It is just reported on the news that a Japan Airlines 747-400 47 GRU-JFK-NRT landed at Shin Chitose Airport in Hokkaido.
They reported that the cabin pressure dropped dramatically and oxygen masks came up. The plane descended from its flight level to 3000 meters in a matter of minutes and landed safely at Shin Chitose.
I am glad that the 347 pax on the planes were safe and it landed at Shin Chitose. Does anyone know more details on this? Was this another maintenance error or some thing other than that? The ship # was JA8072.