14.1 Visual Descent Point (VDP) & Circling Approaches

Visual Descent Point (VDP) & Circling Approaches

Quick Answer: A Visual Descent Point (VDP) is a defined point on the final approach course of a non-precision straight-in approach from which a normal stabilized $3^\circ$ descent from the Minimum Descent Altitude (MDA) to the runway touchdown point may begin. Calculated as $\text{Distance (NM)} = \text{HAT} \div 300$ or $\text{Time to subtract from FAF-to-MAP} = \text{HAT} \times 0.1\text{ seconds}$, descending below MDA prior to the VDP is strictly prohibited. Circling approaches are required when the approach course is offset $> 30^\circ$ from the runway centerline (or $> 15^\circ$ for GPS) or the descent gradient exceeds $400\text{ ft/NM}$. Standard TERPS protected radii are Cat A: 1.3 NM, Cat B: 1.5 NM, Cat C: 1.7 NM, Cat D: 2.3 NM, while expanded TERPS (indicated by a negative C icon) enlarges these areas at higher field elevations to ensure $300\text{ ft}$ of obstacle clearance. If visual contact is lost during circling, immediately execute a missed approach climbing turn toward the landing runway.

The final segment of a non-precision instrument approach presents significant energy management and obstacle clearance challenges. Unlike precision approaches (ILS or LPV) that provide continuous vertical electronic guidance directly to a decision point, non-precision approaches (LOC, VOR, RNAV LNAV) rely on stepdown altitudes and a flat Minimum Descent Altitude (MDA).

Without proper planning, pilots often fly a "dive-and-drive" technique—descending rapidly to the MDA and leveling off until arriving at the Missed Approach Point (MAP). If the pilot breaks out at the MAP, attempting to land requires an excessively steep, unstabilized dive toward the runway threshold. To prevent this hazard and provide a stabilized transition from instrument flight to landing, the FAA established the Visual Descent Point (VDP) and defined rigorous criteria for Circling Approaches.

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The Visual Descent Point (VDP)

A Visual Descent Point (VDP) is a defined point on the final approach course of a non-precision straight-in approach procedure from which a normal descent from the MDA to the runway touchdown point may be commenced, provided the approach threshold of that runway, or approach lights, or other markings identifiable with the approach end of that runway are clearly visible to the pilot (AIM 5-4-5).

+-----------------------------------------------------------------------------------------+
|                        VISUAL DESCENT POINT (VDP) PROFILE GEOMETRY                      |
|                                                                                         |
|             Final Approach Fix (FAF)                                                    |
|                    ●                                                                    |
|                     \                                                                   |
|                      \  Descent on Final                                                |
|                       \                                                                 |
|                        ▼___________________ [ VDP ]                                     |
|                        Minimum Descent Alt (MDA)  \                                     |
|                        (Level Flight Segment)      \  Stabilized 3° Descent             |
|                                                     \  (HAT ÷ 300 ft/NM)                |
|                                                      \                                  |
|                                                       \          Missed Approach        |
|                                                        \          Point (MAP)           |
|                                                         ▼              ●                |
|  ══════════════════════════════════════════════════════[===]═══════════╧════            |
|                                                     Threshold   Touchdown Zone          |
|                                                                                         |
|  ◄─────────────────────── Distance = HAT ÷ 300 ────────►                                |
+-----------------------------------------------------------------------------------------+

Symbology and Publication

• Chart Symbol: Represented on the profile view of FAA instrument approach charts by a bold uppercase "V".
• Fix Identification: A VDP is identified by DME distance, an along-track distance (ATD) RNAV waypoint, or a cross-radial fix.
• Applicability: Published only on non-precision straight-in approaches. VDPs are never published on precision approaches (which have electronic glideslopes) or circling-only approaches.

Why Some Approaches Do Not Have a Published VDP

If a non-precision straight-in approach chart does not depict a "V" symbol, one of several conditions exists:

1. Obstacle Penetrations: An obstacle penetrates the visual descent surface ($20:1$ or $34:1$ obstacle clearance surface) between the MDA and the runway threshold.
2. Lack of Fix Identification: There is no DME, marker beacon, or RNAV fix available to positively identify the VDP location along the final approach course.
3. TERPS Clearance Restrictions: Terrain or airspace constraints prevent establishing a standard $3^\circ$ descent profile from the MDA.

