Pilots flying a precision instrument approach have course deviation and glide data to guide them all the way. But what triggers a non-precision approach, and how do pilots flying this type of approach know when and where to begin their final descent so they can make a safe landing? The optical descent point is part of this equation.
What is Visual Descent Point (VDP)?
The official AIM definition of a visual descent point or VDP is "the specified point on the final approach path of a non-precision level approach from which a normal descent from the MDA to the landing point on the runway may be initiated, provided that the approach threshold and runway or approach lights or other markings identified with the approach end of that runway are clearly visible to the pilot.'
As a refresher, in the definition above, MDA is the minimum descent altitude - the lowest altitude you can ultimately descend to during a standard instrument approach procedure (SIAP) without electronic pitch secured.
During the descent, you must remain at or above the minimum descent altitude until you have the visibility required to descend safely and obtain one of the approved visual references. You also need to be able to make a "normal" (read: not dangerously steep) descent. The visual descent point is the position from which you can descend from the MDA while maintaining a 3 degree glide path and land on the landing point.
Types of energy access procedures
When you are on final approach and preparing to land, you need a controlled, orchestrated means of coordinating both the course and glide path during descent to land safely on the runway landing point.
For pilots flying under Instrument Flight Rules (IFR), there are three types of Instrument Terminal Procedures (TERPS) or Instrument Approach Procedures (IAP) that can be used during an instrument landing.
Precision Approach (PA)
Precise approximation (PA) is, as you might expect from the name, the most accurate. It uses a navigation system that provides data on course deviation and slip. ILS (Instrument Landing System) is usually used to guide precision approaches.
Approach with vertical guidance (APV)
Another type of TERPS is the approach with vertical guidance (APV). The navigation system used for the APV approach provides course deviation and glide data similar to PA, but not to such a carefully calibrated standard. Therefore, the vertical guidance provided by APV is less accurate than that of PA. Approach with vertical guidance is supported by LNAV/VNAV systems.
Imprecise approach
The last type of TERPS is the imprecise approach (NPA). For this instrument-based approach, the pilot's navigation system provides course deviation feedback but no glidepath deviation data. The VOR system is usually used to support and guide non-precision approaches.
The continuous descent finite approximation (CDFA) is the newer, preferred method of controlling the rate of descent in a non-precision approach, and CDFAs have been published for most non-precision approaches. Where a CDFA is not available, pilots may land using a descent approach or the dive-and-drive method to descend to the minimum descent altitude as soon as they reach the final approach fix (FAF).
In the CDFA or Dive and Drive method, the Visual Descent Point (VDP) is located on the glide path and plays a key role in guiding the landing process.
What is the purpose of visual descent point (VDP)?
An imprecise approach can be dangerous. The FAA and NTSB have identified unstabilized approaches as one of the primary causes of imprecise approach accidents.
When performing an imprecise approach, some of the potential risks include:
- Dive too steep and you can't level up
- Hitting an obstacle while descending
- Below the Minimum Descent Altitude (MDA) very quickly
- Landing outside the safe landing point
By starting the final descent from the minimum descent altitude (MDA) while reaching the visual descent point and acquiring a visual reference, you will normally put yourself on a 3 degree glide path to the landing point. This is the same slope that most precision approaches use. Using a visual descent point to begin the final descent helps you avoid too steep or too shallow a final descent angle.
How to find the visual descent point (VDP)?
If published, the visual descent point (VDP) is indicated by the letter "V" on the vertical profile of many approach panels. Pilots can also calculate it manually. If you must manually determine the VDP position for your approach, use the equation below to give you the distance from the landing point to the visual descent point in nautical miles (nm).
Note that the above equation is a pilot's "rule of thumb" mathematical estimate, which assumes about 300 feet per nautical mile for a 3-degree glide path. The actual trigonometric value is 318 feet, but the easiest estimate to work with is only 18 feet, or 6% less, and this is accurate and conservative enough for VDP calculation purposes. Altitude Above Touchdown, or HAT, should be listed on your chart and can be calculated using:
Once you know the distance from the visual descent point to the landing zone, you can subtract the distance from the runway threshold to the landing zone. This gives you the distance of the VDP from the approach end of the runway.
In most cases you will use distance measuring equipment (DME) to alert you to the location of the VDP. If your DME is not working, it is recommended that you approach it as if there is no VDP, since you do not have the equipment to detect it.
