Instrument Rating Checkride Practice Test

What is the formula to calculate a 3° glideslope?

1. Ground speed/2 = FPM

2. Airspeed/2 = FPM

3. Altitude/2 = FPM

4. Calculated descent rate/2 = FPM

The correct answer is: Airspeed/2 = FPM

The formula to calculate a 3° glideslope involves using airspeed to determine the feet per minute (FPM) descent rate required to maintain that glideslope during an approach. The critical aspect of this context is understanding that a 3° descent path refers to a typical angle used in instrument approaches, particularly because it correlates with a standard rate of descent based on airspeed. When utilizing airspeed to find the descent rate, the formula is Airspeed/2 = FPM for a 3° glideslope. This means that if you're flying at an indicated airspeed of, say, 120 knots, you would divide that by 2, yielding a descent rate of 600 feet per minute. This descent rate helps pilots maintain the glide path needed for a safe and stabilized approach to landing. The other options, while they might suggest calculating descent rates, do not accurately describe the relationship with maintaining a 3° glideslope in the context of normal approaches. The crucial element is using airspeed as the reference, which specifically leads to the correct calculation for descent rate in this scenario.