Railcars BDtdx,  called BFalm in the 60s and 70s,  are a series of four-axle second-class high-capacity passenger coaches  with post office of the Czech Railways park. All these cars were manufactured for the Czechoslovak State Railways in 1958–1969 in the factory Vagonka Studenka. The cars were to be designed as a trailer to motor railcars 820, but used with other DMU (830, 850, 842 etc)