U
, S, Deportment of T r ans p o rtat io n Federal Aviation Administration



### MA Y 1 2 2011

Air lndia Engine and Propeller Directorate

ATTN: Jagadeesan U mam ahe swa ran Engine Over haul Department Air India Santacru z East Mumbai, Maharashtra India
, 400029

Dear Mr. U mamaheswaran: Eng ine Certification Office 12 New England E xecutive Park Bur l inglon
, MA 0 18 03 (781) 238-7140, F ax: (78 1 ) 238-7 1 99

The Fede r a l Aviation Administration (FAA) recei v d yo ur questi o n that you have subm itted via the docket F AA-20 1 0-0068, regardin g the FAA Airworthiness Dir ective ( AD) 2011-02-07.

A fier a careful re v iew of your question
, we have fo
to AD 20 11- 02

- 07.

Please
, find encl o sed the summar y of all public COl regarding this AD wit h the FAA r es pon ses.

Sincerely
,

' {

### ..,."'**'' ~-** **~J<.A.. O,**  

### ''----_

Tomas z Rakowski E n gi n ee r , E n gine Ce rtification Office Fe d era l Aviation Administration nd 

# r

infoml at ion warranting a c hange

llents to AD 2011-02-0 7 and questions

Enclos ur e: Summ ar y of FAA Respons e s to Pub l ic Co mm e nts and Questions Regarding AD 20 11- 02-07 Fi n a l Rul e

- Request for Co mment sU.s. D epartment of Transportation Federal Aviation Administration


### MA'< 1 2 ZO\l Engine and Propeller Oirectorat

Biman Bangladesh Airlines Limited ATTN: Ehsanul Haque Central Engineering Biman Engineering Hangar Comp le x Ha z rat Shahjalal International Airport

. Dhaka
, Bangladesh, 1229

Dear Mr. Haque:

The Federal Aviation Administration (FAA) recei via the docket FAA-2010-0068, regarding the FA 2011-02-07. Engine Certification Office 12 New England Executive Park Burlington, MA 01803 (781) 238-7140
, Fax: (781) 238

- 7199

d Y\lur comment that you have submitted A irWorthiness Directive (AD)

After a careful review of your comment, we have 

### fi un no information warranting a change to AD 2011-02-07.

Please, find enclosed the summary of all public co ne , ts to AD 2011-02-07 and questions regarding this AD with the FAA responses.

Sincerely,

### 1~ Tomasz Rakowski Engineer, Engine Certification Office Federal Aviation Administration

Enclosure: Summary of FAA Responses to Pub ic omments and Questions Regarding AD 2011-02-07 Final Rule

- Reque t fo CommentsU,S, Department of Transp o rtation Federal Aviation Adminis t ration



### MAY 1 2 ZO\1 Engine and Propeller Directorate

Boeing Commercial Airplanes ATTN : Randy Johnstone 3855 N Lakewood Blvd Long Beach, CA 90846

Dear M r. Johnston e: Engine Certification Office 12 New Engla nd E xecutive Park Burlington, MA 01803 (781) 238-7140, Fa x: (781) 238-7199

The Federal Aviation Administration (FAA) receiv d your comment that you have submitted via the docket FAA

- 2010-0068
, regarding the FAA Ainr0rthiness Directive (AD) 2011

- 02-07.

After a careful review of your comment, we h ave D und r o information warranting a change to AD 2011-02-07.

Please, find enclosed the summary of all public co n ments to AD 2011-02-07 and questions regarding this AD with the FAA responses

.

Sincerely
,**~""__ ~_k**  

### ....**~~_** Tomasz Rakowski Engineer, Engine Cert ification Office Federal Aviation Administration

Enclosure: Summary of FAA Responses t o Pub ic Comments and Questions Regarding AD 2011-02-07 Final Rule

- Reque t for CommentsU.S

. Deportment of Transportation Federal Aviation Administration



### MAY 1 2 2011 Engine and Propeller Directorat

Hong Kong Aircraft Engi n ee ri ng Co. Ltd. ATTN: Thomas W

. K. Lai 80 South Perimeter Road HK International Airport Lantau, Hong Kong

Dear Mr. Lai: Engine Certification Office 12 New England Exe cutive Park Burlington
, MA 01803 (781) 238-7140, Fax : (781) 238-7199

The Federal Aviation Administration (FAA) recei d yo u r comments and questions that you have submitted via the docket FAA

- 2010

- 0068, re ardih g t h e FAA Airworthiness Directive (AD) 2011-02-07

.
After a ca r ef u l review of your co mm e nt s, we have ount! no inforn1ation warranting a change
to AD 2011

- 02

- 07.

Please, find enclosed the summary of all public co regarding this AD with the FAA res p onses.

