Split duct pressure is a condition in which the duct pressure on one side, as shown on the dual
pressure indicator, is either lower or higher than the duct pressure on the other side when the
APU is the only bleed source and the isolation valve is open. When the APU BLEED switch is
ON and the isolation valve is open, the duct pressure in the left and right pneumatic manifolds
should be the same. The left and right pneumatic pressure indication systems should indicate
the actual duct pressures within a tolerance of plus/minus 2 psi. However, when the left and
right systems are pressurized by only the APU bleed air, the maximum duct pressure indication
difference (split) between the left and right indication systems is 3 psi