A visual glide slope indicator (VGSI) can also be used as a visual aid for pilots flying an imprecise instrument approach. Note that if visibility is at or slightly above the minimum, pilots may not be able to see the VGSI when they reach the visual descent point, since the VGSI is behind the missed approach point (MAP).
It is important to realize that in many cases, if the VDP is not deployed, it is because there is terrain or other obstacles that could prevent a safe descent. In this case, calculate the location of your visual descent point, but be absolutely sure that you have sufficient visibility to see potential hazards before you begin your descent from the MDA. If there are known obstacles, the chart will say "visual segment - obstacles" to warn you that you may need to change your approach to avoid hazards.
What if you lose your visual descent point (VDP)?
Note that the following three criteria must be met in order to be allowed to descend below the minimum descent height:
- Be in a permanent position for a normal descent and landing on the designated runway
- Have the necessary visibility for a safe descent
- Pay attention to the runway environment
If all the above criteria are met, you can start the descent when you reach the visual descent point. If not, you should not be eligible for MDA until the criteria are met. If the criteria are not met by the time you reach the point of visual descent, this is called a disappearance or flight outside the VDP.
If you lose the visual descent point, you can technically continue to fly at minimum descent altitude (MDA) until you reach the missed approach point (MAP). If you still have no visibility, cannot or are unable to pick up at least one of the visual reference points and begin your final descent until you reach the MAP, then you must perform a missed approach procedure and go around. Never initiate a descent from the minimum descent altitude (MDA) past the missed approach point (MAP). First, it's illegal, and second, your angle will be too steep or your landing point will be too far down the runway for safety.
For added backup, some pilots like to use the visual descent point as the missed approach point. By making the decision to call for a missed approach if they do not have sufficient visibility, are out of position, or cannot see their VDP visual indicators, pilots give themselves enough time to abort the landing attempt before passing the missed approach point.
Ultimately, the decision on whether to report a missed approach to VDP or MAP is up to the pilot. If you cannot descend to VDP because you do not meet the three required criteria, but conditions improve and you meet the criteria before reaching MAP, it is up to the pilot to continue the landing. Realizing that any descent that begins beyond the visual descent point will be steeper than the normal 3 degrees, pilots must consider aircraft type, configuration, airspeed, altitude, rate of descent, turn, and runway length and then make the appropriate decision. If in doubt, err on the side of caution and miss the call.
Can you descend below the minimum descent altitude before reaching VDP?
There has been much debate among pilots as to whether you absolutely must wait until you reach the visual descent point before descending below MDA, or whether waiting until VDP is just a guideline and suggestion that pilots are free to ignore if the situation warrants.
AIM formulation andCFR 91.175 c3on when pilots can descend below the MDA confirms that pilots can descend only when they meet the three criteria for descending below the MDA. It does not clarify anything about how this relates to the optical descent point.
In theirsDescent to MDA or DH and beyondHowever, in describing when to descend, the FAA specifically states, "Do not descend below MDA before reaching VDP."
Packaged food
The Visual Descent Point (VDP) is a reference point used by pilots flying non-precision instrument landings. This point is at the minimum descent altitude (MDA) and indicates the position from which the pilot can begin the final descent to landing, provided he can land, has the necessary visibility and has visual references with the runway environment. A continuous rate of descent from the VDP to the landing point typically places the pilot at the same 3-degree pitch used by pilots flying a precision approach.
If you are out of position, have no visibility and/or have not acquired visual references until you reach the visual descent point, you may continue to fly at the minimum descent altitude until you reach the missed approach point (MAP) in which case you must call a missed approach and execute a turn. Depending on the aircraft, experience level and conditions, some pilots choose to fly more conservatively and call for a missed if they cannot descend after reaching the visual descent point instead of waiting until they reach the missed approach point.
Pilots may descend below the minimum descent altitude at the visual descent point or between the visual descent point and the missed approach point if they can safely do so. The FAA instructs pilots to avoid descending below the minimum descent altitude until they reach the visual descent point. This helps minimize the risk of hitting the ground and obstacles due to premature descent.
A thorough understanding of the purpose, location and use of the visual descent point will help IFR pilots flying a non-precision approach to do so safely and smoothly. Review instrument approach procedures and other IFR specifics sInstrument pilot's manual. For a clear, simple visual presentation of understanding and using the optical descent point, check out Larry Epley's Quick and ConciseVDP Explanation.
Read more about Visual Descent Point (VDP) and other flight training topics on ourFlightEducational material: Private pilot collection.
