Question

When does an ILS localizer coupling loop become unstable?

(a) Aircraft range is infinity

(b) Aircraft range is close to zero

(c) When too many aircraft are present

(d) When no aircraft is present

I got this question during an online interview.

I want to ask this question from ILS/MLS Coupled Landing System and Automatic Landing in division Autopilots and Flight Management Systems of Avionics

Answer 1

Correct option is (b) Aircraft range is close to zero

For explanation I would say: In the localizer coupling loop gain increases as range between aircraft and runway decreases. The gain reaches a point where it becomes too large and the loop becomes unstable. Thus gain scheduling with range is required.