Wind Top-of-descent point Bottom-of-descent point ECA VOR Cruising altitude ft 0 0 0 1 1 Assigned altitude ft 0 0 0 3 To Cruising speed knots 0 7 2 Descent speed and rate eed and rate knots @ 1,000 fpm 0 8 1 Elements of Descent Planning Calculations Coordinating Calculations with Aeronautical  Charts Manual Descent Calculations Alternate Navigation Planning Figure 3-27. The descent planning task. to start the approach. In either case, descending from a  cruising altitude to a given waypoint and altitude requires  both planning and precise flying. and a descent rate of 1,000 feet per minute (fpm). Assuming a  10‑knot headwind component, groundspeed in the descent is  180 knots. Referring to the table in  Figure 3-28,  the planned  descent speed and rate indicate a ratio of 3.0. This means that  you will need 3 NM for every 1,000 feet of descent. You  must descend a total of 8,000 feet (11,000 feet – 3,000 feet).  A total of 24 NM is needed to descend 8,000 feet (3 NM ×  8 = 24 NM), and must, therefore, begin the descent 24 NM  away from the end‑of‑descent point. Figure 3-27  illustrates the basic descent planning task. The  task begins with an aircraft flying at an assigned cruising  altitude. The aircraft must descend to an assigned altitude  and reach that assigned altitude at a designated bottom‑of‑ descent point. The next step is to choose a descent rate and  a descent speed. The ultimate goal is to calculate a top‑of‑ descent point, which is the point at which, if you begin the  descent and maintain the planned descent rate and airspeed,  you will reach the assigned altitude at the designated bottom‑ of‑descent point. Another technique for calculating descents is to use the  formula shown in  Figure 3-29.  A descent table can be found  in the front of each set of U.S. Terminal Procedures on  page D‑1. Working through the formula for the ECA VOR  crossing restriction example, 8 minutes is needed to descend  8,000 feet at the planned descent rate of 1,000 fpm. At your  planned descent speed of 180 knots, you will cover 3 NM  per minute. Thus, in 8 minutes, you will cover 24 NM. Once  again, you must start the descent 24 NM prior to ECA to meet  the crossing restriction. In a basic aircraft, you must rely on manual calculations to  perform the descent planning task. In an advanced avionics  aircraft, there are two descent planning methods available:  (1) manual calculations, and (2) the vertical navigation  features of the FMS unit. Skillful pilots use both methods  and cross‑check them against one another in order to reduce  the possibility of error and help keep the pilot “in the loop.” Regardless of which method is used, it is always a good idea  to locate the top‑of‑descent point chosen on the aeronautical  chart.  Figure 3-30 shows a chart that covers the area  surrounding the ECA VOR. A top‑of‑descent point 24 NM  prior to ECA is located 3 NM before PATYY intersection. The simplest technique for calculating the distance required  to descend uses a descent ratio. The table in  Figure 3-28  lists a descent ratio for many combinations of planned descent  speeds and descent rates. Calculating a descent is a simple  matter of looking up the descent ratio for your target descent  rate and groundspeed, and multiplying the descent ratio by  the number of thousands of feet in altitude that you must  descend. For example, suppose you are asked to descend from  11,000 feet to meet a crossing restriction at 3,000 feet. Since  there is a 200‑knot speed restriction while approaching the  destination airport, you choose a descent speed of 190 knots  Using the aeronautical chart to locate the top‑of‑descent point  has a second advantage. Since regulations require you to have  an alternate means of navigation onboard if the computer  does not comply with TSO 146B, the aeronautical chart  allows you to check minimum altitudes for VOR reception  3-20