T’way Air’s flight TWB/TW201 from Seoul/Incheon to Tokyo/Narita suffered a severe turbulence while approaching to Narita. The aircraft landed safely twenty minutes later. A cabin crew broke her/his right ankle. JTSB launched an investigation as an aircraft accident on 3rd May. Just after this accident, an Alitalia Boeing 777 also encountered a turbulence. PROBABLE CAUSES In this accident, it is highly probable that the Aircraft was shaken by severe atmospheric disturbance it encountered during the descent, which caused Flight Attendant A who was ensuring safety in the cabin to lose her balance after feeling like floating and fall down severely backward, which resulted in her injury in the right ankle METAR data at Narita (accident time 09:55 LT/00:55 UTC): RJAA 020100Z 23003KT 180V260 9999 FEW013 BKN050 18/14 Q1005 NOSIG RMK 1CU013 7SC050 A2969= TEMP upper air data at Tateno (40km northwest from Narita): TTAA 02001 47646 99001 18240 20003 00037 17450 21001 92696 11426 25008 85397 07040 29008 70968 02556 25521 50555 18360 23538 40718 29179 23048 30920 36976 23572 25044 429// 23567 20193 477// 24064 15380 527// 23554 10636 633// 23539 88999 66290 23577 31313 73508 82330= TTBB 02008 47646 00001 18240 11890 09240 22832 05636 33724 01528 44718 00756 55676 04357 66612 10150 77598 11359 88589 10772 99546 12771 11441 27357 22429 28566 33421 26779 44326 33978 55300 37176 66279 40173 77216 473// 88128 565// 99102 639// 21212 00001 20003 11992 23003 22915 25509 33876 28508 44836 28509 55798 25010 66666 26024 77577 24030 88521 23538 99404 23048 11306 23569 22290 23577 33245 23566 44216 23568 55137 23550 66115 23038 77100 23539 31313 73508 82330=