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Descending with a plan
Many pilots struggle with planning their descents from cruising altitude and arrivals after a cross-country flight. It doesn�t need to be a struggle. A little planning�and some basic math�can help.
When approaching your destination on a VFR cross-country flight, plan your descent to arrive at pattern altitude 3 to 5 miles from the field. This gives you ample time to locate the airport visually, scan for other traffic in the pattern right at the horizon, where it�s easiest to see, and plan your arrival.
Begin your descent with the knowledge that you need 4 miles for each thousand feet you have to lose with a groundspeed of 120 knots and a 500-foot-per-minute descent rate. If you�re flying at 8,500 feet, and the field elevation is 1,500, you have to lose 6,000 feet to get to pattern altitude. Six (thousand) times 4 miles equals 24 miles, so begin your VFR descent 27 miles from the field to arrive at pattern altitude when you�re 3 miles out.
To determine the proper rate of descent to remain on a 3-degree glideslope, multiply your groundspeed in knots by five; this will give you the proper descent rate in feet per minute. If you fly the glideslope at 90 knots, the correct descent rate will be 450 feet per minute.
A few moments spent planning your descent while still at cruising altitude will pay major dividends for you and your passengers� smooth, no-fuss arrivals at your destination. And the math necessary to make it happen shouldn�t require much thought.
Rusty Sachs is a Master Instructor and the director of the National Association of Flight Instructors.
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