Instrument Rating Checkride Practice Test

What is the primary function of marker beacons in the ILS system?

1. To guide the aircraft on the runway

2. To indicate the aircraft position during approach

3. To provide weather information

4. To assist in navigation outside controlled airspace

The correct answer is: To indicate the aircraft position during approach

Marker beacons play a crucial role in the Instrument Landing System (ILS) by providing visual and auditory signals to pilots as they approach the runway. Their primary function is to indicate the aircraft's position during the approach phase of a flight. Each marker beacon corresponds to specific points along the approach path, such as the outer marker, middle marker, and inner marker, which help pilots determine their distance from the runway and ensure they are on the correct glide slope. For instance, the outer marker typically indicates that the aircraft is approximately 4 to 7 miles from the runway threshold and serves as a point for the pilot to prepare for landing procedures. The middle marker marks a position closer to the runway, usually at about 3,500 feet from the threshold, and alerts the pilot that they are nearing the decision height. The inner marker, when present, denotes the point just before the landing occurs. While guiding aircraft on the runway and providing weather information are important, those functions are served by different systems such as runway lights and automatic weather observation systems. Similarly, navigation outside controlled airspace typically involves other types of navigational aids, not specifically the function of marker beacons within the ILS framework. Hence, the indication of aircraft position during approach is the