AD 2023-04-11 Airworthiness Directives; General Electric Company Turbofan Engines

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 model turbofan engines, including engines marked on the engine data plate as CF6-50C2-F and CF6-50C2-R, with an installed low-pressure turbine (LPT) rotor stage 3 disk having a part number listed in Table 1 to paragraph (c) of this AD. Table 1 to Paragraph ( c )—Applicable LPT Rotor Stage 3 Disk Part Numbers           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

Comply with this AD within the compliance times specified, unless already done.

(1) Borescope Inspections (BSI) of High-Pressure Turbine (HPT) Rotor Stage 1 and Stage 2 Blades. For the BSIs required by paragraphs (g)(1)(i) through (iii) of this AD, inspect the blades from the forward and aft directions. Inspect all areas of the blade airfoil. The inspection must include blade leading and trailing edges and their convex and concave airfoil surfaces. Inspect for signs of impact, cracking, burning, damage, and distress. (i) Within 75 cycles since last inspection (CSLI) or before further flight, whichever occurs later, perform an initial BSI of the HPT rotor stage 1 and stage 2 blades. (ii) Thereafter, within every 75 CSLI, repeat the BSI of the HPT rotor stage 1 and stage 2 blades. (iii) Within the cycle limits after the engine has experienced any of the events specified in Table 2 to paragraph (g)(1)(iii) of this AD, perform a BSI of the HPT rotor stage 1 and stage 2 blades. Table 2 to Paragraph ( g )(1)( iii )—Conditional BSI Criteria If the engine has experienced: Then borescope inspect: An exhaust gas temperature (EGT) above redline Within 10 cycles. 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. A shift in the smoothed EGT trending data that exceeds 36 °F (20 °C) Before further flight. Two consecutive raw EGT trend data points that exceed 18 °F (10 °C), but are less than or equal to 36 °F (20 °C), above the smoothed average Within 10 cycles. Two consecutive raw EGT trend data points that exceed 36 °F (20 °C) above the smoothed average Before further flight. (iv) If the engine fails any of the BSIs required by this AD, before further flight, remove the engine from service. (2) Engines with Damaged HPT Rotor Blades, For those engines that fail any BSI requirements of this AD, before returning the engine to service, accomplish the actions required by paragraph (g)(2)(i) or (ii) of this AD: (i) Remove the LPT rotor stage 3 disk from service; or (ii) 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 (g)(6)(i)(A) through (C) of this AD. (3) EGT Thermocouple Probe Inspections. (i) Within 750 CSLI, or before further flight, whichever occurs later, inspect the EGT thermocouple probe for damage. Note 1 to paragraph (g)(3)(i): Damage to the EGT thermocouple probe may be indicated by wear through the thermocouple guide sleeve or contact between the turbine mid-frame liner and the EGT thermocouple probe. (ii) Thereafter, within every 750 CSLI, re-inspect the EGT thermocouple probe for damage. (iii) If any EGT thermocouple probe shows wear through the thermocouple guide sleeve or contact between the turbine mid-frame liner and the EGT thermocouple probe, before further flight, remove and replace the EGT thermocouple probe and ensure the turbine mid-frame liner does not contact the EGT thermocouple probe. (4) EGT System Resistance Checks. (i) Within 750 cycles since the last resistance check on the EGT system or before further flight, whichever occurs later, perform an EGT system resistance check. (ii) Thereafter, within every 750 cycles since the last resistance check, repeat the EGT system resistance check. (iii) If an EGT system component fails the resistance system check, before further flight, remove and replace, or repair the EGT system component. (5) Engine Core Vibration Survey. (i) Within 350 cycles since the last engine core vibration survey or before further flight, whichever occurs later, perform an initial engine core vibration survey. (ii) 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. (iii) Use a spectral/trim balance analyzer or equivalent to measure the N2 rotor vibration. (iv) If the vibration level is above 5 mils Double Amplitude, before further flight, remove the engine from service. (v) For those engines that fail any engine core vibration survey requirements of this AD, before returning the engine to service: (A) Remove the LPT rotor stage 3 disk from service; or (B) Perform an FPI of the inner diameter surface forward spacer arm of the LPT rotor stage 3 disk as specified in paragraph (g)(6)(i)(A) through (C) of this AD. (vi) Thereafter, within every 350 cycles since the last engine core vibration survey, perform the engine core vibration survey as required in paragraphs (g)(5)(i) through (v) of this AD. (vii) If the engine has experienced any vibration reported by maintenance or flight crew that is suspected to be caused by the engine core (N2), within 10 cycles after the report, perform the engine core vibration survey as required in paragraphs (g)(5)(i) through (v) of this AD. (viii) Vibration surveys carried out in an engine test cell as part of an engine manual performance run fulfill the vibration survey requirements of paragraphs (g)(5)(ii) and (iii) of this AD. (6) Initial and Repetitive FPI of LPT Rotor Stage 3 Disk. (i) At the next shop visit after accumulating 1,000 cycles since the last FPI of the LPT rotor stage 3 disk forward spacer arm or before further flight, whichever occurs later: (A) Clean the LPT rotor stage 3 disk forward spacer arm, including the use of a wet-abrasive blast, to eliminate residual or background fluorescence; (B) 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; and (C) If a crack or a band of fluorescence is present, before further flight, remove the disk from service. (ii) Thereafter, at each engine shop visit that occurs after accumulating 1,000 cycles since the last FPI of the LPT rotor stage 3 disk forward spacer arm, clean and perform an FPI of the LPT rotor stage 3 disk forward spacer arm, as specified in paragraph (g)(6)(i)(A) through (C) of this AD. (7) Removal of LPT Rotor Stage 3 Disk. (i) For any installed LPT rotor stage 3 disk having a part number listed in Table 1 to paragraph (c) of this AD, at the first occurrence of any one of the conditions identified in paragraphs (g)(7)(i)(A) through (C) of this AD, remove the LPT rotor stage 3 disk from service and replace with LPT rotor stage 3 disk part number 2453M80P01. (A) For a disk that has accumulated fewer than 3,200 cycles since new (CSN) as of March 6, 2012 (the effective date of AD 2012-02-07), remove the disk from service before accumulating 6,200 CSN. (B) For a disk that accumulated 3,200 or more CSN as of March 6, 2012 (the effective date of AD 2012-02-07), do the actions required by paragraphs (g)(7)(i)(B)(1) or (2) of this AD, as applicable to your engine. (1) If the engine has a shop visit before the disk accumulates 6,200 CSN, remove the disk from service at that shop visit. (2) If the engine does not have a shop visit before the disk accumulates 6,200 CSN, remove the disk from service at the next shop visit after accumulating 6,200 CSN, not to exceed 3,000 cycles from March 6, 2012 (the effective date of AD 2012-02-07). (C) Before exceeding 18 months from the effective date of this AD.

This AD was prompted by the occurrence of four events of separation of the LPT rotor assembly, occurring after the effective date of AD 2012-02-07, which resulted in the LPT rotor assembly departing the rear of the engine. The FAA is issuing this AD to prevent critical life-limited rotating engine part failure. The unsafe condition, if not addressed, could result in an uncontained engine failure and damage to the airplane.

This AD replaces AD 2012-02-07, Amendment 39-16930 (77 FR 4650, January 31, 2012) (AD 2012-02-07).