U.
S. Department of Transportation Federal Aviation Administration Advisory Circular Subject: Continuous Descent Final Approach Date: 3/22/23 AC No: 120-108A Initiated by: AFS-400 Change:
This advisory circular (AC) provides recommendations for operators using a continuous descent final approach (CDFA) technique while conducting a Nonprecision Approach (NPA) instrument approach procedure (IAP). The contents of this document do not have the force and effect of law and are not meant to bind the public in any way, and the document is intended only to provide information to the public regarding existing requirements under the law or agency policies.
We sley L. Mooty Acting Deputy Executive Director, Flight Standards Service
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CONTENTS Paragraph Page
Chapter 1. General1-1
1.1 Purpose of This Advisory Circular (AC)1-1
1.2 Audience1-1
1.3 Where You Can Find This AC1-1
1.4 What This AC Cancels1-1
1.5 Related 14 CFR Regulations1-1
1.6 Related Reading Material (current editions)1-1
1.7 AC Feedback Form1-2
Chapter 2. Background2-1
2.1 NPAs2-1
2.2 Stabilized Approaches2-1
2.3 Approach Designs and Continuous Descent2-1
2.4 Definition of CDFA2-2
2.5 Advantages of CDFA2-2
2.6 Approved NPAs2-2
Chapter 3. Oper ational Procedures and Flight Techniques3-1
3.1 Equipment Requirements3-1
3.2 Approach Requirements3-1
3.3 VDA Design3-3
3.4 Rate of Descent Discussion3-3
3.5 Calculating a Descent Point for a Step-Down Fix Associated with a VDA
Published Between the Step-Down Fix and Runway3-7
3.6 Timing-Dependent Approaches3-9
3.7 Derived DA (DDA)3-9
3.8 Decision Approaching MDA3-9
3.9 Executing a Missed Approach Prior to MAP3-10
3.10 Approaches With a VDP3-10
3.11 Quick-Reference Aircraft Height, Distance, and Rate of Descent Techniques3-11
Chapter 4. Flightcrew Training4-1
4.1 Use of CDFA4-1
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4.2 Manuals and SOPs4-1
4.3 Training4-1
4.4 Training Program Topics4-1
Li st of Figures
Figure 3-1. Instrument Approach Procedures Legend3-2
Figure 3- 2. Climb/Descent Table (Not for Navigation)3-5
Figure 3- 3. Sample Approach Localizer/Non-Directional Beacon La Porte Muni
Runway 2 (Not for Navigation)3-6
Figure 3- 4. Instrument Approach Procedures With Controlling Step- Down Fix
(Not for Navigation)3-7
Figure 3- 5. Approach Example Using Continuous Descent Final Approach3-9
Figure 3- 6. Approach Example Without Using Continuous Descent Final Approach3-10
Lis t of Tables
Table 3-1. Maximum VDAs3-3
1-1 CHAPTER 1. GENERAL
1.1 Purpose of This Advisory Circular (AC). This AC describes how to use a continuous descent final approach (CDFA) technique on a Nonprecision Approach (NPA), as well as recommended general procedures and training guidelines for implementing CDFA as a standard operating procedure (SOP). The contents of this document do not have the force and effect of law and are not meant to bind the public in any way, and the document is intended only to provide information to the public regarding existing requirements under the law or agency policies.
1.2 Audience. The information in this AC applies to all operators conducting CDFA operations under Title 14 of the Code of Federal Regulations (14 CFR) parts 91, 91 subpart K (part 91K), 121, 125, and 135 within the U.S. National Airspace System (NAS).
1.3 W here You Can Find This AC. You can find this AC on the Federal Aviation Administration’s (FAA) website at https://www.faa.gov/regulations_policies/advisory_cir culars and the Dynamic Regulatory System (DRS) at https://drs.faa.gov.
1.4 What This AC Cancels. AC 120-108, Continuous Descent Final Approach, dated January 20, 2011, is canceled.
1.5 Related 14 CFR Regulations.
• Part 91, General O perating and Flight Rules.
• Part 97, Standard Instrument Procedures.
• Part 119, Certif ication: Air Carriers and Commercial Operators.
• Part 121, Operating Requirements: Domestic, Flag, a nd Supplemental Operations.
• Part 125, Certification and Operations: Airplanes Having a Seating Capacity of 20 or More Passengers or a Maximum Payload Capacity of 6,000 Pounds or More; and Rules Governing Persons On Board Such Aircraft.
