AIM ¶ 4-7-4 — Single LRNS Authority
AIM 4-7-4 explains how operators can use 50 NM lateral separation in Gulf of America CTAs with a single long-range navigation system via OpSpec/MSpec/LOA B054.
AIM 4-7-4 explains that operators flying in the Gulf of America Control Areas (CTAs) can be authorized to use 50 NM lateral separation even when equipped with only a single long-range navigation system (LRNS) — they don't necessarily need dual systems.
This authorization is granted under RNP 10 (Required Navigation Performance) and is issued through one of the following operator-specific approvals:
- OpSpec (Operations Specification)
- MSpec (Management Specification)
- LOA B054 (Letter of Authorization B054)
Why it matters: Operating in oceanic/remote airspace normally requires redundant long-range navigation equipment. This authorization provides flexibility for operators whose aircraft don't carry dual LRNS, while still meeting the navigation accuracy standard required for reduced lateral separation.
To pursue this authorization, operators contact their FSDO (Flight Standards District Office) or CMO (Certificate Management Office). FAA aviation safety inspectors use the qualification criteria in FAA Order 8900.1, Volume 3, Chapter 18, Section 4 to evaluate and issue B054. Note that this AIM paragraph is informational; the actual authority comes from the operator's issued OpSpec, MSpec, or LOA.