Split duct pressure is a condition in which the duct pressure on one side, as shown on the dual duct pressure indicator, is either lower or higher than the duct pressure on the other side with the engines as the bleed source. Duct pressure splits can occur during both normal and abnormal operation of the engine bleed systems. The procedures in this task will enable you to determine if a fault exists in either the left or right pneumatic system based on information from the pilot report or knowledge of the pneumatic system pressure at specific engine N1 speeds and aircraft altitudes.
There are no system controls to regulate both systems to a common pressure so an acceptable split in duct pressure cannot be specified. Each system regulates duct pressure independent from the other when the isolation valve is closed and should be evaluated based on the engine N1, not compared to the other duct pressure. FIM 36–10 T ask Support Figure 305 defines the 9th stage regulated pressure as 32 ± 6 psig and 5th stage regulated presure as 42 ± 8 psig.