Continuous Descent Final Approach (CDFA)

Flying a Continuous Descent Final Approach (CDFA) eliminates the MDA level off, puts the airplane in a position to land when the runway is sighted, and forces you to go around if the runway is not sighted before a normal visual descent point. It is easier to fly than a dive and drive approach and you don't need any special equipment. But technology does help.

Note: The examples on this page are more than likely out of date. Many countries are adopting the CDFA technique and making changes as they fine tune. You need to check their AIP or the Jeppesen State pages to ensure you have the latest rules for any country.

1 — Questions and answers

2 — Determining a Derived Decision Altitude (DDA)

3 — Leaving the Final Approach Fix (FAF)

4 — When to go missed approach

5 — Examples

What is it?

A continuous descent final approach is what you do for every straight-in ILS and what you attempt to do for every visual straight-in approach: you hit the glide path and start down on an angle that ends up in the touchdown zone of the runway. You can also do this when in instrument conditions flying a non-precision approach, which we are probably better off calling an "approach without vertical guidance."

Why is it needed?

Some of us began our instrument jet experience without the benefit of an autopilot or flight director and flying an approach without vertical guidance was an invitation to making fatal mistakes. Even with the best technology, flying an approach without vertical guidance can be a problem:

• We often pull the throttles and head down from the final approach fix at 1,000 feet per minute or more, knowing we have to level off at the Minimum Descent Altitude. But we seldom fly without distractions and some pilots have missed this step right into the ground.

Example: American Airlines 1572.

• Even if you succeed at leveling off at the MDA, you need to keep the airplane there until the runway is spotted and the airplane is in a position to land.

Example: Corporate Airlines 5966.

• In a low visibility approach we can't always perceive the angle to the runway and it can be tempting to push the nose over the minute we see the runway. But if you do this too early you don't have a good idea of the descent rate required or you could lose sight of the runway.

Example: Crossair 3597.

• If you are level at the MDA you should have an idea of where you will intercept a normal glide path to the touchdown zone. Once you've passed this point, you really ought to go missed approach. You could be tempted to try the landing, not really knowing how much pavement you have ahead of you.

Example: Korean Air 2033.

Is it Required?

In some countries: yes. In other countries: it is recommended but not mandatory.

ICAO Preferred Technique.

EU Required.

FAA Recommended

Required by Some Countries.

Many countries do require CDFA techniques be used for flying approaches without vertical guidance, but the application of the technique is not consistent. Some countries list a CDFA approach with "CDFA" in the minimums section while others use "DA" or "DA/MDA" to signify such approaches. Even the countries that list "CDFA" are not consistent about the meaning. The only way to ensure you are following the rules of the host nation is to look it up in the country's Aeronautical Information Publication or the Jeppesen Airways Manual ATC pages.

Do you need special equipment?

If you have the equipment to fly an instrument approach, you have what you need to fly a continuous descent final approach. The more technology you have, however, the easier it will be to do that.

What kind of approach is suitable for a CDFA?

Published Angle — Chart Legends

In the United States there is a stipulation in AC 120-108 requiring that you see a published angle on the chart. The presence of the angle varies with approach type and is also depicted differently between FAA and Jeppesen charts. There are four variations, described below.

24. Altitudes that correspond to the VDA

26. Pull-up along the VDA at the DA/MDA is depicted relative to the missed approach point.

28. A dotted gray line indicates the continuance of the VDA below the DA/MDA.
29. Visual flight track is shown when the missed approach point is prior to the runway threshold.

14. Pull-up representing the DA/MDA or when reaching the descent limit along the GS/VDA.
15. Pull-up arrow associated to a non-precision approach not using a CDFA technique.

Published Angle — Examples with Glide Slopes

On an FAA chart, an RNAV(GPS) will contain the glide slope angle in the profile view.

On a Jeppesen chart, an RNAV(GPS) will be depicted with glide feathers in the profile view.

Published Angle — Examples with Vertical Descent Angles

On an FAA chart, a non-RNAV or RNAV without vertical guidance will contain the vertical descent angle in the profile view.

On a Jeppesen chart, a non-RNAV or RNAV without vertical guidance will depict the vertical descent angle with a dotted gray line below the MDA in the profile view.

Vertical Path Angle — Limitations

AC 120-108 does not impose a maximum vertical path angle, per se, but if you have OpSpec, MSpec, or LOA C073 you are already familiar with a VNAV DA(H) in lieu of MDA(H) provision that limits you to 3.77° (Category A, B, and C) or 3.5° (Category D and E). You really should adopt those limits for CDFA as well.

More about this: Vertical Navigation (VNAV).

The MDA, under most cases, is still an altitude you cannot go below. The CDFA technique adds an altitude pad to account for the aircraft's tendency to go below the altitude at which the missed approach is initiated, usually due to autopilot reaction time. The new altitude, that resulting from the addition of this pad to the MDA, is known as the Derived Decision Altitude (DDA).

Increment Added to MDA.

C073 is now available also as a Letter of Authorization. These approaches, those with the "Only Authorized Operators" ball note, take into consideration the aircraft's momentary dip below the MDA.

More about this: Vertical Navigation (VNAV).

Some countries add the altitude pad into the approach minimums, pilots need not "double add." Examples below.

G450 Example: Autopilot Performance.

While some countries specify the method used to determine the DDA, most do not. In the case of a G450, pilots will add 60' to the MDA to determine the DDA.

Aircraft Configuration

The objective of CDFA is to leave the final approach fix fully configured, on speed, and ready to land. You should not have to destabilize the aircraft by making airspeed or trim adjustments when spotting the runway. GV and G550 pilots often withhold the last increment of flaps as a courtesy to faster moving aircraft, but if flying a CDFA in instrument conditions, it may be wiser to configure earlier.

