Description

The airplane was takeoff from Taoyuan International Airport at 1044 local time. At time 1054, the airplane reached altitude about 20,800ft, left outflow valve failed with "outflow vlv L" EICAS advisory msg. Pilot checked the cabin altitude about 8,600 ft and climb rate 1,200 fpm. Pilot attempted to perform "outflow vlv L" procedure IAW QRH, but immediately followed "Cabin Altitude" warning msg. The pilot donned oxygen mask and performed emergency descent procedure. The airplane turned back and landed safely at Taoyuan International Airport about 1128 local time without person injured. The passenger emergency oxygen was manually deployed.

The highest cabin altitude was about 12,000 ft according to pilot statement.