This paper discusses the amplitude-polarization method of aircraft pitch angle detection using horizontally polarized radio beacon signals. The aircraft pitch angle estimation is done using the ratio of the in-phase orthogonal horizontal linearly polarized amplitudes of the radio beacon signals received within the linearly polarized basis. It was found that the measured value of the pitch angle coincides with its true value only at a certain angle of orientation of the unit vectors of the polarization basis to the longitudinal axis of the aircraft. When this angle deviates from the set value, errors occur in measuring the pitch angle equal to the absolute deviation of the unit vectors' orientation.