Return air bellow connection with frame ( Duct ) As per RDSO Drawing No. RDSO/ PE/ SK/ AC/ 0069- 2004 ( Rev. 3 ) for RMPU of LHB type AC coaches. Duct Made of META ARAMID/ PARA ARAMID FABRIC with Silicon Rubber Coating on both side as per RDSO Spec. No. RDSO/ PE/ SPEC/ 0197- 2020 ( Rev.- 0 )