[!WARNING] If an approach does not publish a VDP, pilots should exercise extreme caution when descending below the MDA. The absence of a published VDP often indicates that unseen obstacles penetrate the visual segment between the MDA and the runway threshold!

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VDP Mathematical Formulas & Calculations

When a VDP is not charted or when flying non-precision approaches, instrument pilots can compute their own Visual Descent Point using two primary methods:

+-----------------------------------------------------------------------------------------+
|                                VDP CALCULATION FORMULAS                                 |
|                                                                                         |
|  1. Distance Method (Distance in NM from runway threshold):                             |
|                                                                                         |
|                            Height Above Touchdown (HAT) in feet                         |
|         VDP Distance (NM) = ------------------------------------                        |
|                                             300                                         |
|                                                                                         |
|  2. Timing Method (Seconds to subtract from total FAF-to-MAP elapsed time):             |
|                                                                                         |
|         Seconds to Subtract = HAT (feet) x 0.1   (or HAT ÷ 10)                           |
+-----------------------------------------------------------------------------------------+

1. Distance Calculation: $\text{HAT} \div 300$

• Standard $3^\circ$ descent path equals approximately 318 feet per nautical mile ($6,076.1\text{ ft} \times \tan(3^\circ) \approx 318.4\text{ ft/NM}$). The FAA rounds this to 300 ft/NM for simplified cockpit mental math.
• Formula: $\text{Distance from Threshold (NM)} = \frac{\text{HAT (ft)}}{300}$

Worked Calculation Example 1:

• Approach: LOC Rwy 28
• MDA: $860\text{ ft MSL}$
• Touchdown Zone Elevation (TDZE): $260\text{ ft MSL}$
• $\text{Height Above Touchdown (HAT)} = 860 - 260 = 600\text{ ft}$ $\text{VDP Distance} = \frac{600\text{ ft}}{300\text{ ft/NM}} = \mathbf{2.0\text{ NM from threshold}}$
• Interpretation: The pilot must establish visual contact and begin descending from $860\text{ ft}$ at $2.0\text{ NM}$ from the runway threshold. If the DME station is co-located with the threshold, the VDP is at 2.0 DME.

2. Time Calculation: $\text{HAT} \times 0.1$

• When DME or GPS along-track distance is unavailable, the pilot calculates elapsed time from the Final Approach Fix (FAF) to the MAP and subtracts a time buffer.
• Formula: $\text{Time to Subtract (seconds)} = \text{HAT} \times 0.1 = \frac{\text{HAT}}{10}$ $\text{VDP Clock Time} = \text{Total FAF-to-MAP Time} - (\text{HAT} \times 0.1)$

Worked Calculation Example 2:

• Approach: VOR Rwy 16 (FAF to MAP distance = $4.5\text{ NM}$)
• Groundspeed on final: $90\text{ knots}$ (FAF-to-MAP time from table = $3\text{ min } 00\text{ sec} = 180\text{ seconds}$)
• $\text{HAT} = 450\text{ ft}$ $\text{Seconds to Subtract} = 450 \times 0.1 = 45\text{ seconds}$ $\text{VDP Target Time} = 180\text{ s} - 45\text{ s} = 135\text{ seconds } (\mathbf{2\text{ min } 15\text{ sec}} \text{ after FAF})$
• Interpretation: Start the timer when crossing the FAF. The VDP occurs at 2 minutes 15 seconds. If visual references are acquired by 2:15, initiate a $3^\circ$ descent; if not, maintain MDA until reaching the MAP at 3:00.

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Operational Rules Governing the VDP

+-----------------------------------------------------------------------------------------+
|                              VDP OPERATIONAL DECISION RULES                             |
|                                                                                         |
|  Situation                              | Mandatory Pilot Action                        |
|  -------------------------------------- | --------------------------------------------  |
|  Visual reference acquired BEFORE VDP   | Maintain MDA; DO NOT descend until VDP.       |
|  Visual reference acquired AT VDP       | Initiate normal 3° descent to landing.        |
|  Visual reference NOT acquired at VDP   | Continue level at MDA to MAP; do not descend! |
|  Visual reference acquired AFTER VDP    | Land ONLY if normal descent rate possible;    |
|                                         | otherwise execute missed approach at MAP.     |
+-----------------------------------------------------------------------------------------+

1. Prohibition on Early Descent Below MDA

• Under 14 CFR § 91.175, an aircraft is strictly prohibited from descending below the MDA prior to reaching the VDP, even if the approach lights or runway environment are visible miles before the VDP.
• Hazard: Descending early creates an abnormally flat, shallow descent profile. This dramatically increases the risk of Controlled Flight Into Terrain (CFIT) by penetrating obstacle clearance surfaces below the MDA.

