Visual Descent Point Challenge
An enhanced VDP exercise using the existing descent math: place a VDP and observe the resulting profile.
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On a straight-in non-precision approach you level at the MDA and look for the runway. The visual descent point (the green V) is where a normal descent from the MDA to the runway begins; leave the MDA before it and you are low over the approach area, after it and you need a steep, fast descent — or a go-around. Drag your own cyan V along the MDA and watch the amber descent: the angle to the threshold, the PAPI lights in the corner and the descent rate tell you how it would feel.
Without a published VDP you can work one out. The quick rule is the height above touchdown divided by 300 (about a 3° path, in NM); the IFR Trainer’s Descent module gives the exact distance for any angle to the touchdown point; and a charted VDP is placed on the PAPI (or VDA) angle through the threshold crossing height, so it is a little closer in. Then find it by DME or by the time from the FAF at your groundspeed.
Press Challenge: you fly level at the MDA toward the runway — with or without a published VDP — and press Descend now where you choose. The descent is graded on its angle against the PAPI. Five items per round, all different.
Assumption: schematic profile — never a real procedure, never for navigation. The touchdown zone elevation is taken as the threshold elevation; the PAPI picture switches at the standard aiming angles of the four light units, 10 and 30 minutes of arc above and below the PAPI angle (AC 150/5340-30J Table 7-2; the AIM figure shows the five pictures, not the switching angles; the PAPI / VASI Approach Trainer uses the same picture); the line of sight to the PAPI is taken as the line to the threshold crossing point; still air, constant groundspeed, instant change from level flight to the descent.
VDP (AIM 5-4-5 h): a defined point on the final approach course of a non-precision straight-in approach from which a stabilised visual descent from the MDA to the runway touchdown point may begin; “The pilot should not descend below the MDA prior to reaching the VDP”; identified by DME or RNAV along-track distance; based on the lowest MDA and harmonised with the VGSI angle (or the VDA when there is no VGSI); it may not be published (obstacles, no distance information); pilots not equipped to receive it fly the approach as though none were provided (h 2); between the VDP and the MAP a descent may be inadvisable or impossible (h 3). Threshold crossing height: typically 30 to 50 ft (m 5 (c)).
Computed here: (1) charted-style VDP = (MDA − TDZE − TCH) ÷ (6,076 × tan PAPI angle) NM, charted to 0.1 NM; (2) the IFR Trainer’s Descent method = HAT ÷ (6,076 × tan angle) to the touchdown point (same results as its Descent module, checked); (3) the IPH rule HAT ÷ 300 (“To verify the aircraft is on an approximate three degree glidepath, use a calculation of 300 feet to 1 NM”; MDA 800 ft over a 400 ft TDZE → “approximately 1.3 NM” — scenario 1). Your descent: angle = atan((MDA − TDZE − TCH) ÷ distance); descent rate = 6,076 × tan(angle) × groundspeed ÷ 60; DME = distance + station offset; time from the FAF = (FAF − VDP) ÷ groundspeed.
PAPI picture (AIM 2-1-2 b and FIG 2-1-5, four light units): more than 3.5° four white (high); 3.2° three white one red (slightly high); 3° two and two (on glide path); 2.8° one white three red (slightly low); less than 2.5° four red (low) — modelled relative to the PAPI’s own angle, switching at the standard aiming angles of AC 150/5340-30J Table 7-2 (±10′ and ±30′). Descent rate limit on final: about 1,000 ft/min (IPH ch. 4 “Maximum Acceptable Descent Rates”). Challenge grade: within 0.25° of the PAPI angle good, within 0.6° fair (a platform training convention, not an FAA figure).
- Aeronautical Information Manual (effective 9 July 2026), para. 5-4-5 h (visual descent point: definition, do not descend below the MDA before the VDP, identified by DME or RNAV along-track distance, based on the lowest MDA and harmonized with the VGSI angle or the procedure VDA, may not be published), h 1–h 3, k (VDA advisory), m 5 (c) (threshold crossing height typically 30 to 50 ft), m 7 (b) (VDPs apply to LP or LNAV minima)
- Aeronautical Information Manual, para. 2-1-2 b and FIG 2-1-5 (PAPI: high more than 3.5°, slightly high 3.2°, on glide path 3°, slightly low 2.8°, low less than 2.5°; four light units); FAA Advisory Circular 150/5340-30J (12 Feb 2018, active), Table 7-2 (standard aiming of the four light units: 30 and 10 minutes of arc above and below the glide path) - the angles where the picture changes
- FAA Instrument Procedures Handbook, FAA-H-8083-16B (2017), ch. 4 Descent Rates and Glidepaths for Nonprecision Approaches (300 ft per NM; MDA 800 ft over a 400 ft TDZE reached about 1.3 NM from the threshold; if no VDP is annotated, calculate a normal descent point to the TDZ; more than about 1,000 fpm unacceptable below 1,000 ft AGL)
- FAA Advisory Circular 120-108A (2023), 3.10 approaches with a VDP (flying the VDA crosses the MDA at or beyond the VDP; dive and drive levels at the MDA to the VDP)
- Cross-tool: the visual descent point, the 300 ft per NM rule and the angle from a point on the MDA are the same calculations as the IFR Trainer's Descent module, identical results checked; the descent rate is the Step-Down Fix / Minimum Altitude calculation
- Model choices of this tool (stated on the page): schematic profile; touchdown zone elevation taken as the threshold elevation; PAPI picture switching at the standard aiming angles of AC 150/5340-30J Table 7-2 (the same picture as the PAPI / VASI Approach Trainer); line of sight to the PAPI taken as the line to the threshold crossing point; still air; challenge grade bands are a platform training convention