FAQs
Visual Descent Point (VDP): What exactly is it? ›
The Visual Descent Point (VDP), identified by the symbol (V), is a defined point on the final approach course of a nonprecision straight-in approach procedure from which a stabilized visual descent from the MDA to the runway touchdown point may be commenced.
What is the VDP visual descent point? ›VDP. The Visual Descent Point (VDP) is a defined point on a straight-in, non-precision approach from which you can descend below the MDA, as long as you have the required visual reference. If a VDP is available, it will be indicated by a "v" on the profile view portion of the instrument approach procedure chart.
What is the VDP explanation? ›According to the AIM, "the VDP is a defined point on the final approach course of a non-precision straight-in approach procedure from which normal descent from the MDA to the runway touchdown point may be commenced."
How is a VDP calculated? ›A Visual Descent Point is found by subtracting the touchdown zone from the Minimum Descent Altitude and dividing the result by 300.
What is a VDA in aviation? ›Visual Descent Angles (VDAs) are the angle between the runway threshold at the crossing height (TCH) and the minimum altitude at the final approach fix. Stepdown fixes are normally located so the VDA crosses the fix at or above the fix minimum altitude.
What is the difference between MDA and DA? ›Decision Altitude
In practical terms, that means approaches with a glide slope (ILS), and approaches with a glide path (LPV, LNAV/VNAV). DA's are different than MDAs. MDAs are absolute floors, but when flying to a DA, you make your "continue-to-land" or "go missed" decision at DA, while you remain on the glideslope.
Visual Approach Slope Indicator (VASI) Precision Approach Path Indicator (PAPI) Pulsating Visual Approach Slope Indicator (PVASI) Three-color Visual Approach Slope Indicator (T-VASI)
Why do we need VDP? ›A Vulnerability Disclosure Policy (VDP) is a secure and structured channel that allows anyone to report security issues and vulnerabilities to exposed organisations.
How does VDP ensure security? ›Ultimately, the VDP Platform enables agencies to receive actionable vulnerability information and collaborate with the public to improve the security of their internet-accessible systems.
What is a VDP application? ›VOLUNTARY DISCLOSURE RELIEF
SARS allows taxpayers to avoid criminal prosecution and regularise their tax affairs by making a disclosure under the VDP. A successful VDP application allows for an applicant to receive waiver of penalties and to settle outstanding tax liabilities with SARS.
How long does a VDP take? ›
HOW LONG DOES IT TAKE TO PROCESS A VDP APPLICATION? SARS is inundated with VDP applications and the current average turnaround time of a VDP application, according to SARS, is 201 working days.
How do you know when to start descending? ›In feet, according to the calculation, the TOD is 667,840 ft and in nautical miles, it is 110 NM. So, in normal circumstances, the pilots should begin their descent 110 NM from the target or the landing aerodrome. The use of trigonometry will always give the most accurate value for the top of descent.
What is the 60 to 1 rule VDP? ›In air navigation, the 1 in 60 rule is a rule of thumb which states that if a pilot has traveled sixty miles then an error in track of one mile is approximately a 1° error in heading, and proportionately more for larger errors.
What is VDA altitude? ›The VDA is calculated from the Final Approach Fix (FAF) altitude to the threshold crossing height (TCH). The optimum NPA descent angle (VDA) is 3.0 degrees14. On approaches with step-down fixes, the goal is to publish a VDA that keeps the aircraft's vertical path above the step-down fixes.
What is the minimum descent altitude? ›MINIMUM DESCENT ALTITUDE (MDA)- The lowest altitude, expressed in feet above mean sea level, to which descent is authorized on final approach or during circle-to-land maneuvering in execution of a standard instrument approach procedure where no electronic glideslope is provided.
What is VDA legal term? ›In an effort to accomplish this objective, a Voluntary Disclosure Agreement (VDA) is available to taxpayers to report previously unpaid or underpaid taxes to the Comptroller's office.
Why add 50 feet to MDA? ›If flying a precision approach you make the decision to go around at the DA which means that you will descend below this altitude during the missed approach procedure. It is recommended that you add 50ft for PEC to avoid altimeter errors which could mean you descending into a dangerous position.
What does DH mean in aviation? ›Decision height (DH) is a specified height above the ground in an instrument approach procedure at which the pilot must decide whether to initiate an immediate missed approach if the pilot does not see the required visual reference, or to continue the approach. Decision height is expressed in feet above ground level.
