AIM Text
- In order for an operator with RNP 10 or RNP 4 authorization to obtain 50 NM lateral separation in the Gulf of America CTAs/FIRs, and therefore obtain preferred routing available to RNP authorized aircraft, the international flight plan form (FAA 7233-4) must be annotated as follows:
- Item 10a (Equipment) must include the letter “R.”
- Item 18 must include either “PBN/A1” for RNP 10 authorization or “PBN/L1” for RNP 4 authorization.
- Indication of RNP 4 authorization implies the aircraft and pilots are also authorized RNP 10.
- Chapter 5, Section 1, of this manual includes information on all flight plan codes. RNP 10 has the same meaning and application as RNAV 10. They share the same code.
Source: FAA Aeronautical Information Manual · current edition · paragraph 4-7-5.
Research Notes
AIM 4-7-5 covers Direction Finding Service (DF) — a legacy radio-direction-finding service that is largely historical now but may still be available at some FSS locations.
How DF service worked: A lost pilot would call FSS on 121.5 or VHF. The FSS facility would take a directional bearing on the transmission. Combined with bearings from multiple stations, the FSS could triangulate position and provide guidance.
Modern relevance: Largely superseded by GPS, ADS-B, and radar coverage. A lost pilot today can request "radar position" from ATC instead. DF service remains available at some FSS locations as a backup.
Reference: AIM 4-7-5.