Methodology: High Tech

Some aircraft allow a CDFA be flown with ILS-like indications so that procedures can be identical. Others may require adjustments, such as lowering the altitude select to field elevation. The closer CDFA procedures can be to an ILS, the better. Pilots simply follow the needles down to minimums, being mindful of the decision altitude. (In either case, pilots should consult their aircraft manuals and practice these procedures in a simulator until comfortable.)

The G450 can adhere to CDFA techniques by either:

• Using LNAV/VNAV on most non-precision approaches, setting the altitude preselector to the minimum descent altitude plus 60 feet. If the runway is not sighted visually or using EVS, the autopilot would initiate a level off prior to the MDA/DA and the pilot would then accomplish a missed approach. If the runway is sighted, the pilot would press APPR which turns the VPATH into a VGP, causing the autopilot to ignore the altitude preselector. (At this point the altitude preselector would be set to the missed approach altitude.)
• Using APPR on most non-precision approaches, setting the altitude preselector to missed approach altitude and treating the MDA plus 60 feet as you would an ILS decision height, taking care to go around if you do not have what it takes to land at DA + 60 feet.

While the first method prevents you from going below minimums if you attain visual contact, it increases your work load if you do. I recommend the second method, making sure both pilots understand it will be flown like an ILS.

Methodology: Low Tech

If you don't have an FMS that does all this for you, or if you are flying an approach that prevents your FMS from doing all this for you, this table gives you an idea of what vertical descent rate you are going to need. If you don't have the table, you can approximate a 3° angle of descent by dividing your groundspeed by 2 and multiplying that by ten. A 120 knot ground speed, for example, yields 600 fpm.

You can check your progress during the approach by placing tick marks at each mile from the final approach fix to the missed approach point with the appropriate altitude. A 3° glide path should lose 318' every nautical mile. If, for example, the final approach fix altitude is 2,000 feet, you should be at 1,682' after one mile, 1,364' after two miles, 1,046' after three miles, and so on. You can figure these out during your approach briefing, marking each target on the approach plate.

Descent to MDA/DA.

The CDFA places the aircraft right on glide path in a position to land in the touchdown zone of the runway. If the runway is sighted after this point, the aircraft will be too far down the runway to make that happen and a missed approach will be needed. This eliminates the judgment calls when sighting the runway early or late.

MDA Published with GS — KLAF RNAV(GPS) Rwy 28

This approach gives you several options, depending on aircraft capability and crew training:

• If the aircraft and crew are LPV capable, the decision altitude of 856' would be used.
• If the aircraft and crew are LNAV/VNAV capable, the decision altitude of 1125' would be used.
• If the aircraft or crew were not VNAV capable, a DDA could be calculated (1060 + 60 = 1120' for an aircraft with a 60' pad), and the approach flown using CDFA techniques.

MDA Published with VDA — KASH NDB Rwy 14

Without C073 authorization, crews would have an MDA of 880' with a local altimeter setting, 920' without. They could elect to calculate a DDA and fly the approach using CDFA techniques. (A G450 would use 940' with the local altimeter setting, 980' without.)

"Only Authorized Operators" Approaches

With C073 authorization (OpSpec, MSpec, or LOA), crews can fly this approach using CDFA techniques down to the published MDA's, using them as DA's. (An authorized G450 would use 880' as a DA with the local altimeter setting, 920' without.)

More about this: Vertical Navigation (VNAV).

CDFA Not Advisable due to Obstacles — PHTO RNAV(GPS) Rwy 21

There are at least three clues on the approach plate telling you a CDFA is not advisable:

1. There is no dotted gray line to the runway, which would indicate a vertical descent angle.
2. There is no glide path feather, which would indicate the VNAV glide slope portion of a LNAV/VNAV approach.
3. There is a warning in the profile view: "Descent angle (VNAV) not authorized.

Of course this begs the question: why?

Looking at the airfield diagram we see three obstacles within a mile of the approach end of the runway that will required visual maneuvering at the last moment.

CDFA Not Advisable due to Excessive Descent Rate — KASE Loc DME-E

The approach contains the dotted gray line with a vertical descent angle given, 6.59°. The FAA version also has the requisite VDA depicted. Technically, you have what you need to fly this approach using a constant descent final approach, but it would be unwise. AC 120-108 suggests 3.77° is the maximum for a Category C aircraft.

There are many problems with such and approach, to name just a few:

• Few aircraft can descend at such a steep angle and not accelerate, even when fully configured.
• The normal, flight tested, go around maneuver may not account for such an extreme change in flight path vector.
• If you manage to make it to the runway on speed, you may not have the energy required to flare from this angle.

The CDFA is meant to give you an unchanging flight path, laterally and vertically, from the final approach fix to the runway. Approaches like this are meant for low altitude maneuvering, making them unsuitable for CDFA techniques.

Advisory Circular 120-108, Continuous Descent Final Approach, 1/20/11, U.S. Department of Transportation

EASA Air Ops Annex 1 to VIII, European Aviation Safety Agency, October 2019

FAA-H-8083-15B, Instrument Flying Handbook, U.S. Department of Transportation, Flight Standards Service, 2012

FAA-H-8261-1A, Instrument Procedures Handbook, U.S. Department of Transportation, Flight Standards Branch, 2007

ICAO Doc 8168 - Aircraft Operations - Vol I - Flight Procedures, Procedures for Air Navigation Services, International Civil Aviation Organization, Sixth Edition, 2018

Gulfstream G450 Airplane Flight Manual, Revision 35, April 18, 2013

Jeppesen Airways Manual

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