|CHAPTER 3. Navigation
Flying the Descent
The key to flying a descent is to know your position relative to the pathway-in-the-sky at all times. If you drift off the path, you need to modify the descent speed and/or descent rate in order to rejoin the descent path. Many FMSs do not give a direct indication of progress during a descent. You must be very familiar with the indirect indications of the VNAV descent. In this case, follow the planned descent rate and speed as closely as possible and be mindful of altitude and position while approaching the crossing restriction fix.
Determining Arrival at the Top-of-Descent Point
All navigation systems provide some type of alert informing the pilot of arrival at the planned top of descent point, and that it is time to begin the descent at the speed and rate entered into the FMS.
If air traffic control is able to accommodate your request, the ideal point to begin the descent is at the planned top-ofdescent point. If air traffic control is unable to accommodate such a request, one of two scenarios will ensue: an early descent or a late descent.
Beginning descent before reaching the planned top-ofdescent point means you must set aside descent planning and proceed without the benefit of vertical guidance offered by the navigation system. If, during the descent, the navigation computer does not display position with respect to the planned descent path, you must simply do the best possible to arrive at the crossing restriction at the assigned altitude. If the navigation system does display position with respect to the planned descent path, you can usually recapture the planned descent path and resume flying with vertical guidance from the computer. The basic technique is to initiate descent at a reasonable descent rate that is less than the planned descent rate. If you follow this initial descent rate, you will eventually intercept the planned descent path, as shown in Figure 3-35.
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