AD 2008-03-09 Airworthiness Directives; CFM International, S.A. CFM56-7B Series Turbofan Engines

This AD applies to CFM International, S.A. CFM56-7B18, -7B20, -7B22, -7B24, -7B26, -7B27, -7B22/B1, -7B24/B1, -7B26/B1, -7B27/B1, -7B22/B2, -7B26/B2, -7B27/B3 turbofan engines with turbine rear frame (TRF), part numbers 340-166-205-0, 340-166-206-0, 340-166-207-0, 340-166-208-0, 340-166-209-0, and 340-166-210-0, installed. These engines are installed on, but not limited to, Boeing 737 series airplanes.

You are responsible for having the actions required by this AD performed within 30 days after the effective date of this AD, unless the actions have already been done. Mandatory Inspections (f) Within the next 30 days after the effective date of this AD, revise the applicable inspection program for the Business Jet and Air Carrier engine models by adding the Mandatory Inspection Intervals as specified in this AD, and revise the Airworthiness Limitations Section (ALS) (chapter 05-21-03) of the CFM56-7B Engine Shop Manual, CFMI-TP-SM.10 by adding the following: TURBINE REAR FRAME WITH TANGENTIAL STRUTS—MANDATORY INSPECTIONS—LIFE LIMITS TASK 05-21-03-200-001 1. General A. This section contains the FAA and EASA mandatory Eddy Current inspection intervals for the turbine rear frame with tangential struts. The inspection uses: —A threshold limit, specified in flight cycles —Inspection intervals, specified in flight cycles B. The threshold limit is the timing of the first required inspection. First inspection must be done before that part has reached the threshold number of flight cycles. C. The inspection intervals specify the timing of inspections to be done after the threshold inspection has been reached. Inspections are repetitive without any limit. 2. Mandatory Inspection Intervals for the Critical Areas of the Turbine Rear Frame with Tangential Struts (4 Mount Struts, No. 1, 2, 15, and 16) . C. Turbine Rear Frame Part Numbers 340-166-205-0, 340-166-206-0, 340-166-207-0, 340-166-208-0, 340-166-209-0, 340-166-210-0, for all CFM56-7B SAC engine models (except -7B27A engine models). Refer to figure 805.   Figure index No. Inspection location Inspection threshold (cycles since new) Inspection intervals (cycles) Inspection reference 805 Strut/outer ring fillet radius on trailing edge (A) 25,000 * for -7B SAC (except business jet) engine models Refer to Figure 806 * for -7B SAC (except business jet) engine models Refer to SB 72-0579.*   Strut/hub fillet radius on leading edge (B) 19,000 * for -7B SAC business jet engine models Refer to Figure 807 * for -7B SAC business jet engine models   Strut/outer ring fillet radius on trailing edge (C1 below outer ring)   Strut/outer ring fillet radius on trailing edge (C2 above outer ring) Note: * Applicable to all inspection locations. If inspection is not performed, part must be removed. BILLING CODE 4910-13-P ER04FE08.000 ER04FE08.001 ER04FE08.002 (g) After the effective date of this AD, we will not approve any alternative inspection intervals for these parts except as provided for in paragraph (j) of this AD. TRFs With Unknown Cycles (h) If you cannot establish the number of cycles accumulated since new, remove or inspect the TRF within 300 cycles-in-service after the effective date of this AD. The CFM56-7B Engine Shop Manual (ESM) or air carrier's approved continuous airworthiness maintenance program (CAMP) contains information for inspecting the TRF. (i) You may install a TRF removed in paragraph (h) of this AD after the TRF passes an initial inspection for cracks. The CFM56-7B ESM or CAMP contains information on inspecting the TRF. Alternative Methods of

This AD results from a refined lifing analysis by the engine manufacturer that shows the need to identify an initial threshold for inspecting certain TRFs. We are issuing this AD to prevent failure of the TRF from low-cycle fatigue cracks. Failure of the TRF could result in engine separation from the airplane, which could lead to loss of control of the airplane.