LOC Convergence Function – (when transiting from NAV to LOC mode)

This function ensures that there is a minimum intercept angle of 20 degrees maintained when transitioning from Navigation (NAV) mode to Localizer (LOC) mode so that there is no endless delay in capture. It determines the roll-in and roll-out rates of the aircraft from the bank during the intercept. When interception HDG is selected, this delay is left to pilot’s discretion. Sometimes, the aircraft may experience a jerky “S” turn during LOC interception due to this function.

Aircraft is guided with a converging track of 20 deg from the LOC axis, when all the following conditions are met:

• NAV mode is engaged and LOC mode is armed
• The aircraft is withing 20 NM of destination runway
• The difference between the aircraft track and the QFU (magnetic bearing of landing runway) is less than 20 degree.

Enhanced LOC capture function

The Enhanced LOC Capture function significantly improves the effectiveness of Localizer (LOC) capture. It ensures precise alignment with the LOC beam while minimizing the risk of overshooting. Leveraging the accuracy of GPS PRIMARY when available, FMS utilizes the aircraft’s precise position data to calculate the optimal distance for initiating a heading change and engaging LOC* mode.

This calculated region, known as the pre-capture zone.

Conditions for LOC Capture in pre-capture zone:

• LOC deviation is more than 2.3 dots
• FMS GPS PRIMARY
• Difference between track and QFU is between 25 deg and 115 deg
• Guidance roll order is such that LOC* will capture OC beam without overshoot
• Interception on 90 deg and even 115 deg approach angle to the beam is possible

When LOC deviation becomes lower than 2.3 dots, LOC* mode use actual LOC beam deviation. Flight crew will observe movement of LOC deviation only when LOC deviation is less than 2 dots.