Airworthiness Directive · Amendment 39-16930 · General Electric Company Turbofan Engines
General Electric Company Turbofan Engines
Superseded. A later AD replaced this one: AD 2023-04-11. Comply with the one in force.
This AD applies to General Electric Company (GE) CF6-45A, CF6-45A2, CF6-50A, CF6-50C, CF6-50CA, CF6-50C1, CF6-50C2, CF6-50C2B, CF6-50C2D, CF6-50E, CF6-50E1, CF6-50E2, and CF6-50E2B turbofan engines, including engines marked on the engine data plate as CF6-50C2-F and CF6-50C2-R, with any of the low-pressure turbine (LPT) rotor stage 3 disk part numbers listed in Table 1 of this AD installed.
| 9061M23P06 | 9061M23P07 | 9061M23P08 | 9061M23P09 | 9224M75P01 |
| 9061M23P10 | 1473M90P01 | 1473M90P02 | 1473M90P03 | 1473M90P04 |
| 9061M23P12 | 9061M23P14 | 9061M23P15 | 9061M23P16 | 1479M75P01 |
| 1479M75P02 | 1479M75P03 | 1479M75P04 | 1479M75P05 | 1479M75P06 |
| 1479M75P07 | 1479M75P08 | 1479M75P09 | 1479M75P11 | 1479M75P13 |
| 1479M75P14 | N/A | N/A | N/A | N/A |
We are superseding two existing airworthiness directives (ADs) for General Electric Company (GE) CF6-45 and CF6-50 series turbofan engines with certain low-pressure turbine (LPT) rotor stage 3 disks installed. The existing ADs currently require inspections of high- pressure turbine (HPT) and LPT rotors, engine checks, and vibration surveys. This new AD retains the requirements of the two ADs being superseded, adds an optional LPT rotor stage 3 disk removal after a failed HPT blade borescope inspection (BSI) or a failed engine core vibration survey, establishes a new lower life limit for the affected LPT rotor stage 3 disks, and requires removing these disks from service at times determined by a drawdown plan. This AD was prompted by the determination that a new lower life limit for the LPT rotor stage 3 disks is necessary. We are issuing this AD to prevent critical life- limited rotating engine part failure, which could result in an uncontained engine failure and damage to the airplane.
For the BSIs required by paragraphs (f)(1), (f)(2), and (f)(3) of this AD, inspect the blades from the forward and aft directions. Inspect all areas of the blade airfoil. Your inspection must include blade leading and trailing edges and their convex and concave airfoil surfaces. Inspect for signs of impact, cracking, burning, damage, or distress.
(1) Perform an initial BSI of the HPT rotor stage 1 and stage 2 blades within 10 cycles after the effective date of this AD.
(2) Thereafter, repeat the BSI of the HPT rotor stage 1 and stage 2 blades within every 75 cycles since last inspection (CSLI).
(3) Borescope-inspect the HPT rotor stage 1 and stage 2 blades within the cycle limits after the engine has experienced any of the events specified in Table 2 of this AD.
(4) Remove any engine from service before further flight if the engine fails any of the BSIs required by this AD.
| If the engine has experienced: | Then borescope-inspect: |
|---|---|
| (i) An exhaust gas temperature (EGT) above redline. | Within 10 cycles. |
| (ii) A shift in the smoothed EGT trending data that exceeds 18 °F (10 °C), but is less than or equal to 36 °F (20 °C) | Within 10 cycles. |
| (iii) A shift in the smoothed EGT trending data that exceeds 36 °F (20 °C) | Before further flight. |
| (iv) Two consecutive raw EGT trend data points that exceed 18 °F (10 °C), but is less than or equal to 36 °F (20 °C), above the smoothed average | Within 10 cycles. |
| (v) Two consecutive raw EGT trend data points that exceed 36 °F (20 °C) above the smoothed average | Before further flight. |
For those engines that fail any BSI requirements of this AD, before returning the engine to service:
(1) Remove the LPT rotor stage 3 disk from service; or
(2) Perform a fluorescent-penetrant inspection (FPI) of the inner diameter surface forward cone body (forward spacer arm) of the LPT rotor stage 3 disk as specified in paragraphs (l)(1)(i) through (l)(1)(iii) of this AD.
(1) Inspect the EGT thermocouple probe for damage within 50 cycles after the effective date of this AD or before accumulating 750 CSLI, whichever occurs later.
(2) Thereafter, re-inspect the EGT thermocouple probe for damage within every 750 CSLI.
(3) If any EGT thermocouple probe shows wear through the thermocouple guide sleeve, remove and replace the EGT thermocouple probe before further flight, and ensure the turbine mid-frame liner does not contact the EGT thermocouple probe.
(1) Perform an EGT system resistance check within 50 cycles from the effective date of this AD or before accumulating 750 cycles since the last resistance check on the EGT system, whichever occurs later.
(2) Thereafter, repeat the EGT system resistance check within every 750 cycles since the last resistance check.
(3) Remove and replace, or repair any EGT system component that fails the resistance system check before further flight.
Within 75 cycles after the effective date of this AD, perform a UI of the forward spacer arm of the LPT rotor stage 3 disk. Use Appendix A of GE Service Bulletin (SB) No. CF6-50 S/B 72-1312, Revision 1, dated October 18, 2010, paragraph 4. except for paragraph 4.(12), to do the UI.
(1) Within 75 cycles after the effective date of this AD, perform an initial engine core vibration survey.
(2) Use about a one-minute acceleration and a one-minute deceleration of the engine between ground idle and 84% N2 (about 8,250 rpm) to perform the engine core vibration survey.
(3) Use a spectral/trim balance analyzer or equivalent to measure the N2 rotor vibration.
(4) If the vibration level is above 5 mils Double Amplitude then, before further flight, remove the engine from service.
