During flight, which bleed air is primarily used for operating the boots?

The operation of aircraft boots, which are used for ice protection, primarily utilizes P2.5 bleed air. This specific bleed air source is an intermediate pressure that strikes a balance between the higher pressures from P3 and the lower pressures from P2. The P2.5 pressure is ideal for the operation of boots because it provides sufficient pressure to inflate and deflate the boots effectively without causing damage to the system or compromising its operation.

In contrast, P3 bleed air generally comes from the engine compressor and is high pressure, whereas P2 bleed air is at a lower pressure level and might not be sufficient for driving the ice protection system. P1 bleed air refers to bleed air from a lower stage and does not serve the purpose of inflating the ice boots. Thus, P2.5 is uniquely positioned in the bleed air hierarchy to provide the optimal pressure for this critical function.