011.
FAA’s Justification and Determination of the Effective Date

An unsafe condition exists that requires the immediate adoption of this AD. The FAA has found that the risk to the flying public justifies waiving notice and comment prior to adoption of this rule because about 2,300 LP compressor blades require inspection within 70 cycles after the effective date of the AD. This equates to about one month’s time for Trent 800 engines flying two flights per day. Therefore, we find that notice and opportunity for prior public comment are impracticable and that good cause exists for making this amendment effective in less than 30 days.

Comments Invited

This AD is a final rule that involves requirements affecting flight safety, and we did not provide you with notice and an opportunity to provide your comments before it becomes effective. However, we invite you to send any written data, views, or arguments about this AD. Send your comments to an address listed under the **ADDRESSES** section. Include the docket number FAA–2010–0821 and directorate identifier 2010–NE–30–AD at the beginning of your comments. We specifically invite comments on the overall regulatory, economic, environmental, and energy aspects of this AD. We will consider all comments received by the closing date and may amend this AD because of those
comments.

We will post all comments we receive, without change, to http:// www.regulations.gov, including any personal information you provide. We will also post a report summarizing each substantive verbal contact we receive about this AD. Costs of Compliance

Based on the service information, we estimate that this AD will affect about 158 engines installed on airplanes of U.S. registry. We also estimate that it will take about 3 hours per engine inspection, and six inspections per year.The average labor rate is $85 per workhour. We estimate that one LP compressor blade per year will need replacement, at a cost of about $82,000. Based on these figures, we estimate the annual cost of the AD on U.S. operators to be $323,740. Our cost estimate is exclusive of possible warranty coverage. Authority for This Rulemaking

Title 49 of the United States Code specifies the FAA’s authority to issue rules on aviation safety. Subtitle I, Section 106, describes the authority of the FAA Administrator. Subtitle VII, Aviation Programs, describes in more detail the scope of the Agency’s authority.

We are issuing this rulemaking under the authority described in Subtitle VII,


### 20510 Federal Register / Vol. 77, No. 66 / Thursday, April 5, 2012 / Rules and Regulations

Part A, Subpart III, Section 44701, ‘‘General requirements.’’ Under that section, Congress charges the FAA with promoting safe flight of civil aircraft in air commerce by prescribing regulations for practices, methods, and procedures the Administrator finds necessary for safety in air commerce. This regulation is within the scope of that authority because it addresses an unsafe condition that is likely to exist or develop on products identified in this rulemaking action. Regulatory Findings

This AD will not have federalism implications under Executive Order 13132. This AD 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.

For the reasons discussed above, I certify that this AD:

(1) Is not a ‘‘significant regulatory action’’ under Executive Order 12866,

(2) Is not a ‘‘significant rule’’ under DOT Regulatory Policies and Procedures (44 FR 11034, February 26, 1979),

(3) Will not affect intrastate aviation in Alaska, and (4) Will not have a significant economic impact, positive or negative, on a substantial number of small entities under the criteria of the Regulatory Flexibility Act. List of Subjects in 14 CFR Part 39

Air transportation, Aircraft, Aviation safety, Incorporation by reference, Safety. Adoption of the Amendment

Accordingly, under the authority delegated to me by the Administrator, the FAA 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. The FAA amends § 39.13 by removing airworthiness directive (AD) 2011–08–07, Amendment 39–16657 (76 FR 24798, May 3, 2011) and adding the following new AD:
2012–06–23 Rolls-Royce plc: Amendment 39–17004; Docket No. FAA–2010–0821; Directorate Identifier 2010–NE–30–AD. (a) Effective Date This airworthiness directive (AD) becomes effective April 20, 2012.

(b) Affected ADs

This AD supersedes AD 2011–08–07, Amendment 39–16657 (76 FR 24798, May 3, 2011).
(c) Applicability

This AD applies to Rolls-Royce plc (RR) RB211–Trent 875–17, RB211–Trent 877–17, RB211–Trent 884–17, RB211–Trent 884B–17, RB211–Trent 892–17, RB211–Trent 892B–17, and RB211–Trent 895–17 turbofan engines.

(d) Unsafe Condition

This AD was prompted by the determination by RR that additional serial numbers (S/Ns) of low-pressure (LP) compressor blades are affected and need to be inspected. We are issuing this AD to prevent LP compressor blades from failing due to blade root cracks, which could lead to uncontained engine failure and damage to the airplane.
(e) Actions and Compliance

Unless already done, do the following actions.

(1) Perform an initial ultrasonic inspection (UI) of the affected LP compressor blades identified by S/N in Appendices 3A through 3G of RR Alert Service Bulletin (ASB) No. RB.211–72–AG244, Revision 4, dated December 22, 2011. Use Table 1 of this AD to determine your initial inspection threshold.