Sincerely,**~ IQ~**  

### (.2=.9..,,-"-, 0_ Tomasz Rakowski E ngineer, Engine Ce rtification Office Federal Aviation Adm ini stra ti on ents to AD 2011 -0 2-07 and questions

Enclos ure: Summary of FAA Responses to Pub ic omments and Questions Re gard in g AD 20 1 1

- 02

- 07 Final Rule

- R e que t fo CommentsSummary of FAA Responses to Public Comments and Questions Regarding AD 2011-02-07 Final Ru le – Request for Comments Page 1 of 5 

### Summary of FAA Responses to Public Comments and Questions Regarding AD 2011-02-07 Final Rule – Request for Comments

Applicability in paragraph (c)(2) Comment: One commenter, Boeing Commercial Airplanes, st ated in docket document FAA-2010-0068-0018 that AD 2011-02-07 was applic able to DC-10 series airplanes equipped with CF6-50 series engines in stalled: DC-10-15, DC-10-30, DC-10-30F, KC-10, KDC-10, and MD-10-30F. FAA Disposition: At this time we are not planning to change paragraph (c)(2) of AD 2011-02-07 to include this comment, as this paragraph is not all-inclusive and is for informational purposed only.
Conditional borescope inspecti on (BSI) of high-pressure turbine (HPT) blades per paragraph (f)(3) Comment: Two commenters proposed via email th at the requirements of paragraph (f)(3) in conjunction with items (iv) and (v ) in Table 2 of AD 2011-02-07 be changed so BSI of HPT blades is required only if an engine experiences two consecutive raw exhaust gas temperature (EGT) trend data points that exceed the EGT levels specified in the AD, and the increase in the raw EGT trend datapoints is not confirmed by a corresponding increase in the raw fuel flow or fan speed/c ore speed (N1/N2) relati onship (e.g. due to an EGT indication error, TAT error, pneumatic loading variations, or unusual altitude operations). FAA Disposition: At this time, we are not planning to change the AD with regards to paragraph (f)(3) requirements. We could however consider an AMOC to AD 2011-02-07, paragraph (f)(3), if requested and substantiate d to show that the level of safety mandated by the AD can be maintained if for certain c onditions the EGT data exceeding the rolling average could be disregarded.
Waiving repetitive engine core vibrati on survey requirements of paragraph (p) Comment: One commenter, Biman Bangladesh Airlines Limited, requested in docket document FAA-2010-0068-0017 the requirements fo r repetitive engine core vibration survey be waived for the operators of ai rcraft equipped with Airborne Vibration Monitoring (AVM) system and performing Engine Condition Trend Monitoring. FAA Disposition: The intent of paragraph (p) of AD 2011-02-07 is for the operator of applicable engines to perform repetitive enginecore vibration surveys regardless of the condition of the engine system, complementary to any engine health programs. At this point, we are not planning to waive or alter the requirements of paragraph (p). However, you may request an AMOC to this paragraph to extend the survey intervals, if you can show that the level of safety mandated by the AD can be maintained with the engine health programs you are performing.
Revising of GE CF6- 50 S/B 72-1313 Revision 1 Comment: One commenter, Hong Kong AircraftEngineering Co. Ltd., proposed in docket document FAA-2010-0068-0011, that GE CF6-50 S/B 72-1313 Revision 1, be revised to recommend repetitive engine core vibration surveys and be incorporated by reference in AD 2011-02-07.Summary of FAA Responses to Public Comments and Questions Regarding AD 2011-02-07 Final Ru le – Request for Comments Page 2 of 5 

