Area navigation
This domain tests RNAV operations: how waypoints and legs are coded and flown, how navigation specifications are applied, and how on-board performance monitoring changes what you may fly.
Concepts
- RNAV allows flight on any desired path within the coverage of the navigation infrastructure. PBN adds a navigation specification with defined accuracy, integrity and functionality.
- Common specifications are RNAV 10, RNAV 5, RNAV 2, RNAV 1, RNP 4, RNP 1, RNP APCH and RNP AR APCH. For RNP specifications, containment is twice the accuracy value, and the aircraft must monitor performance and alert the crew when it is exceeded.
- Waypoints are fly-by (turn anticipation) or fly-over (no anticipation). Radius-to-fix legs are only available with RNP AR authority, as are RNP values below 0.3 and missed approach paths requiring special design.
Worked example
An aircraft cleared on an RNP 1 route shows ANP 0.8 nm. Since 0.8 nm is less than the 1.0 nm specification, the aircraft is within the navigation specification and may continue. If ANP rises above 1.0 nm, the system alerts and the crew must not rely on the path for separation; they must notify ATC and revert to an alternative navigation method or procedure.
Traps
- Assuming CDI sensitivity is fixed in nautical miles; it scales with phase of flight and specification.
- Flying RNP AR approaches on an ordinary instrument rating - special aircraft and crew approval is required.
- Confusing ANP with RNP accuracy when deciding whether the path is still valid.
- Selecting a direct-to that cuts a fly-by turn and busts protected airspace.