A pilot is cleared for an RNAV (GPS) approach to Runway 18. The approach chart depicts a Final Approach Fix (FAF) at 5.0 NM from the runway threshold. The published altitudes are 2,000 feet MSL at the FAF and a Minimum Descent Altitude (MDA) of 500 feet MSL. If the pilot is flying a Category B aircraft with a ground speed of 100 knots, what approximate descent rate is required to maintain a 3.0-degree glideslope from the FAF to the MDA?

Correct answer: D. 500 feet per minute.

First, calculate the total altitude to lose: FAF altitude (2,000 ft) - MDA (500 ft) = 1,500 feet. Next, calculate the distance over which this descent occurs. The FAF is 5.0 NM from the threshold. Assuming the MDA is reached at the Missed Approach Point (MAP) which is typically at the threshold for RNAV, the descent distance is 5.0 NM. The standard formula for descent rate on a 3-degree glideslope is Groundspeed x 5. So, 100 knots x 5 = 500 feet per minute. This descent rate will bring the aircraft to the MDA at the MAP, which is approximately 5NM. If the MDA is reached prior to the MAP, the pilot must level off at the MDA until the MAP.