The Vertical Descent Point (VDP) on a non-precision approach offers pilots a calculated reference point where a normal descent angle can be commenced from the Minimum Descent Altitude (MDA) to the runway. Determining this point involves a trigonometric calculation related to the altitude difference and the descent angle. A common method uses a ratio derived from the descent angle. For example, a 3-degree descent angle, a standard for many instrument approaches, corresponds to a ratio of approximately 300 feet of altitude loss per nautical mile. One could divide the height above touchdown (HAT) by this ratio (approximately 300) to determine the distance in nautical miles back from the runway threshold that the VDP is located. This distance is then annotated on the approach chart or calculated using cockpit avionics.
Establishing the VDP provides a stabilized descent path, enhancing safety and reducing the risk of controlled flight into terrain (CFIT). Utilizing a VDP encourages a consistent approach profile, lessening the likelihood of abrupt maneuvers near the ground. Furthermore, it supports improved pilot workload management by providing a clear decision point for descent. Originally, these calculations were performed manually. However, modern flight management systems (FMS) and GPS-based avionics often automate the calculation and display of the VDP, increasing precision and ease of use.
