An aircraft propeller, the propeller rotatable about an axis and comprising a plurality of blades each rotatable through a plurality of blade angles, the propeller having at least a first mode of operation where the plurality of blades are operated at a positive blade angle and a second mode of operation where the plurality of blades are operated at a negative blade angle, and a blade angle position feedback system, the blade angle position feedback system comprising: an annular member operatively connected to rotate with the propeller, the annular member comprising at least two circumferentially-spaced first singularities (102 A, 102 C) extending substantially parallel to the axis and at least one second singularity (102 B) extending non-parallel to the first singularities (102 A, 102 C), wherein the singularities (102 A, 102 B, 102 C) are on an outer face of the annular member, and the at least one sensor is mounted adjacent the outer face; at least one sensor fixedly mounted adjacent the annular member, the at least one sensor configured for successively detecting a passage of each one of the at least two first singularities (102 A, 102 C) and the at least one second singularity (102 B as the annular member is rotated and axially displaced and for generating a sensor signal accordingly, the annular member and at least one sensor configured for relative axial displacement between a first relative axial position and a second relative axial position, the first position corresponding to the first mode of operation and the second position corresponding to the second mode of operation; and a detection unit connected to the at least one sensor for receiving the sensor signal therefrom, determining on the basis of the sensor signal a time interval elapsed between the passage of successive ones of the at least two first singularities (102 A, 102 C) and the at least one second singularity (102 B), and computing from the time interval a blade angle position for the plurality of blades. an annular member operatively connected to rotate with the propeller, the annular member comprising at least two circumferentially-spaced first singularities (102 A, 102 C) extending substantially parallel to the axis and at least one second singularity (102 B) extending non-parallel to the first singularities (102 A, 102 C), wherein the singularities (102 A, 102 B, 102 C) are on an outer face of the annular member, and the at least one sensor is mounted adjacent the outer face; at least one sensor fixedly mounted adjacent the annular member, the at least one sensor configured for successively detecting a passage of each one of the at least two first singularities (102 A, 102 C) and the at least one second singularity (102 B as the annular member is rotated and axially displaced and for generating a sensor signal accordingly, the annular member and at least one sensor configured for relative axial displacement between a first relative axial position and a second relative axial position, the first position corresponding to the first mode of operation and the second position corresponding to the second mode of operation; and a detection unit connected to the at least one sensor for receiving the sensor signal therefrom, determining on the basis of the sensor signal a time interval elapsed between the passage of successive ones of the at least two first singularities (102 A, 102 C) and the at least one second singularity (102 B), and computing from the time interval a blade angle position for the plurality of blades.