• P art 135, Operating Requirements: Commuter and On Demand Operations and Rules Governing Persons On Board Such Aircraft.
1.6 R elated Reading Material (current editions) . The majority of the document references in this AC are from the most current version as designated by parentheses ( ) placed at the end of the document title. In some cases, a letter will indicate the actual version.
1.6.1 F AA ACs and Aviation Handbooks and Manuals . The following are the latest ACs and/or aviation handbooks and manuals:
• AC 91-79( ) , Mitigat ing the Risks of a Runway Overrun Upon Landing.
• FAA Aeronautical Information Manual (AIM).
• FAA Instrument Procedures Handbook (FAA-H-8083-16B).
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1.6.2 Orders.
• FAA Order 8260.3( ), United States Standard for Terminal Instrument Procedures (TERPS).
• FAA Order 8260.19( ), Flight Procedures and Airspace.
1.7 AC Feedback Form. For your convenience, the AC Feedback Form is the last page of this AC. Note any deficiencies found, clarifications needed, or suggested improvements regarding the contents of this AC on the Feedback Form.
2-1 CHAPTER 2. BACKGROUND
2.1 NPAs. Current NPAs are designed with and without step-down fixes in the Final Approach Segment (FAS). NPAs designed without step-down fixes in the FAS allow for an immediate descent to the minimum descent altitude (MDA) after crossing the final approach fix (FAF). The aircraft remains at the MDA until it descends for the runway or reaches the missed approach point (MAP). This technique is described as the “dive and drive.” NPAs with step-down fix altitudes in the FAS do not allow an immediate descent to the MDA; they require additional pitch and power changes during the vertical descent to the MDA in order to cross at or above the step-down fix altitude. Once the aircraft reaches the MDA, it again remains at the MDA until it descends for the runway or reaches the MAP. In both scenarios, NPAs flown without a constant descent require multiple thrust, pitch, and altitude adjustments inside the FAF. These adjustments increase pilot workload and potential errors during a critical phase of flight. The dive and drive technique also results in the aircraft maintaining an extended level flightpath as low as 250 feet (ft) above the ground in instrument meteorological conditions (IMC). This technique could result in an unsafe final Vertical Path (VPATH) to the runway. This AC describes how to conduct more stabilized approaches.
2.2 Stabilized Approaches. A stabilized approach is a key feature to a safe approach and landing. Operators are encouraged to use the stabilized approach concept (refer to AC 91-79( )) to help eliminate controlled flights into terrain (CFIT). AC 91-79( ) describes a profile that has an aircraft stabilized before descending through a 1,000 ft window in IMC, or through a 500 ft above touchdown zone elevation (TDZE) window in visual meteorological conditions (VMC) to the landing touchdown point. This profile is characterized by maintaining a stable approach speed, constant descent rate, constant vertical Flight Path Angle (FPA), and the same aircraft configuration. This AC will focus on techniques to fly a stabilized vertical descent from the FAF to the landing touchdown point. It assumes the aircraft is in final configuration approaching the FAF and that the descent profile will adhere to the stabilized approach concept referenced in AC 91-79( ).
2.3 Approach Designs and Continuous Descent. A precision instrument approach procedure (IAP) (e.g., instrument landing system (ILS) and Ground Based Augmentation System (GBAS) Landing System (GLS)) and some NPA Area Navigation (RNAV) Global Positioning System (GPS) approach procedures with vertical guidance (APV)
(e.g., lateral navigation (LNAV)/vertical navigation (VNAV) and localizer performance with vertical guidance (LPV)) have a continuous descent approach profile in their design.
Conventional NPAs (e.g., Localizer (LOC) only and very high frequency (VHF) omni-directional range (VOR)) and NPA RNAV approaches (e.g., LNAV and Localizer Performance (LP)) are not designed with a vertical flightpath. RNAV approaches without approved vertical guidance and conventional NPAs should be flown, whenever possible, using a CDFA technique. Flying NPAs with a continuous descent profile can provide a safety advantage over flying approaches using the dive and drive technique. Therefore, the goal of using a CDFA on an NPA is to incorporate the safety benefits from flying a stabilized continuous descent as a standard practice.
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2.4 Definition of CDFA. CDFA is a technique for flying the FAS of a NPA as a continuous descent. The technique is consistent with stabilized approach procedures and has no level off. A CDFA starts from an altitude/height at or above the FAF and proceeds to an altitude/height approximately 50 ft (15 meters) above the landing runway threshold or to a point where the type of aircraft will begin the flare maneuver.
