Actually I'm trying to book the HKG-PEK flight in business with Air China. There are 6 daily AC flights flying with aircraft types 321, 744, 777, 772 and two 32Ms. I guess "32M" is A321 with business & economy cabins (without first class), and "321" should be A321 with first & economy cabins (without business) since when i try to book business, "321" plane is not available. Besides, the business class for M32 is from role 1 to 4, starting from role 5 is economy.