VDP Calculator (Visual Descent Point)
Find where to leave the MDA on a non-precision approach, when you get there and the altitude to be at each mile on a continuous descent.
TDZE from the chart, or the threshold elevation.
The angle is worked out from here down to the threshold crossing height.
Use the VDA or glide path angle printed on the chart (often 3.00°). No angle on the chart? 3° is the usual choice.
Height the path crosses the runway end. Charted, or about 50 ft. Enter 0 to aim at the threshold.
Gives the derived decision altitude (DDA). Often 50 ft where the operator allows it; 0 for none.
The reading at the runway end (DME beyond or at the runway).
0 when the MAP is at the threshold.
Distance from the threshold. Shows the angle and rate needed if you start down late.
How your VDP is worked out
Find your height above the runway, the slope of the path, then how far out the two meet.
- 1
Height above runway
900 − 400 ft
= 500 ft HAT - 2
Slope of the path
tan 3.0° × 6,076
= 318 ft per nm - 3
Distance out
(500 − 50) ÷ 318
= 1.41 nm VDP - 4
Timing to the runway
1.41 nm at 120 kt
= 42 s
Read more: the formula, a worked example, CDFA and the rules of thumb
A visual descent point (VDP) is the point on a straight-in non-precision approach where a normal descent from the MDA to the touchdown zone can start, if you have the runway environment in sight. Leave the MDA before it and you may be low over obstacles; leave it well after and you face a steep, unstable dive to the runway. The FAA AIM (paragraph 5-4-5) describes the VDP and the "V" that marks it on the chart profile. When no VDP is charted, this calculator works one out from the MDA, the touchdown zone elevation and the path angle. For the vertical speed on any glide path use the descent rate calculator, and to plan the start of the descent from cruise use the top of descent calculator.
The formula
HAT (height above touchdown) = MDA − touchdown zone elevation
slope (ft per nm) = tan(angle) × 6,076 (3° ≈ 318 ft per nm)
VDP distance from threshold (nm) = (HAT − TCH) ÷ slope
DME at the VDP = DME at the threshold + VDP distance
time FAF → VDP = (FAF distance − VDP distance) ÷ ground speed
vertical speed = slope × ground speed ÷ 60
derived DA = MDA + add-on
altitude on the path at distance d = TDZE + TCH + d × slope
angle from the FAF = arctan((FAF altitude − TDZE − TCH) ÷ (FAF distance × 6,076))
Rules of thumb: VDP ≈ HAT ÷ 300 nm for a 3° path, and VDP ≈ HAT ÷ 10 seconds before the threshold at typical approach speeds.
Worked example
The MDA is 900 ft and the touchdown zone is 400 ft, so the HAT is 900 − 400 = 500 ft. On a 3° path, tan 3° = 0.05241, so the slope is 0.05241 × 6,076 = 318.4 ft per nm. With a 50 ft threshold crossing height the VDP is (500 − 50) ÷ 318.4 = 1.41 nm from the threshold. The HAT ÷ 300 rule gives 500 ÷ 300 = 1.67 nm.
At 120 kt the vertical speed is 318.4 × 120 ÷ 60 = 637 ft/min, and the VDP is 1.41 ÷ 120 × 3,600 = 42 seconds from the threshold (the HAT ÷ 10 rule says 50 seconds). With the FAF 5 nm out, the VDP is 5 − 1.41 = 3.59 nm past it: 3.59 ÷ 120 × 3,600 = 1 min 48 s after the FAF. The full 5 nm from the FAF to a MAP at the threshold takes 2 min 30 s.
With a 50 ft add-on the derived DA is 900 + 50 = 950 ft. The path reaches it (950 − 400 − 50) ÷ 318.4 = 1.57 nm from the threshold. On the CDFA table the path is at 400 + 50 + 5 × 318.4 = 2,042 ft over the FAF (2,040 rounded), then 1,720 ft at 4 nm, 1,410 ft at 3 nm and 1,090 ft at 2 nm; 1 nm (770 ft) is below the MDA, so you only go there with the runway in sight.
