Due to the ever-growing threat of GPS spoofing, it has become necessary for the aviation sector to develop an effective means of detection. This article focuses on two complementary spoofing-detection techniques that are available on commercial GPS receivers and thus require no additional hardware to operate. The primary methodology for detection is using a combination of radio power monitoring metrics, levering both automatic gain control and C/N0 measurements, along with multiple correlations for signal distortion to provide a best practices spoofing-detection algorithm, which is able to distinguish between interference and spoofing. The article first assesses nominal statistics for both metrics compiled from more than 250 h of nominal data collected from multiple wide area augmentation system stations. These data are compared to previous collections to validate the thresholds and false alarms rates and establish a complete testing methodology. These tests and thresholds are then assessed with the Texas spoofing test battery series of GPS spoofing data sets to confirm detection capabilities. Finally, these tests and thresholds are applied to assess the GPS signal of six extended flights over the United States to assess the performance on an aircraft.