2. Arrival at VDP Without Visual References

• If the aircraft reaches the VDP without establishing the required visual references under § 91.175(c), the pilot MUST NOT descend below MDA.
• However, reaching the VDP is NOT a missed approach trigger. The pilot is legally authorized to continue flying level at the MDA along the final approach course until reaching the Missed Approach Point (MAP).

3. Visual Acquisition After Passing VDP

• If visual references are acquired between the VDP and the MAP, descending to land will require a descent angle steeper than $3^\circ$ (often exceeding $800\text{--}1000\text{ FPM}$ in light aircraft).
• If a normal descent rate using normal maneuvers cannot be maintained to touch down within the touchdown zone, the pilot must not attempt a landing and must execute a missed approach at the MAP.

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Circling Approaches: Purpose & Designation

A Circling Approach is the visual maneuvering phase of an instrument approach procedure used to align an aircraft with a landing runway when a straight-in landing from that instrument approach is not possible or desirable.

+-----------------------------------------------------------------------------------------+
|                       WHEN IS AN APPROACH DESIGNATED CIRCLING-ONLY?                     |
|                                                                                         |
|  An approach is designated with a letter suffix (e.g., VOR-A, RNAV-B) when:             |
|                                                                                         |
|  1. Final Approach Course Offset:                                                       |
|     • Exceeds 30° alignment with the runway centerline (exceeds 15° for GPS/RNAV).      |
|                                                                                         |
|  2. Final Descent Gradient:                                                             |
|     • Exceeds 400 ft/NM (approx. 3.77° / 6.6%) from the FAF to the threshold.           |
|                                                                                         |
|  3. Unsurveyed Runway Environment:                                                      |
|     • Runway lacks published markings, lighting, or surveyed touchdown zone data.       |
+-----------------------------------------------------------------------------------------+

Naming Conventions for Circling-Only Approaches

• When an approach procedure does not meet straight-in criteria, the runway number is omitted from the title and replaced with a sequential alphabetical suffix starting with the letter "A" (e.g., VOR-A, VOR/DME-B, RNAV (GPS)-A).
• Suffix letters are assigned sequentially for each distinct circling approach designed for an airport, regardless of the NAVAID type.

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Aircraft Approach Categories (14 CFR § 97.3)

Instrument approach minimums and protected circling airspace boundaries are grouped into five distinct aircraft approach categories based on $1.3 \times V_{SO}$ (stall speed in the landing configuration) at the maximum certified landing weight:

[!IMPORTANT] Speed Category Operational Rule: If a pilot flies an approach or circling maneuver at an indicated airspeed higher than the aircraft's certified category speed (e.g., flying a Cat A Cessna 182 at $105\text{ KIAS}$ on downwind), the pilot MUST use the higher category minimums (Cat B). Operating at higher speeds increases turn radii and requires larger protected airspace!

TERPS Protected Circling Airspace Radii

Under United States Standard for Terminal Instrument Procedures (TERPS), procedure designers construct protected circling airspace by drawing circular arcs from the threshold of each usable runway and connecting the arcs with tangential lines.

+-----------------------------------------------------------------------------------------+
|                    TERPS PROTECTED CIRCLING AIRSPACE ARCS                               |
|                                                                                         |
|                   ┌──────────────────────────────────────────────┐                      |
|                .─'                                                '─.                   |
|             .─'             PROTECTED CIRCLING AIRSPACE              '─.                |
|           .'                                                            '.              |
|          /        Arc Radius (R)              Arc Radius (R)              \             |
|         │        ◄──────────────►            ◄──────────────►              │            |
|         │     ┌───●──────────────┐          ┌──────────────●───┐           │            |
|         │     │ Runway 09 End    │══════════│ Runway 27 End    │           │            |
|         │     └───●──────────────┘          └──────────────●───┘           │            |
|          \                                                                /             |
|           '.         Guarantees 300 ft Minimum Obstacle Clearance       .'              |
|             '─.                     (ROC)                            .─'                |
|                '─.                                                .─'                   |
|                   └──────────────────────────────────────────────┘                      |
+-----------------------------------------------------------------------------------------+

Minimum Obstacle Clearance

• Within the entire protected circling area, TERPS guarantees a minimum of 300 feet of Required Obstacle Clearance (ROC) above the highest obstacle.

