When the CKPT ALT light is illuminated, what delta P is expected?

When the CKPT ALT light is illuminated, it indicates that there is an issue with cockpit pressure that does not meet the normal operational limits. Specifically, this light typically illuminates when the differential pressure (delta P) in the cockpit is less than a critical threshold.

The expected delta P when the CKPT ALT light is illuminated is less than 3.4 psi. This means that the cabin pressure is not rising adequately or is falling when compared to the ambient pressure outside the aircraft. This situation is crucial for pilot awareness as it can affect safety, and awareness of the pressure conditions ensures that the pilot can take necessary actions—like confirming pressure altitude or descending to a safer altitude if needed.

Understanding the context of this information is important in flight operations, particularly when dealing with cabin pressurization systems in aircraft, as it directly relates to the safety and performance of the flight operation.