Monitoring and alerting distinguishes RNP from all other procedures - making it the most useful navigation tool available today. RNP procedures are designed with multiple layers of protection ensuring the continuity and safety of operations. The probability that an RNP-equipped aircraft will deviate from required navigation performance levels resulting in an alert is extremely remote. Like RNAV, RNP permits aircraft to follow pre-determined paths through the sky. However, RNP has the significant advantage of constant navigation performance monitoring, alerting the crew if the position estimate is insufficiently precise for the procedure being flown. The alert delivered by RNP is similar in concept to the ILS "OFF" flag that warns crews of a problem with an ILS signal. Crews flying RNAV procedures, on the other hand, may not recognize a navigation error until air traffic control or their ground proximity alerting system advises them. | 
