Plain English Meaning

These are short codes a pilot writes on the flight plan to tell air traffic control that the aircraft can fly RNAV 2 routes, and which kinds of navigation equipment it will use to do so. C1 means it can use any approved equipment, C2 means satellite navigation, C3 means ground-based distance signals, and C4 means distance signals combined with onboard inertial navigation.

Full Definition

PBN/C1-C4 are ICAO flight plan descriptors used in Item 18 of the flight plan to indicate that an aircraft is approved for RNAV 2 operations using specific navigation sensors. C1 indicates RNAV 2 capability using all permitted sensors (GNSS, DME/DME, DME/DME/IRU). C2 indicates RNAV 2 using GNSS. C3 indicates RNAV 2 using DME/DME. C4 indicates RNAV 2 using DME/DME/IRU. The codes are appended after the PBN/ prefix in Item 18 of the ICAO flight plan to declare which RNAV 2 navigation methods the aircraft is to use.