### FAA Disposition: Engine manufacturers own their service bulletins. We approve the technical content (data) in those documents . Suggestions regarding alterations to GE service bulletins should be addressed to GE directly. At this time, we are not planning to incorporate GE CF6-50 S/B 72-1313 by refe rence in AD 2011-02-07. This bulletin is referenced in the AD only as guidance for the operators.
Amendment for the FPI requirements Comment: One commenter proposed via email that the FPI of low-pressure turbine (LPT) stage 3 disk forward spacer arm be pe rformed without disassembling the LPT rotor down to piece part level. FAA Disposition: The inner diameter of the installe d LPT stage 3 disk forward spacer arm is not accessible for a proper cleaning and FPI, and therefore requires disassembly of the part from its module/rotor. At this time, we are not planning to amend this requirement.
Requirements for fluorescent penetrant inspec tion (FPI) of the LP T stage 3 disk per paragraph (g) Question: One commenter, Hong Kong AircraftEngineering Co. Ltd., in docket documents FAA-2010-0068-0011 and FAA-2010- 0068-0014, and seven commenters via email, asked what were the pass/fail criteria for BSI of the HPT stage 1 and stage 2 blades required in paragraph (f) of AD 2011-02-07. Response: The intent of paragraph (g) of AD 2011-02-07, is for the operator of applicable engines to perform the FPI of LPT stage 3 disk forward spacer arm inner diameter if the engine fails any of the BS I of HPT rotor stage 1 or stage 2 blades, required by paragraph (f) of this AD. Then, if FPI reveals cracks of band of fluorescence, such disk must be removed from service. The limits for the HPT stage 1 and stage 2 blade borescope inspections are defined in the applicable Airframe Maintenance Manual (AMM). If the Manual does not define limits incertain areas of the airfoil, damage in these areas would not require an action (i.e. FPI of LPT st age 3 disk) per this AD.
Ultrasonic inspection (UI) as means of compliance with paragraph (f) Question: One commenter, Hong Kong Aircraft Engineering Co. Ltd., asked in docket document FAA-2010-0068-0011 if the UI of the LP T stage 3 disk forward spacer arm per General Electric Company (GE) CF6-50 Serv ice Bulletin (S/B) 72-1312 Revision 1 be an acceptable equivalent of the FPI to meet the requirements of AD 2011-02-07. FAA Response: Ultrasonic inspection is not consider ed an acceptable means of meeting the requirements of para graph (f) of this AD.
Limits for BSI per paragraph (f) Question: One commenter, Hong Kong Aircraft Engineering Co. Ltd., asked in docket document FAA-2010-0068-0014 if the BSI pass/fail limit criteria in AD 2010-06-15 were applicable to BSI required by AD 2011-02-07. FAA Response: AD 2010-06-15 was superseded by AD 2010-12-10, which was ultimately superseded by AD 2011-02-07. The requirements of the superseded ADs (i.e. 2010-06-15 and 2010-12-10) are no longer in eff ect. Use the applicable AMM limits forSummary of FAA Responses to Public Comments and Questions Regarding AD 2011-02-07 Final Ru le – Request for Comments Page 3 of 5 

### pass/fail criteria for the borescope insp ection required in paragraph (f) of AD 2011-02-07.
EGT thermocouple probe inspections per paragraphs (h) and (i) Question: One commenter, Hong Kong AircraftEngineering Co. Ltd., in docket document FAA-2010-0068-0011 and one commenter via email asked what was the procedure for EGT thermocouple prob e inspections required by AD 2011-02-07. FAA Response: The intent of paragraphs (h) and (i) of AD 2011-02-07 is for the operator of applicable engine to determine the level of w ear caused by contact between the clocked turbine mid-frame (TMF) liner and the EGT thermocouple probes. The TMF liner clocking inspections per applicable A MM are appropriate inspection procedures to meet the requirements of these paragraphs. A visual inspection of the probe is sufficient, however it would require pulling the probe out of the engine, because a visual check (e.g. via borescope) of the installed probe would notfully show the wear damage. Note that GE CF6-50 S/B 72-1307 Revision 1 calls for ap plicable AMM. All operations for TMF liner clocking inspections must be perf ormed if required by applicable AMM.
EGT system resistance check inspec tions per paragraphs (k) and (l) Question: One commenter, Hong Kong Aircraft Engineering Co. Ltd., asked in docket document FAA-2010-0068-0011 what was the pro cedure for EGT system resistance check inspection required by AD 2011-02-07. FAA Response: AMM applicable to th e airframe should be re ferenced for the EGT system resistance check inspections per paragraphs (k) and (l) of AD 2011-02-07. Note that GE CF6-50 S/B 72-1307 Revision 1 calls for applicable AMM.
Alternate means of meeting re quirements of paragraph (n) Question: One commenter, Hong Kong AircraftEngineering Co. Ltd., in docket document FAA-2010-0068-0011 and four commenters via email asked if the one-time UI of the LPT stage 3 disk forward spac er arm required by AD 2011-02-07 could be accomplished by performing GE CF6-50 S/B 72-1309 Revision 1, and if FPI was equivalent to UI. Moreover, one comment er, Air India, asked in document FAA-2010- 0068-0012 if the one-time ultrasonic inspection of the LPT stage 3 disk forward spacer arm is required if the disk has just beenFPI inspected and is pending installation. FAA Response: The intent of paragraph (n) of AD 2011-02-07 is for the operator of applicable engine to perform, within 75 cycles after the effective date of this AD, a onetime UI of the LPT stage 3 disk forward spacer arm per paragraphs E through K of Appendix A of GE CF6-50 S/B 72-1312 Revision 1. Per paragraph (y) of this AD, this inspection requirement may be satisfied if an UI was performed before the effective date of this AD using paragraphs E through K of Appendix A of SBs No. 72-1312 or 72-1312 Revision 1. The requirements of paragraph (n ) of this AD are not automatically met by accomplishing GE CF6-50 SB 72-1309, i.e. by FPIinspection. You may however request an alternative method of comp liance (AMOC) for the engines that have complied with GE CF6-50 S/B 72-1309 after the 3rd of June, 2010 to satisfy paragraph (n) of this AD. Such an AMOC request may propose performing a piece part level FPI of the LPT stage 3 disk, to satisfy paragraph (n) of this AD.Summary of FAA Responses to Public Comments and Questions Regarding AD 2011-02-07 Final Ru le – Request for Comments Page 4 of 5 

