Aircraft Flight Operation Regulations Article 285-14
An airplane when operated in accordance with the instrument flight rules, or when the airplane cannot be maintained in a desired attitude without reference to one or more flight instruments, shall be equipped with Article 248 requirements and 2 independent attitude indicating and calculating systems.
中文原文 航空器飛航作業管理規則第285-14條
飛機依儀器飛航規則飛航，或須依賴一種或多種飛航儀表維持其所需姿態飛航者，除應符合第二百四十八條規定外，應備有二組獨立之高度顯示及計算系統。