CDFA: flying the approach without level-offs
A continuous descent final approach (CDFA) flies the final segment of a non-precision approach as one steady descent from the FAF, like an ILS, instead of "dive and drive" steps. ICAO Doc 8168 (PANS-OPS) recommends it, and EASA Air OPS make it the standard technique for commercial operators. Check your altitude against the table at each DME fix: above the figure means you are high, below means low. Most charts show these check altitudes rounded to the nearest 10 ft; rounding up keeps you on or just above the path.
Because you go around at the derived DA without levelling off, the aircraft sinks a little before it climbs. That is why many operators add a margin to the MDA (often 50 ft, see FAA AC 120-108 and EASA AMC1 CAT.OP.MPA.110). If yours does not allow an add-on, set it to 0.
Where the rules come from
- FAA AIM 5-4-5: what a VDP is, the "V" on the profile, and that you should not descend below the MDA before reaching the VDP.
- FAA Order 8260.3 (US TERPS): how the VDP is placed, from the visual descent angle and threshold crossing height up to the MDA.
- ICAO Doc 8168 (PANS-OPS) Vol I: the CDFA technique and the descent profile tables printed on charts.
- FAA AC 120-108 and EASA AMC1 CAT.OP.MPA.110: CDFA and an add-on to the MDA for a derived decision altitude.
- Flight Safety Foundation ALAR Briefing Note 7.1: stabilised approach guidance, including a sink rate of about 1,000 ft/min.
Things to watch
- DME is slant range. At 1 nm and 1,000 ft above the station the reading is about 0.01 nm high; it only matters very close to the DME.
- Cold weather makes your true altitude lower than the altimeter shows. Apply your cold temperature corrections to the MDA and check altitudes.
- A charted VDP always wins. If the chart shows a VDP or a descent table, use those figures. Some approaches have no VDP because of obstacles in the visual segment.
- Units: 1 nm = 1,852 m = 6,076 ft; 1 kt = 101.27 ft/min; 1 m/s = 196.85 ft/min.
Planning and training aid only. Always use your approved flight manual, operator procedures and official charts.
Common questions
How do you calculate a visual descent point?
Take the MDA height above the touchdown zone (HAT), take away the threshold crossing height, and divide by the slope of the path in feet per nautical mile. With an MDA 500 ft above the runway, a 50 ft crossing height and a 3° path of 318 ft per nm, the VDP is 450 ÷ 318.4 = 1.41 nm from the threshold.
What is the HAT ÷ 300 rule for a VDP?
It is a quick way to find the VDP for a 3° path: divide the height above the touchdown zone by 300 to get the distance in nautical miles. For a HAT of 500 ft that gives 1.67 nm. It ignores the threshold crossing height and rounds the slope down from 318 ft per nm, so it puts the VDP a little further out than the exact figure.
How do I find the VDP using DME?
Work out the VDP distance from the threshold, then add the DME reading at the threshold. If the DME reads 0.6 at the runway end and the VDP is 1.41 nm out, start down at about 2.0 DME. DME measures slant range, so very close to the station the reading is a little more than the distance over the ground.
How long after the FAF do I reach the VDP?
Subtract the VDP distance from the FAF distance and divide by your ground speed. With the FAF 5 nm from the threshold and the VDP at 1.41 nm, you fly 3.59 nm. At 120 kt that takes 1 minute 48 seconds. The timing table shows the same figures for 70 to 160 kt.
What is a derived decision altitude for a CDFA?
When a non-precision approach is flown as a continuous descent, many operators add a margin to the MDA, often 50 ft, and treat it as a decision altitude. The go-around starts there, so the height lost while the aircraft changes to a climb does not take it below the MDA. Use the figure your operator has approved.
What happens if the VDP is past the missed approach point?
Then you reach the missed approach point before the VDP. You must have the required visual references at the MAP to continue, or go around. The calculator warns you when the VDP you have worked out lies beyond the MAP.
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