Most GPS-denied drones bluff. Ours hit a pitch-black tunnel, lost every visual feature, and turned itself around rather than fake a position. In contested airspace the failure that kills a drone isn't drift. It's a confident-but-wrong position: the estimator locks onto an empty scene, reports a clean-looking fix, and flies it into a wall. An honest "I don't know" is safer than a confident wrong answer. So we built the part that says "I don't know." A navigation integrity monitor sits outside the estimator and watches three things: how many usable landmarks it can see, how uncertain the position has grown, and whether the measurements still add up. When the tunnel went dark and features fell to near zero, it flipped RED, called the position untrustworthy, and triggered return-to-home at 52.5 seconds. It refused to guess. The point is that separation. Trust can't be judged by the same math that produced the position, any more than a witness can certify their own testimony. This is one seeded synthetic mission, not a flight test, but that structure holds no matter how good the navigation underneath gets. When your autonomy stack loses its landmarks, does anything tell it to stop trusting itself, or does it keep flying on the last confident guess? #GPSdenied #DroneAutonomy #BlueUAS #VIO