________ shall not be used as the sole source of navigation on an instrument approach.

• A. GPS coordinates from the database
• B. Aircrew-defined FMC waypoints
• C. VOR/DME fixes
• D. Inertial nav system only

Answer: (B)

When flying an instrument approach, your navigation must be anchored to a verified, published reference rather than points created purely by the crew. Aircrew-defined FMC waypoints are generated inside the flight management computer to shape a route, but they don’t carry the same independent validation as published fixes or database-provided navaids. If you relied on those crew-created points as the sole navigation source, any database error, mis-entry, or mismatch with the actual approach could go unnoticed and jeopardize obstacle clearance and the integrity of the approach.

That’s why this is the best choice: you can use GPS coordinates from the navigation database or conventional VOR/DME fixes as you navigate an instrument approach, because they provide validated, real-world references. Relying only on an inertial navigation system isn’t acceptable for the approach either, since INS drifts over time and lacks independent verification without another updating source.