A method of controlling a crossing threshold used in determining a rotational speed of a propeller of an aircraft engine, the method comprising: setting an initial value for the crossing threshold; receiving a sensor signal comprising a first series of pulses (135 A, 135 B, 135 C) indicative of passage of position markers about a circumference of a propeller shaft; generating a detection signal comprising a second series of pulses (155 A, 155 B, 155c) indicative of pulses within the first series of pulses (135 A, 135 B, 135 C) that have a zero-crossing transition (140 A, 140 B, 140 C) and a magnitude that exceeds the crossing threshold; determining the rotational speed of the propeller from the detection signal based on a time interval between a plurality of pulses of the second series of pulses (155 A, 155 B, 155 C); adjusting the crossing threshold as a function of the rotational speed of the propeller, comprising: comparing the rotational speed to a speed threshold (T RPM); when the rotational speed is less than or equal to the speed threshold (T RPM), maintaining the crossing threshold at the initial value; and when the rotational speed exceeds the speed threshold (T RPM), setting the crossing threshold at an adjusted value, the initial value having a different magnitude than the adjusted value; wherein setting the crossing threshold comprises a controller commanding a detection device to set the crossing threshold; wherein the detection device is configured to receive the sensor signal from a sensor and to generate the detection signal; wherein setting the crossing threshold at the initial value comprises the controller commanding the detection device to operate in a first mode and commanding the detection device to set the crossing threshold at a constant value or at a first ratio of a peak amplitude value of the sensor signal; and wherein setting the crossing threshold at the adjusted value comprises the controller commanding the detection device to operate in a second mode where the crossing threshold is set at a second ratio of a peak amplitude value of the sensor signal, the second ratio being different from the first ratio. setting an initial value for the crossing threshold; receiving a sensor signal comprising a first series of pulses (135 A, 135 B, 135 C) indicative of passage of position markers about a circumference of a propeller shaft; generating a detection signal comprising a second series of pulses (155 A, 155 B, 155c) indicative of pulses within the first series of pulses (135 A, 135 B, 135 C) that have a zero-crossing transition (140 A, 140 B, 140 C) and a magnitude that exceeds the crossing threshold; determining the rotational speed of the propeller from the detection signal based on a time interval between a plurality of pulses of the second series of pulses (155 A, 155 B, 155 C); adjusting the crossing threshold as a function of the rotational speed of the propeller, comprising: comparing the rotational speed to a speed threshold (T RPM); when the rotational speed is less than or equal to the speed threshold (T RPM), maintaining the crossing threshold at the initial value; and when the rotational speed exceeds the speed threshold (T RPM), setting the crossing threshold at an adjusted value, the initial value having a different magnitude than the adjusted value; comparing the rotational speed to a speed threshold (T RPM); when the rotational speed is less than or equal to the speed threshold (T RPM), maintaining the crossing threshold at the initial value; and when the rotational speed exceeds the speed threshold (T RPM), setting the crossing threshold at an adjusted value, the initial value having a different magnitude than the adjusted value; wherein setting the crossing threshold comprises a controller commanding a detection device to set the crossing threshold; wherein the detection device is configured to receive the sensor signal from a sensor and to generate the detection signal; wherein setting the crossing threshold at the initial value comprises the controller commanding the detection device to operate in a first mode and commanding the detection device to set the crossing threshold at a constant value or at a first ratio of a peak amplitude value of the sensor signal; and wherein setting the crossing threshold at the adjusted value comprises the controller commanding the detection device to operate in a second mode where the crossing threshold is set at a second ratio of a peak amplitude value of the sensor signal, the second ratio being different from the first ratio.