Airworthiness directives › 2023-05-17
AD 2023-05-17 Airworthiness Directives; General Electric Company Turbofan Engines
Applicability*9
This AD applies to General Electric Company (GE) GE90-76B, GE90-85B, GE90-90B, and GE90-94B model turbofan engines, excluding those engines with an installed full set of high-pressure turbine (HPT) stage 2 nozzles with part numbers 1847M47G23 and 1847M47G24.
Compliance
Comply with this AD within the compliance times specified, unless already done.
Required actions
(1) Within the compliance times specified in paragraphs (g)(1)(i) and (ii) of this AD, perform an initial borescope inspection (BSI) of the forward platforms of the HPT stage 2 blades, or perform a 360 degree BSI of the leading edges of the HPT stage 2 nozzles (optional procedure) in accordance with the Accomplishment Instructions, paragraph 3.A.(3)(a) of GE GE90 SB 72-1166, Revision 3, dated February 14, 2019 (the SB): (i) For engines with HPT stage 2 nozzles that have accumulated 22,000 or more flight hours since new or since last overhaul as of the effective date of this AD, perform the initial BSI before accumulating 250 flight cycles (FCs) after the effective date of this AD. (ii) For engines with HPT stage 2 nozzles that have accumulated less than 22,000 flight hours since new or since last overhaul as of the effective date of this AD, perform the initial BSI before accumulating 22,000 flight hours since new or since last overhaul, or within 250 FCs after the effective date of this AD, whichever occurs later. (2) Thereafter, at intervals not to exceed 100 FCs from performance of the last BSI of the forward platforms of the HPT stage 2 blades, or at intervals not to exceed 500 FCs from the last BSI of the leading edges of the HPT stage 2 nozzles, as applicable, perform a repetitive BSI of the forward platforms of the HPT stage 2 blades or the leading edges of the HPT stage 2 nozzles in accordance with the Accomplishment Instructions, paragraph 3.A.(3)(a) of the SB. (3) If, during any inspection required by paragraphs (g)(1) or (g)(2) of this AD, rub marks, evidence of contact on the HPT stage 2 blade forward platform on three or more HPT stage 2 blades, or an unserviceable HPT stage 2 nozzle is found, before further flight, remove and replace the HPT stage 2 nozzles with parts eligible for installation. Note 1 to paragraph (g)(3): Serviceability criteria can be found in the GE90 Boeing 777 Aircraft Maintenance Manual, 72-00-00, INSPECTION/CHECK, Subtask 72-00-00-220-074-G00.
Unsafe condition
This AD was prompted by a commanded in-flight shutdown (IFSD) due to cracking and rockback of the HPT stage 2 nozzles resulting in blade liberation, severe rotor imbalance, and liberation of the exhaust centerbody. The FAA is issuing this AD to prevent failure of the HPT stage 2 nozzles, HPT stage 2 blades, and exhaust centerbody. The unsafe condition, if not addressed, could result in IFSD, failure of the engine and exhaust centerbody, and loss of the airplane.
Affected ADs
None.
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