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How to determine your VDP

The following describes three techniques for estimatine a Non-precision approaches VDP when the VDP is not published. The first two techniques show two methods of estimating the distance (DME) from the VDP to the runway. The third technique describes how to estimate timing to the VDP from the FAF.

Estimating the distance from the VDP and the runway

Technique one - Take the height above touchdown (HAT) as published in an approach, round it to the nearest hundreds, multiply it times three, and divide by ten. For example, if the HAT is 785 feet, round it to 8 and multiply it times 3 and divide it by 10 to get 2.4 nautical miles. If the HAT were 600 feet, round it to 6, multiply it by 3 and divide it by 10 to get 1.8 miles. If the HAT were 1200 feet, round it to 12, multiply it by 3 and divide it by 10 to get 3.6 nautical miles.

Technique two - It takes one nautical mile to descend 300 feet on a 3 degree glide slope. Based on this fact, you can estimate the distance to descend. For example, if you had to descend 600 feet (HAT = 600), we know that it would take 1 nautical mile to descend 300 feet, therefore it must take 2 miles to descend 600 feet. If the HAT were 850 feet, it would take between 2 nautical miles (600 feet) and 3 nautical miles (900 feet) or since 850 is closed to 900, about 3 nautical miles.

Estimating the Timing from FAF to the VDP

Take the timing published from the FAF and Missed Approach Point (MAP) and subtract the HAT rounded to the nearest tenths. For example: if the missed approach timing was 2:45 and the HAT was 600; subtract 60 seconds (600 rounded to the nearest tenths) from 2:45 to get 1:45. In this case, timing for 1:45 would identify the VDP. If the runway was not in sight at the VDP, the pilot should continue to the MAP and execute a missed approach.