Explain the practical difference between RNP and RNAV procedures.

The practical difference between RNP (Required Navigation Performance) and RNAV (Area Navigation) procedures lies primarily in the requirements for onboard performance monitoring and alerting. Both RNP and RNAV allow aircraft to fly on any desired flight path within the coverage of ground- or space-based navigation aids, or within the limits of the capability of self-contained aids. RNAV is a general term for flying a desired path, whereas RNP includes a specific requirement for the aircraft's navigation system to monitor its actual performance against the required performance, and to alert the pilot if the required performance is not met or cannot be assured. Specifically, RNP procedures require the aircraft to have onboard performance monitoring and alerting capabilities. This means that the aircraft's navigation system must be able to continuously verify that it is meeting the required navigation accuracy for the procedure. If the aircraft's actual navigation performance degrades beyond the specified limits, the system must alert the pilot, allowing them to take corrective action. For example, an RNP approach to an airport might require the aircraft to maintain its position within 0.3 nautical miles of the intended flight path 95% of the time. The aircraft's system monitors this and alerts the pilot if the accuracy degrades beyond that limit. In contrast, RNAV procedures do not necessarily require onboard performance monitoring and alerting. While RNAV systems provide enhanced navigation capabilities, they may not actively monitor and alert the pilot to deviations from the required performance. This means that the pilot is primarily responsible for ensuring the aircraft remains on the intended flight path. Because of the performance monitoring and alerting, RNP procedures typically allow for tighter spacing between routes and lower minimums during instrument approaches compared to RNAV procedures. Therefore, the key practical difference is that RNP mandates onboard performance monitoring and alerting, providing a higher level of safety and precision compared to RNAV, which relies more on pilot monitoring.