descent rate. This information must be updated while  in flight for changes in altitude, weather, and wind. The  approach gate is an imaginary point used by ATC to vector  aircraft to the final approach course. The approach gate  is established along the final approach course 1 NM from  the final approach fix (FAF) on the side away from the  airport and is located no closer than 5 NM from the landing  threshold. Flight manuals or operating handbooks may also  contain a fuel, time, and distance to descend chart that  contains the same information.  One technique that is often used is the descent rule of  thumb, which is used to determine when you need to  descend in terms of the number of miles prior to the point  at which you desire to arrive at your new altitude. First,  divide the altitude needed to be lost by 300. For example,  if cruising altitude is 7,000 feet and you want to get down  to a pattern altitude of 1,000 feet. The altitude you want to  lose is 6,000 feet, which when divided by 300 results in 20.  Therefore, you need to start your descent 20 NM out and  leave some extra room so that you are at pattern altitude  prior to the proper entry. It is also necessary to know what  rate-of-descent (ROD) to use.  To determine ROD for a three-degree path, simply multiply  your groundspeed by 5. If you are going 120 knots, your  ROD to fly the desired path would be 600 fpm (120 × 5  = 600). It was determined in the previous example that a  descent should be initiated at 20 NM to lose 6,000 feet. If  the groundspeed is 120 knots, that means the aircraft is  moving along at 2 NM per minute. So to go 20 NM, it takes  10 minutes. Ten minutes at 600 fpm means you will lose  6,000 feet.  The calculations should be made before the flight and rules  of thumb updates should be applied in flight. For example,  from the charted STAR pilots might plan a descent based on  an expected clearance to “cross 40 DME West of Brown VOR  at 6,000” and then apply rules of thumb for slowing down  from 250 knots. These might include planning airspeed at 25  NM from the runway threshold to be 250 knots, 200 knots at  20 NM, and 150 knots at 15 NM until gear and flap speeds  are reached, never to fall below approach speed.  Vertical navigation (VNAV) is the vertical component of  the flight plan. This approach path is computed from the  top-of- descent (TOD) point down to the end-of-descent  waypoint (E/D), which is generally the runway or missed  approach point, which is slightly different than to the  approach gate for non-flight management system (FMS)  equipped aircraft. [Figure 3-2] The VNAV path is computed  based upon the aircraft performance, approach constraints,  weather data (winds, temperature, icing conditions, etc.)  and aircraft weight.  Vertical Navigation (VNAV) Planning  Figure 3-2. VNAV path construction.  3-4 