What does RNAV1 mean on the approach chart, and what percentage of time must the system error remain bounded?

• A. RNAV1 means GPS-based navigation with total system error bounded by +1 NM for 95% of the total flight time.
• B. RNAV1 indicates vertical guidance with a bound of +/- 0.5 NM for 90% of the time.
• C. RNAV1 indicates any RNAV approach with a bound of +/- 2 NM for 95%.
• D. RNAV1 requires manual navigation with no error bound.

Answer: (A)

RNAV1 is a lateral navigation performance standard for RNAV approaches using GPS. It means the navigation system must keep the total system error within 1 nautical mile for 95% of the total flight time. In practice, most of the approach is flown with lateral guidance that stays within 1 NM of the intended path, and only a small portion of time (about 5%) may see larger deviations. This standard focuses on horizontal accuracy and consistency, not vertical guidance—the latter would be provided by different RNAV categories like LPV or LNAV/VNAV. The other statements either imply vertical guidance, a different error bound, a different time percentage, or manual navigation, which aren’t what RNAV1 specifies.