2.5 Advantages of CDFA. The following is a list of benefits that operators may realize when using a CDFA technique versus not using it:
• Increased safety by employing the concepts of stabilized approach criteria and procedure standardization.
• Improved pilot situational awareness (SA) and reduced pilot workload.
• Improved fuel efficiency by minimizing the low-altitude level flight time.
• Reduced noise level by minimizing the level flight time at high-thrust settings.
• Procedural similarities to APV and precision approach operations.
• Reduced probability of infringement on required obstacle clearance during the FAS.
2.6 Approved NPAs. The FAA recommends accomplishing a CDFA on all of the following published NPAs:
• VOR;
• VHF omni-directional range station/distance measuring equipment (VOR/DME);
• Non-directional radio beacon (NDB);
• NDB/DME;
• LOC, Localizer back course (LOC BC);
• LOC/DME;
• Localizer type directional aid (LDA);
• LDA/DME;
• Simplified Directional Facility (SDF);
• SDF/DME;
• RNAV (GPS) LNAV line-of-minima;
• RNAV (GPS) LP line-of-minima; and
• Tactical Air Navigation System (TACAN).
3-1 CHAPTER 3. OPERATIONAL PROCEDURES AND FLIGHT TECHNIQUES
3.1 Equipment Requirements. A CDFA does not require specific aircraft equipment;
however, the aircraft must be equipped to accomplish the NPA procedure. Pilots can safely fly NPAs with a CDFA using basic piloting techniques, aircraft flight management systems (FMS), or RNAV systems. Pilots can use points defined by a DME fix, crossing radial, GPS distance from the runway, etc., on the approach plate to track their progress along both the lateral and vertical approach paths to the MAP.
3.2 Approach Requirements. A CDFA may be flown on any NPA. There are no specific approach requirements nor any requirement for a vertical descent angle (VDA), glide path (GP), or visual descent point (VDP) to be published on an IAP in order to fly a CDFA. However, the use of a published VDA or a GP with a published or derived VDP on the IAP can help pilots calculate a desired rate of descent. This rate of descent may be flown by using the aircraft’s Vertical Velocity Indicator (VVI). A VDA provides FAS advisory vertical information only. A GP provides approved vertical guidance for the FAS. The Terminal Procedures Publication (TPP) IAP Legend (see Figure 3-1, Instrument Approach Procedures Legend) defines both the VDA and GP. Conventional NPAs or RNAV approaches with LNAV- or LP-only minima may or may not be published with a VDA. RNAV approaches with a published decision altitude (DA)
(e.g., those with LNAV/VNAV or LPV minima) depict a GP angle. A GLS procedure is also published with a DA and a GP. Aircraft with FMS, barometric vertical navigation (baro-VNAV), Satellite-Based Augmentation System (SBAS) (implemented in the United States as wide area augmentation system (WAAS)), or similar equipment may provide the published VDA or GP when the IAP is selected from the database. Aircraft equipped with FPA allows the pilot to enter an electronic descent angle based on the published VDA or GP. Pilots flying aircraft without either type of equipment should manually compute a required rate of descent for accomplishing the CDFA.
Figure 3-1. Instrument Approach Procedures Legend 15120
LEGEND INSTRUMENT APPROACH PROCEDURES (CHARTS)
PROFILE VIEW
2. "GP" on GLS and RNAV procedures indicates that either electronic vertical guidance (via Wide Area Augmentatior System - WAAS or Ground Based Augmentation System - GBAS) or barometric vertical guidance is provided. GLS and RNAV procedures with a published decision altitude (DA/H) depict a GP angle and TCH in the following format: GP 3.00°
3. An advisory vertical descent angle (VDA) is provided on non-vertically guided conventional procedures and RNAV procedures with only a minimum descent altitude (MDA) to assist in preventing controlled flight into terrain. On Civil (FAA) procedures, this information is placed above or below the procedure track following the fix it is based on.