When can you descend from MDA? ›Specifically, the rule states that once a pilot, who is established at MDA, sees the approach lights he can descend below the MDA to 100 feet above the touchdown zone elevation (TDZE):
What is the difference between RVR and visibility? ›RVR, in contrast to prevailing or runway visibility, is based on what a pilot in a moving aircraft should see looking down the runway. RVR is horizontal visual range, not slant visual range.
What is a PAPI light? ›
The PAPI system is the current standard Visual Glide Slope Indicator (VGSI) consisting of four light boxes arranged perpendicular to the edge of the runway. It projects a pattern of red and white lights that provide visual approach slope information.
What are the three main types of VOR indicators? ›There are three types of VOR navigational stations: VOR (just the VOR), VOR-DME (VOR plus distance measuring equipment), and vortac (VOR plus the military's tactical air navigation system).
What are VDP vulnerabilities? ›The Vulnerability Disclosure Program (VDP) is a centralized process through which a company gets security expert reports about security flows in its publicly accessible, web-facing assets. VDP increases a business' security posture by involving the cybersecurity community.
What is the difference between VDP and bug bounty? ›VDPs usually have a broader scope than bug bounties, which makes sense since the client doesn't pay for vulnerabilities. In contrast, a company may restrict the scope of bug bounties to testing “critical infrastructure” (ie. important applications and assets) for severe vulnerabilities.
What is the difference between VDP and BBP? ›A VDP is a structured method for third parties, researchers, and ethical hackers to report vulnerabilities easily. A bug bounty is a reward that organizations offer to ethical hackers for discovering bugs. Organizations use a VDP to establish clear guidelines for anyone who discovers vulnerabilities.
What does VDP mean in cyber security? ›This Vulnerability Disclosure Policy (VDP) provides guidelines for the cybersecurity research community and members of the general public (hereafter referred to as researchers) on conducting good faith vulnerability discovery activities directed at public facing DOJ websites and services.
What is the full form of VDP in cyber security? ›Uncover critical vulnerabilities that conventional tools miss. Attack surface management informed by hacker insights. Reduce risk with a vulnerability disclosure program (VDP).
What three types of security features are used to ensure data security? ›Firewalls, password protection, and multi-factor authentication are all types of data security measures typically employed.
What does voluntary disclosure usually include? ›Voluntary disclosure by an issuer should address any information, event, action, or other situation affecting an issuer's obligations, credit, or operating information that the issuer believes is important to municipal market participants. This may include negative or positive information.
What is the penalty for tax evasion in South Africa? ›The administrative non-compliance penalty for the failure to submit a return comprises fixed amount penalties based on a taxpayer's taxable income and can range from R250 up to R16 000 a month for each month that the non-compliance continues.
Who qualifies as a small business corporation in South Africa? ›
Small Business Corporation (SBC)
Small businesses with an annual turnover of up to R20 million may qualify to pay Income Tax at a reduced tax rate. If you indicate that you are a small business on your Income Tax Return (ITR14), and meet all the requirements, the reduced rates will be applied automatically.
A certificate issued by uni-assist which you submit directly to the university when you apply there. The VPD is a certificate issued by uni-assist which you submit directly to the university when you apply there.
What is the 3 6 rule in aviation? ›For larger aircraft, typically people use some form of the 3/6 Rule: 3 times the altitude (in thousands of feet) you have to lose is the distance back to start the descent; 6 times your groundspeed is your descent rate.
What is the 3 to 1 rule for descent? ›A general rule of thumb for initial IFR descent planning in jets is the 3 to 1 formula. This means that it takes 3 NM to descend 1,000 feet. If an airplane is at FL 310 and the approach gate or initial approach fix is at 6,000 feet, the initial descent requirement equals 25,000 feet (31,000–6,000).
How far from airport do planes start descent? ›A: Normally an airliner will begin its descent around 100 to 120 miles from the destination (assuming the cruising altitude is above 30,000 feet).
What is the rule of thumb VDP? ›Calculating the VDP
If you work out the trigonometry you would find that descending 3 degrees per NM equates to a descent of approximately 300 feet per NM. Using this knowledge a “rule of thumb” calculation for computing the VDP is: Visual Descent Point = Height Above touchdown/ 300 feet.
Remember, the 1 in 60 rule states that starting out, one degree off means winding up one mile off 60 miles later.
What is the one third rule in aviation? ›In aviation, the rule of three or "3:1 rule of descent" is a rule of thumb that 3 nautical miles (5.6 km) of travel should be allowed for every 1,000 feet (300 m) of descent.
