GNSS and Area Navigation (RNAV, RNP)
GNSS (GPS, GLONASS, Galileo, BeiDou) provides position, navigation and timing. Candidates must understand the space, control and user segments, and the concepts of accuracy, integrity, availability and continuity. Know the augmentation systems: ABAS (aircraft-based), SBAS (satellite-based, e.g. EGNOS, WAAS) and GBAS (ground-based). Understand RAIM (receiver autonomous integrity monitoring) and its role in detecting faults, and the difference between RNAV and RNP: RNP requires on-board performance monitoring and alerting.
Know the PBN concepts, the navigation specifications (RNAV 5, RNAV 1, RNP 1, RNP 0.3, RNP 4, RNP 10), and the meaning of the performance requirement (accuracy, integrity, continuity, availability). Understand that GNSS is line-of-sight to satellites and is affected by ionospheric, tropospheric and multipath errors.
Traps: confusing RNAV and RNP (RNP includes on-board monitoring and alerting); assuming RAIM is always available; forgetting that GNSS can be affected by interference and jamming. Another trap is confusing accuracy with integrity.
Rule of thumb: RNAV = can fly a path; RNP = can fly a path and knows when it cannot.