An aircraft includes one or more engines configured to generate high-pressure bleed air and low-pressure bleed air. An aircraft environmental control system (ECS) is in fluid communication with one or more of the engines to receive the high-pressure bleed air and the low-pressure bleed air. The ECS calculates a synthesized low-pressure value associated with the low-pressure bleed air while still providing bleed air using the high pressure bleed air. The ECS further switches from the high pressure bleed air to the low-bleed pressure air through the ECS while blocking flow of the high-pressure bleed air through the ECS based on the synthesized low-pressure value.