What is the FAA altitude rule? ›An altitude of 500 feet above the surface, except over open water or sparsely populated areas. In those cases, the aircraft may not be operated closer than 500 feet to any person, vessel, vehicle, or structure.
What is the maximum descent rate final approach? ›Operational experience and research have shown that a descent rate of greater than approximately 1,000 FPM is unacceptable during the final stages of an approach (below 1,000 feet AGL). This is due to a human perceptual limitation that is independent of the type of airplane or helicopter.
What does 34 1 not clear mean? ›
> The FAA surveys several clearance planes when evaluating an approach. Obstacle penetrations may cause them to increase restrictions to the approach such as higher visibility or prohibit operations to a runway at night. These are charted in the profile view as “34:1 is not clear.”
What is the descent rate for landing 737? ›This configuration should hold airspeed with a good descent angle toward the runway. Use small power adjustments and pitch changes to stay on the glidepath. You're looking for a descent rate of about 700 fpm. Before landing, make sure the speed brake handle is in the ARM position.
What rate of descent is considered hard landing? ›That said, based on certification criteria, the hard landing threshold is the same for virtually all commercial pattern aircraft and is expressed either as a touchdown 'g' loading of 2.6, or as a touchdown rate of descent exceeding 600 feet per minute (fpm), for landing weights up to the certified maximum for the ...
What is a 3 degree descent? ›A three-degree glideslope refers to the angle of descent an aircraft will use. In other words, the angle between the flight path and the ground. The larger the angle, the steeper the descent, and the higher the rate of descent. A commercial aircraft will typically descend at between 1,500 and 3,000 feet per minute.
What are the different types of VDA? ›There are two types of VDAs for Windows machines: VDA for multi-session OS and VDA for single-session OS.
What is the full form of VDA format? ›What is VDA? VDA stands for Verband der Automobilindustrie, the German Automotive Industry Association. The VDA maintain a series of fixed format messages that describe business documents typically exchanged between automotive manufacturers and suppliers.
What does VDA mean in voluntary disclosure? ›Submitting a voluntary disclosure agreement (VDA)—an agreement between your business and its jurisdictions to limit lookback periods and generally waive penalties during tax reviews—can be one of the most effective ways to voluntarily meet compliance obligations.
How do you calculate a VDP in miles and in time? ›You can calculate your own visual descent point (VDP), since one isn't provided for you, by taking the height above touchdown (600 ft. in this case) and dividing it by 300 ft/NM. This gives you 2.0 miles from the runway.
What is the Minimum Descent Altitude? ›MINIMUM DESCENT ALTITUDE (MDA)- The lowest altitude, expressed in feet above mean sea level, to which descent is authorized on final approach or during circle-to-land maneuvering in execution of a standard instrument approach procedure where no electronic glideslope is provided.
What is the difference between DA and DH in aviation? ›Definition. Decision altitude (DA) is referenced to mean sea level and decision height (DH) is referenced to the threshold elevation.
How do you calculate variable cost per mile? ›
Divide your total expenses by the total number of miles driven, and the result is your cost per mile.
How do you calculate exact mileage? ›The easiest way to calculate your gas mileage is to simply divide the number of miles traveled by the number of gallons of gas your vehicle took to refill. In sum, that's miles driven divided by gallons of gas used.
How is descent calculated? ›If you multiply your descent angle (1 degree) by your miles-per-minute, then add two zeros to the end (x 100), you'll have your FPM descent rate. So in this example, if you're flying at 120 knots, you're traveling 2 miles-per-minute (MPM) (120/60=2).
What is the descent rate for VFR? ›For a light VFR aircraft, the usual descent rate can be taken as -500ft/min. That means you will lose 500ft in 1 minute.
What is the maximum acceptable descent rate? ›Operational experience and research have shown that a descent rate of greater than approximately 1,000 FPM is unacceptable during the final stages of an approach (below 1,000 feet AGL). This is due to a human perceptual limitation that is independent of the type of airplane or helicopter.
What is the 3 6 descent rule? ›For larger aircraft, typically people use some form of the 3/6 Rule: 3 times the altitude (in thousands of feet) you have to lose is the distance back to start the descent; 6 times your groundspeed is your descent rate.
What is the decision altitude for LPV? ›LPV minima may have a decision altitude (DA) as low as 200 feet height above touchdown zone elevation with associated visibility minimums as low as 1/2 mile, when the terrain and airport infrastructure support the lowest allowable minima.
What is DTD in aviation? ›Distance to Touchdown | SKYbrary Aviation Safety.