(5) For those engines that fail any engine core vibration survey requirements of this AD, then before returning the engine to service:
(i) Remove the LPT rotor stage 3 disk from service; or
(ii) Perform an FPI of the inner diameter surface forward spacer arm of the LPT rotor stage 3 disk as specified in paragraphs (l)(1)(i) through (l)(1)(iii) of this AD.
(6) Thereafter, within every 350 cycles since the last engine core vibration survey, perform the engine core vibration survey as required in paragraphs (k)(1) through (k)(5) of this AD.
(7) If the engine has experienced any vibration reported by maintenance or flight crew that is suspected to be caused by the engine core (N2), perform the engine core vibration survey as required in paragraphs (k)(1) through (k)(5) of this AD within 10 cycles after the report.
(8) Vibration surveys carried out in an engine test cell as part of an engine manual performance run fulfill the vibration survey requirements of paragraphs (k)(2) through (k)(3) of this AD.
(1) At the next shop visit after the effective date of this AD:
(i) Clean the LPT rotor stage 3 disk forward spacer arm, including the use of a wet-abrasive blast, to eliminate residual or background fluorescence.
(ii) Perform an FPI of the LPT rotor stage 3 disk forward spacer arm for cracks and for a band of fluorescence. Include all areas of the disk forward spacer arm and the inner diameter surface forward spacer arm of the LPT rotor stage 3 disk.
(iii) Remove the disk from service before further flight if a crack or a band of fluorescence is present.
(2) Thereafter, clean and perform an FPI of the LPT rotor stage 3 disk forward spacer arm, as specified in paragraphs (l)(1)(i) through (l)(1)(iii) of this AD, at each engine shop visit that occurs after 1,000 cycles since the last FPI of the LPT rotor stage 3 disk forward spacer arm.
Remove LPT rotor stage 3 disks listed in Table 1 from service as follows:
(1) For disks that have fewer than 3,200 flight cycles since new (CSN) on the effective date of this AD, remove the disk from service before exceeding 6,200 CSN.
(2) For disks that have 3,200 CSN or more on the effective date of this AD, do the following:
(i) If the engine has a shop visit before the disk exceeds 6,200 CSN, remove the disk from service before exceeding 6,200 CSN.
(ii) If the engine does not have a shop visit before the disk exceeds 6,200 CSN, remove the disk from service at the next shop visit after 6,200 CSN, not to exceed 3,000 cycles from the effective date of this AD.
(1) After the effective date of this AD, do not install or reinstall in any engine any LPT rotor stage 3 disk that exceeds the new life limit of 6,200 CSN.
(2) Remove from service any LPT rotor stage 3 disk that is installed or re-installed after the effective date of this AD, before the disk exceeds the new life limit of 6,200 CSN.
(1) For the purposes of this AD, an EGT above redline is a confirmed over-temperature indication that is not a result of EGT system error.
(2) For the purposes of this AD, a shift in the smoothed EGT trending data is a shift in a rolling average of EGT readings that can be confirmed by a corresponding shift in the trending of fuel flow or fan speed/core speed (N1/N2) relationship. You can find further guidance about evaluating EGT trend data in GE Company Service Rep Tip 373 ”Guidelines For Parameter Trend Monitoring.”
(3) For the purposes of this AD, an engine shop visit is the induction of an engine into the shop after the effective date of this AD, where the separation of a major engine flange occurs; except the following maintenance actions, or any combination, are not considered engine shop visits:
(i) Induction of an engine into a shop solely for removal of the compressor top or bottom case for airfoil maintenance or variable stator vane bushing replacement.
(ii) Induction of an engine into a shop solely for removal or replacement of the stage 1 fan disk.
(iii) Induction of an engine into a shop solely for replacement of the turbine rear frame.
(iv) Induction of an engine into a shop solely for replacement of the accessory gearbox or transfer gearbox, or both.
(v) Induction of an engine into a shop solely for replacement of the fan forward case.
(4) For the purposes of this AD, a raw EGT trend data point above the smoothed average is a confirmed temperature reading over the rolling average of EGT readings that is not a result of EGT system error.
(1) A BSI performed before the effective date of this AD using AD 2010-06-15, Amendment 39-16240 (75 FR 12661, March 17, 2010) or AD 2010-12-10, Amendment 39-16331 (75 FR 32649, June 9, 2010) or AD 2011-02-07, Amendment 39-16580 (76 FR 6323, February 4, 2011) within the last 75 cycles, satisfies the initial BSI requirement in paragraph (f)(1) of this AD.
(2) A UI performed before the effective date of this AD using AD 2011-02-07, Amendment 39-16580 (76 FR 6323, February 4, 2011) or GE SB No. CF6-50 S/B 72-1312, dated August 9, 2010 or GE SB No. CF6-50 S/B 72-1312 Revision 1, dated October 18, 2010, satisfies the inspection requirement in paragraph (j) of this AD.
(3) An engine core vibration survey performed before the effective date of this AD using AD 2011-02-07, Amendment 39-16580 (76 FR 6323, February 4, 2011) or GE SB No. CF6-50 S/B 72-1313, dated August 9, 2010 or GE SB No. CF6-50 S/B 72-1313 Revision 1, dated October 18, 2010, within the last 350 cycles, satisfies the initial survey requirement in paragraphs (k)(1) through (k)(5) of this AD.
(4) An FPI of the LPT rotor stage 3 disk forward spacer arm performed before the effective date of this AD using AD 2011-18-01, Amendment 39-16783 (75 FR 52213, August 22, 2011), within the last 1,000 flight cycles of the LPT rotor stage 3 disk, satisfies the initial inspection requirements in paragraphs (l)(1)(i) through (l)(1)(iii) of this AD.
