FAA Instrument Rating Written Practice Test

To maintain the electronic glide slope while flying at 120 knots indicated airspeed (KIAS) with a headwind, it is important to consider how the headwind affects the aircraft's descent rate. The standard rate of descent for a glide slope is typically around 700 feet per minute, assuming a configuration that supports an airspeed of approximately 120 knots in calm conditions.

However, flying into a headwind of 15 knots reduces the relative ground speed, meaning the aircraft effectively travels slower across the ground compared to its indicated airspeed. This requires an adjustment in the rate of descent. To maintain the glide slope, a lower descent rate is often needed, as the increased headwind reduces the ground speed that affects glide slope interception.

After accounting for the headwind, the correct calculation shows that the adjusted rate of descent to maintain the glide slope at a 120 KIAS with a 15-knot headwind is approximately 555 feet per minute. This lower rate of descent allows the aircraft to follow the glide path accurately, leading to a stable approach and landing.

In this case, the selected answer reflects a calculated adjustment for maintaining the correct glide path based on the conditions presented.