Standard TERPS Circling Radii (Legacy Criteria)

Historically, TERPS defined static circling radii based solely on approach category, calculated for sea level standard temperature and zero wind with a $15^\circ$ bank angle:

• Category A: $1.3\text{ NM}$
• Category B: $1.5\text{ NM}$
• Category C: $1.7\text{ NM}$
• Category D: $2.3\text{ NM}$
• Category E: $4.5\text{ NM}$

Expanded TERPS Circling Radii (The Negative "C" Icon $\mathbf{\mathcal{C}}$)

• Why Expanded Criteria Were Introduced: At high-elevation airports, true airspeed (TAS) is substantially higher than indicated airspeed (IAS) for a given category. Higher TAS increases turn radius ($R = V^2 / (g \tan\theta)$), causing faster category aircraft (such as Cat C and D jets) to fly outside legacy protected airspace boundaries.
• The Icon: On approach charts designed under expanded criteria, a white "C" inside a black square (negative C: $\mathbf{\mathcal{C}}$) is printed next to the circling line of minimums.

+-----------------------------------------------------------------------------------------+
|                 EXPANDED TERPS CIRCLING RADII BY MDA ALTITUDE TIERS                     |
|                                                                                         |
|  Approach Cat | 1,000 ft or less | 1,001–3,000 ft | 3,001–5,000 ft | 5,001–7,000 ft     |
|  ------------ | ---------------- | -------------- | -------------- | ---------------    |
|  Category A   | 1.3 NM           | 1.3 NM         | 1.4 NM         | 1.5 NM             |
|  Category B   | 1.7 NM           | 1.8 NM         | 1.8 NM         | 1.9 NM             |
|  Category C   | 2.7 NM           | 2.8 NM         | 2.9 NM         | 3.1 NM             |
|  Category D   | 3.6 NM           | 3.7 NM         | 3.8 NM         | 4.0 NM             |
|  Category E   | 4.5 NM           | 4.6 NM         | 4.8 NM         | 5.0 NM             |
+-----------------------------------------------------------------------------------------+

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Circling Maneuver Rules & Lost Visual Contact Procedures

When executing a circling maneuver in IMC conditions transitioning to visual:

+-----------------------------------------------------------------------------------------+
|                        LOST VISUAL CONTACT DURING CIRCLING                              |
|                                                                                         |
|             1. LOST VISUAL CONTACT AT ANY POINT IN CIRCLING                             |
|                                    │                                                    |
|                                    ▼                                                    |
|             2. INITIATE IMMEDIATE MISSED APPROACH (FULL POWER & CLIMB)                  |
|                                    │                                                    |
|                                    ▼                                                    |
|             3. MAKE AN INITIAL CLIMBING TURN TOWARD LANDING RUNWAY                      |
|                                    │                                                    |
|                                    ▼                                                    |
|             4. FLY OVER AIRPORT & INTERCEPT PUBLISHED MISSED APPROACH TRACK             |
+-----------------------------------------------------------------------------------------+

Step-by-Step Circling Rules:

1. Maintain MDA: The pilot must remain at or above the circling MDA until the aircraft is continuously in a position from which a descent to landing can be made on the intended runway at a normal rate of descent using normal maneuvers.
2. Visual Contact: The runway environment must remain in sight at all times.
3. Maneuvering Airspace: The entire visual circling pattern must be confined within the published protected circling radius.

The Lost Visual Contact Golden Rule

• If visual reference with the runway environment is lost at any point during a circling maneuver (e.g., entering a low scud cloud or thick fog on downwind or base):
  1. Immediately initiate a missed approach (apply full go-around power and pitch for climb).
  2. Make an immediate climbing turn TOWARD the landing runway centerline.
  3. Continue the climbing turn until established over the airport, then track outbound along the published missed approach course for the instrument approach procedure just flown.

[!CAUTION] Why Turn Toward the Landing Runway? Turning away from the airport or attempting to circle blindly outside the pattern guarantees flight into un-surveyed obstacles. Turning toward the landing runway ensures the aircraft remains directly over the surveyed, protected airport environment while gaining altitude, safely intercepting the missed approach corridor.