### T ABLE 

### 1—I NITIAL 

### I NSPECTION 

### T HRESHOLDS

Appendix number of RR ASB No. RB.211–72–AG244, revision 4, that identifies affected LP compressor blades by S/N Initial inspection threshold

3A and 3B ................................................................................................. Within 70 flight cycles after the effective date of this AD. 3C ............................................................................................................. Within 10 months after the effective date of this AD. 3D ............................................................................................................. Within 22 months after the effective date of this AD. 3E ............................................................................................................. Within 34 months after the effective date of this AD. 3F .............................................................................................................. Within 46 months after the effective date of this AD. 3G ............................................................................................................. Within 58 months after the effective date of this AD.

(2) Thereafter, perform repetitive UIs of the affected LP compressor blades within every 100 flight cycles.

(3) Use paragraphs 3.A.(1) through 3.A.(2) of Accomplishment Instructions of RR ASB No. RB.211–72–AG244, Revision 4, dated December 22, 2011, and paragraphs 1 through 3.B. of Appendix 1 of that ASB, or paragraphs 3.B.(1) through 3.B.(3) of Accomplishment Instructions of RR ASB No. RB.211–72–AG244, Revision 4, dated December 22, 2011, and paragraphs 1 through 3.C. of Appendix 2 of that ASB, to perform the UIs.

(4) Do not return to service any engine with blades that failed the inspection required by this AD.

(5) For blades that are removed from the engine and pass inspection, re-apply dry film lubricant, and install all blades in their original position.

(6) After the effective date of this AD, do not install any affected LP compressor blade unless it has passed the initial and repetitive UIs required by this AD.

(f) Credit for Previous Actions

You may take credit for the initial inspection that is required by paragraph (e)(1) of this AD if you performed the initial inspection before the effective date of this AD using RR ASB No. RB.211–72–AG244, dated August 7, 2009; ASB No. RB.211–72–AG244, Revision 1, dated January 26, 2010; ASB No. RB.211–72–AG244, Revision 2, dated August 18, 2011; or ASB No. RB.211–72–AG244, Revision 3, dated December 13, 2011.
(g) FAA AD Differences

This AD differs from EASA AD 2012–0025, dated February 8, 2012. That AD requires inspecting LP compressor blades that are listed in Appendices 3A through 3L of RR ASB No. RB.211–72–AG244, Revision 4, dated December 22, 2011, whereas this AD only requires inspection of LP compressor blades that are listed in Appendices 3A through 3G of the ASB.
(h) Alternative Methods of Compliance

The Manager, Engine Certification Office, FAA, may approve AMOCs for this AD. Use the procedures found in 14 CFR 39.19 to make your request.

(i) Related Information

(1) For more information about this AD, contact Alan Strom, Aerospace Engineer, Engine Certification Office, FAA, Engine & Propeller Directorate, 12 New England Executive Park, Burlington, MA 01803; phone: 781–238–7143; fax: 781–238–7199; email: alan.strom@faa.gov.

(2) Refer to EASA AD 2012–0025, dated February 8, 2012, for related information.
(j) Material Incorporated by Reference

(1) You must use Rolls-Royce plc Alert Service Bulletin No. RB.211–72–AG244, Revision 4, dated December 22, 2011,


### 20511 Federal Register / Vol. 77, No. 66 / Thursday, April 5, 2012 / Rules and Regulations

Appendix 1, Appendix 2, and Appendices 3A through 3G of that ASB, to do the actions required by this AD, unless the AD specifies otherwise. The Director of the Federal Register approved the incorporation by reference under 5 U.S.C. 552(a) and 1 CFR part 51.

(2) For service information identified in this AD, contact Rolls-Royce plc, Corporate Communications, P.O. Box 31, Derby, England, DE248BJ, telephone: 011–44–1332– 242424; fax: 011–44–1332–245418, or email: http://www.rolls-royce.com/contact/ civil

_ team.jsp. (3) You may review copies of the service information at the FAA, Engine & Propeller Directorate, 12 New England Executive Park, Burlington, MA. For information on the availability of this material at the FAA, call
781–238–7125.

(4) You may also review copies of the service information that is incorporated by reference at the National Archives and Records Administration (NARA). For information on the availability of this material at NARA, call 202–741–6030, or go
to: http://www.archives.gov/federal-register/ cfr/ibr

_locations.html. Issued in Burlington, Massachusetts, on March 20, 2012. Peter A. White, Manager, Engine & Propeller Directorate, Aircraft Certification Service.
[FR Doc. 2012–8163 Filed 4–4–12; 8:45 am]

