A system is provided for detecting a low-power error condition in a local area augmentation system (LAAS). The system receives a radio signal from a global positioning system (GPS) satellite and measures the wide band and narrow band power of the radio signal in real time. The system estimates the signal-to-noise ratio of the signal in real time based on average wide band and narrow band power measurements. A low signal-to-noise ratio indicates a low power condition. The system then calculates an error contribution due to the low power condition and sums the error contribution with other error contributions to determine the total error in a navigational measurement. To ensure error overbounding, the system may subtract a confidence offset from the signal-to-noise ratio to obtain a lower confidence limit.