### Alternate means of meeting re quirements of paragraph (r) Question: One commenter, Hong Kong Aircraft Engineering Co. Ltd., asked in docket document FAA-2010-0068-0011 if on-wing UI of LP T stage 3 disk can be performed per GE CF6-50 S/B 72-1312 Revision 1 in stead of FPI to meet requirements of paragraph (r) of this AD. FAA Response: No. A failed engine core vibration survey requires FPI of LPT stage 3 disk forward spacer arm before returning the engine to service.
Engine test cell runs to meetrequirements of paragraph (o) Question: One commenter asked via email if befo re installation after the shop visit the engine core vibration survey requirement of paragraph (o) can be met by the full engine test cell performance run and meeting vibr ation limits per the Engine Manual (EM). FAA Response: The intent of paragraph (o) of AD 2011-02-07 is for the operator of applicable engines to perform an initial engine core vibration survey within 75 cycles after the effective date of this AD with surv ey parameters set as required by paragraphs (o)(1) and (o)(2) of this AD. Per paragraph (z) of this AD, this initial inspection requirement may be satisfied if an engine co re vibration survey was performed before the effective date of this AD using GE CF6-50 S/Bs No. 72-1313 or 72-1313 Revision 1 within engine's last 350 cycles. The requireme nts of paragraph (o) are not automatically met by passing the EM vibration survey in a test cell. You may however request an AMOC for the engines that have been installed onto aircraft after the 3rd of June, 2010, which have passed the EM vibration survey requirements in an approved test cell and have not accumulated any engine flight cycl es nor had a shop visit between subject test cell vibration survey and engi ne installation, to satisfy paragraph (o) of this AD.
Reported vibrations requiring engine co re vibration survey per paragraph (s) Question: One commenter asked via email if there was defined a level of vibrations that would trigger the engine core vibration su rvey per requirements of paragraph (s). FAA Response: The intent of paragraph (s) of AD 2011-02-07 is to perform the engine core vibration survey per para graphs (o)(1) through (o)(2) if the maintenance crew or the flight crew report engine vibrations that are suspected to be caused by the HPT rotor. The indicated core vibration levels are defined in appropriate AMM.
Reporting requirements of paragraph (u) Question: Two commenters asked via email if th e requirements of paragraph (u)(1) for reporting of cracks is applicableto cracks on borescope inspec ted HPT blades, if there is a template for the reports, and if all failed di sks or only cracked disks should be reported. FAA Response: The intent of paragraph (u)(1) of AD 2011-02-07 is to request the operator of applicable engi ne to report any cracks or circumferential bands of fluorescence found on LPT stage 3 disk fo rward spacer arms. Although, there is no required format of such report, it should at least determine engine serial number, affected disk part number and serial number, and cy cles since new and since the last inspection. Note that we also requested reporting of failed UIs of LPT st age 3 disk and failed engine core vibration surveys in paragraphs (u)(2) and (u)(3), respectively.Summary of FAA Responses to Public Comments and Questions Regarding AD 2011-02-07 Final Ru le – Request for Comments Page 5 of 5 

### Previous credit per paragraph (aa) Question: Two commenters asked via email if they were required to perform the initial BSI per paragraph (f)(1) of AD 2011-02-07 if they had been granted AMOCs to AD 2010-12-10 approving extended BSI intervals. FAA Response: Per paragraph (aa) of AD 2011- 02-07, the AMOC to AD 2010-12-10 paragraph (g) that we granted you is still valid. You can use the ex tended cycle intervals for borescope inspections to comply w ith AD 2011-02-07, paragraph (f) requirements. The engines that have been borescope in spected per AD 2010-12-10 paragraph (g) within the last approved extended number of cycles do not need to be "initial" borescope inspected.
AMOC for inspection intervals Question: Two commenters asked via email if extending the inspection intervals of AD 2011-02-07 is possible, and inwhat circumstances. FAA Response: You can request an AMOC to a ny mandatory requirement of AD 2011- 02-07, if you find a different way to comply w ith the actions specified in this AD. We will grant you such AMOC, if your proposal pr ovides an acceptable level of safety. Please, refer to 14 CFR Part 39.19 and F AA Order 8110.103A for details on AMOCs.