**BILLING CODE 4910–13–P**

**DEPARTMENT OF TRANSPORTATION**

**Federal Aviation Administration**

**14 CFR Part 39**

**[Docket No. FAA–2010–0858; Directorate Identifier 2010–NM–183–AD; Amendment**  **39–16974; AD 2012–05–02]**

**RIN 2120–AA64**

**Airworthiness Directives; The Boeing Company Airplanes** 

**AGENCY :**  Federal Aviation Administration (FAA), DOT.

**ACTION :**  Final rule.

**SUMMARY :**  We are adopting a new airworthiness directive (AD) for certain The Boeing Company Model 737–600, –700, –700C, –800, and –900 series airplanes. This AD was prompted by reports of heat damage to the inner wall of the thrust reversers, which could result in separation of adjacent components and consequent structural damage to the airplane, damage to other airplanes, and injury to people on the ground. This AD requires modifying the thrust reverser inner walls, inspecting for damage of the upper and lower inner wall insulation blankets, measuring the electrical conductivity on the aluminum upper compression pads 2 and 3 as applicable, inspecting for discrepancies of the inner wall of the thrust reverser, and corrective actions if necessary. This AD also requires, for certain airplanes, doing various concurrent actions (including replacing the inner wall blanket insulation, installing updated full-authority digital electronic control software, and modifying the thrust reverser inner wall and insulation blankets). We are issuing this AD to correct the unsafe condition on these products.

**DATES :**  This AD is effective May 10,
2012.

The Director of the Federal Register approved the incorporation by reference of certain publications listed in the AD as of May 10, 2012.

**ADDRESSES :**  For Boeing service information identified in this AD, contact Boeing Commercial Airplanes, Attention: Data & Services Management, P.O. Box 3707, MC 2H–65, Seattle, Washington 98124–2207; telephone 206–544–5000, extension 1; fax 206– 766–5680; email me.boecom@boeing.com; Internet https://www.myboeingfleet.com. For CFM service information identified in this AD, contact CFM International, Technical Publications Department, 1 Neumann Way, Cincinnati, Ohio 45215; phone: 513–552–2800; fax: 513–552– 2816; Internet: http://www.cfm56.com. You may review copies of the referenced service information at the FAA, Transport Airplane Directorate, 1601 Lind Avenue SW., Renton, Washington. For information on the availability of this material at the FAA, call 425–227–1221. Examining the AD Docket

You may examine the AD docket on the Internet at http:// www.regulations.gov; or in person at the Docket Management Facility between 9 a.m. and 5 p.m., Monday through Friday, except Federal holidays. The AD docket contains this AD, the regulatory evaluation, any comments received, and other information. The address for the Docket Office (phone: 800–647–5527) is Document Management Facility, U.S. Department of Transportation, Docket Operations, M–30, West Building Ground Floor, Room W12–140, 1200 New Jersey Avenue SE., Washington, DC 20590.

**FOR FURTHER INFORMATION CONTACT :**  Chris Parker, Aerospace Engineer, Propulsion Branch, ANM–140S, FAA, Seattle Aircraft Certification Office (ACO), 1601 Lind Avenue SW., Renton, Washington 98057–3356; phone: 425– 917–6496; fax: 425–917–6590; email: chris.r.parker@faa.gov. **SUPPLEMENTARY INFORMATION :** 

Discussion

We issued a notice of proposed rulemaking (NPRM) to amend 14 CFR part 39 to include an airworthiness directive (AD) that would apply to The Boeing Company Model 737–600, –700, –700C, –800, –900, and –900ER series airplanes. That NPRM was published in the Federal Register on September 27, 2010 (75 FR 59167). That NPRM proposed to require modifying the inner walls of the thrust reverser (TR), inspecting for damage of the upper and lower inner wall insulation blankets, measuring the electrical conductivity on the aluminum upper compression pads 2 and 3 as applicable, inspecting for discrepancies of the TR inner wall, and corrective actions if necessary. That NPRM also proposed to require, for certain airplanes, doing various concurrent actions (including replacing the inner wall blanket insulation, installing updated full-authority digital electronic control software, and modifying the TR inner wall and insulation blankets).

Comments

We gave the public the opportunity to participate in developing this AD. The following presents the comments received on the proposal (75 FR 59167, September 27, 2010) and the FAA’s response to each comment. Request To Withdraw NPRM (75 FR 59167, September 27, 2010)

Despite fully supporting the implementation of the actions of the NPRM (75 FR 59167, September 27, 2010), Boeing stated that it does not consider thermal overheat on the TR inner walls on the affected airplanes to be a safety issue. The structural integrity of the inner wall may deteriorate due to pre-cooler air ingress behind the blankets, but the Boeing Safety Review Board determined that this does not constitute a safety hazard to the airplane or to persons on the ground. Boeing identified support data for this determination, which included a safety assessment, full-scale test demonstration, and structural analysis.

We infer that Boeing wants us to withdraw the NPRM (75 FR 59167, September 27, 2010), because there is no unsafe condition. We disagree. The thermal overheat could affect the structural capability of the inner wall of the thrust reverser such that, if a pneumatic duct bursts, the inner wall could fail, causing uncontrollable asymmetric thrust during a rejected takeoff, or causing large parts to hit the fuselage or empennage in flight.