In this paper, we propose a solution separation monitor to detect Global Navigation Satellite System (GNSS) spoofing using Inertial Navigation Systems (INS), which compares the position solution of a tightly coupled INS/GNSS to an INS-only position solution. In our prior work –, we introduced an innovation sequence monitor that provided high integrity detection against slowly growing faults, but it lacked fault exclusion capability and assumed coincident monitor start at fault onset. In this work, we also prove that the solution separation monitor provides better detection capability compared to the innovation sequence monitor. The solution separation monitor enables direct fault exclusion after spoofing detection since the INS-only position solution is not corrupted by re-calibration using spoofed GNSS signals. We also address the monitor start and run time issue by proposing a sequential window monitoring method for which it is possible to explicitly quantify protection level for a given time frame of monitoring. For slowly growing faults which might remain undetected by the solution separation monitor we analyze the spoofer’s tracking error as an aid to detection. Wind gusts cause rapid movement of aircraft which cannot be tracked in real time and hence can potentially help with detection. We model spoofer’s tracking error based on empirical vertical velocity variation data of civil aircraft due to wind gusts. The solution separation monitor performance is shown to be enhanced with the presence of spoofer’s tracking error even when the spoofer does not inject any fault profiles.