At some point in your flying career, either in an FAA Practical Test or in real life, you will be required to perform a visual approach to a landing. In a simulator checkride, typically the electronic glideslope and VASI (visual approach slope indicator) will be rendered inoperative.
For planning purposes, we will use 3 degrees as the desired approach path. That is a typical ILS glideslope and typical VASI glideslope. For a 3-degree descent, your descent rate (vertical speed) will need to be 1/2 your groundspeed times 10. For example, if your groundspeed is 100 knots, you will need to descend at 500 feet per minute to remain on a 3-degree glideslope.
You can read your groundspeed directly from your glass-cockpit instruments. What if you're flying an aircraft with antique gauges? That's where some mental math comes in. Your groundspeed is your true airspeed minus the headwind. You can estimate the headwind by using ATIS winds and adding a few knots for the increased winds (assumed) at approach altitude. How about your true airspeed? Calculate your true airspeed by increasing your indicated airspeed by 2 percent for every 1000 feet above sea level. For example, if you are flying the approach at 90 knots at an average altitude of 5000 feet in Colorado, your true airspeed will be 10 percent higher than your indicated airspeed. So your true airspeed will be 100 knots (actually, 99 knots, but we're doing PILOT math!). If your headwind is 10 knots, your groundspeed is 90 knots, so you will descend at 450 feet per minute.
Here's an even easier way to maintain a 3-degree glideslope: simply fly towards the runway at the glideslope intercept altitude, maintaining final approach airspeed. When you fly over the outer marker (the blue marker beacon light, or the DME for the final approach fix), simply lower the nose 3 degrees and hold that pitch. Wherever the touchdown zone appears in your windscreen, hold that sight picture all the way down. Piece of cake!
