Japan Airlines

1. Table 1 defines compliance criteria. And 2. (g) (1) (i) defines initial inspection compliance for V2525-D5 and V2528-D5. (i) says Inspect within 1,000 operating hours after the engine meets all　criteria as defined in Table 1 of this AD, or within 600 operating hours after the effective date of this AD, which ever is greater. Usually Takeoff EGT margin is captured automatically and sent to ground station by ACARS then stored in operator’s engine data monitoring database. Some operator does not have this kind of EGT margin capture capability. JAL currently does not have EGT margin capture system. To set up EGT margin capture system is burden for operators and costly. This AD does not consider the situation where operators do not have EGT margin capture capability. At least AD should define initial threshold like 5,000hours + 600hours = 5600hours (stage 1 blade outer air seal segments hour since new or since last repair) This initial threshold should not depend on EGT margin condition. Repetitive inspection interval is 1000 operating hours. Another option is to check EGT margin manually every one month and inspect within 1000 operating hours after the engine meets all criteria as defined in Table 1 or within 600 operating hours after the effective date of this AD, whichever is greater. Repetitive inspection interval is 1000 operating hours. To check EGT margin manually every day is big burden. 2. NPRM 2. (h) define Exhaust Gas Temperature Margin. This generic definition does not include air speed nor air bleed configuration. This is beneficial for operators because if the AD defines more detail condition for Exhaust Gas temperature Margin, operator must modify their EGT capture system. 3. The attached pictures show JAL’s V2525-D5 BOAS condition. Engine S/N V20210 have accumulated 5161 cycles, Engine S/N V20124 have accumulated 8895 cycles but BOAS condition is very good. We believe the engine, which have experienced the HPT case burnthrough or the HPT case bulging were exposed to very sever operating condition such as sandy or very hot environment. We believe corrective action should be established each operator’s operational environment. 4. Table 1　defines same EGT margin value for A1, A5 and D5. EGT margin= EGT redline – EGT. EGT redline are different for each model. Low EGT redline engine like D5 must start inspection earlier than high EGT redline engine. Since hardware is same for A1, A5 and D5, we believe this AD intention is to start this inspection when EGT reaches a specific metal melting temperature. Therefore EGT margin should vary based on EGT redline/thrust level. 5. Table 1 defines EGT margin value 45 celsius degree, we believe this is too large of a margin. This margin should be smaller. 6. Table 1 defines for A1, A5 and D5 compliance. D5 compliance is much severe than A1 and A5. This kind of HPT deterioration could happen on high thrust engine in general. Therefore table should be categorized based on thrust level.