Absence of a VDA or a note that the VDA is not authorized indicates that the prescribed obstacle clearance surface is not clear and the VDA must not be used below MDA. VDA is depicted in the following format: TCH S5" LOM - Procedure Turn (PT) Fix ILS or LOC APPROACH - PT Fix Altitude until Established Outbound 4000- (Some approaches may use a restrictive note) *307° 2156 - Glide Slope Ahitude at Outer Marker/FAF - FAF (precision approaches) PT Completion -FAF (non-precision approaches) Altitude - 2400 127 ILS • Missed Approach Point Glide Slope - → GS 3.00° -Glide Slope - Missed Approach Track Threshold Crossing Height- → TCH 55 ,2400 Glide Slope Intercept Altitude Airport Profile RNAV and GLS PROCEDURES WITH VERTICAL GUIDANCE 7 NM VGSI and RNAV glidepath not coincident Holding Pattern BAXKU IPHIB (VGSI Angle 3.00/TCH 23).
8100723° -303° ARUJU WUGOD * INAV only
- 123°- 7000 5700 4 NM to •1.6 NM to RW12 RW12 Glidepoth * GP 3.00° TCH 38 5700 *4480 Visual Descent Point (VDP) Visual segment below MDA/DA is clear of obstacles on 34:1 slope (Absence of shaded area indicates 34:1 is not clear.)
NON-VERTICALLY GUIDED CONVENTIONAL PROCEDURES AND
RNAV PROCEDURES WITH MDA ONLY ABC Vertical Descent ABC VOR Angle (VDA) VOR Crossing height Threshold TCH 50 2.93 3.3) - 313° *313° 133→3000 ABC VOR 5.8) 2400 Holding Pattern One Minute + 2,5 NM 133 NM
DESCENT FROM HOLDING PATTERN ABC VOR 133°- 313° -3000 *2400
ALTITUDES PROFILE SYMBOLS 5500 Mandatory Alritude 3000 Recommended Alitude > Visual Flight Path 2500 Minimum Altitude 5000 Mandatory Block 3000 Altitude 2400 Note: Facilities and waypoint are depicted as a solid vertica 4300 Maximum Altitude Visual Descent Point (VDP) line while fixes and intersections are depicted as a dashed vertical line LEGEND Note: Use the "Legends & General Information (PDF)" hyperlink at the bottom of the following Terminal Procedures web page to view current legend information: https://www.faa.gov/air_traffic/flight_info/aeronav/digital_products/ dtpp/search/.
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3.3 VDA Des ign. A VDA is calculated from the FAF altitude to the threshold crossing height (TCH) altitude. It is published on the IAP with the VDA symbol . The optimum VDA is 3.0°. The minimum VDA is 2.75°. Table 3-1 below provides the maximum VDAs for different aircraft categories. In some cases, the VDA is calculated from a step-down fix altitude to the TCH instead of the FAF altitude to the TCH.
Tabl e 3-1. Maximum VDAs *Un ited States Air Force (USAF)/United States Navy (USN) Category (CAT) E maximum is 3.5°.
3.3.1 VDA Based o n Step-Down Fix. On approaches with step-down fixes, the goal is to publish a VDA that keeps the VPATH above the step-down fix altitude. However, in some cases the VDA is calculated from the step-down fix altitude to the TCH. In this situation, the VDA symbol is published on the IAP following the associated step-down fix (see Figure 3-4, Instrument Approach Procedures With Con trolling Step-Down Fix (Not for Navigation)). In this example, using an obsolete approach procedure at Tallahassee Regional (now Tallahassee International), the 2.98° VDA is applicable from waypoint WAPIM to a TCH of 46 ft. Paragraph 3.5.3 below will demonstrate how to calculate descent rates for this type of example. In most of these cases, the descent angle between the FAF altitude and the step-down fix altitude is slightly shallower than the published VDA for the segment between the step-down fix and the runway.
Note: Third-par ty designed IAPs may depict this type of approach in a different format.
3.3.2 NPA Without a Published VDA. When an approach is publ ished without a VDA, Flight Inspection Services (FIS) has previously determined that a VDA should not be published due to obstacles. Flying the VDA below the MDA might not provide acceptable obstacle clearance. The VDA will not be published and a chart profile note reading “Visual Segment – Obstacles” should be published on the TPP IAP. Operators may still calculate and fly a CDFA to the runway, but, if doing so, must not descend below the MDA without visual requirements (refer to part 91, § 91.175). Once passing the MDA into the visual segment of the IAP, operators must see and avoid all obstacles.
3.4 Rate of Desce nt Discussion. U.S. Government and private flight information publications offer a pilot a way to compute a rate of descent in feet per minute (fpm) from a descent angle (degrees) and/or a descent gradient (feet per nautical mile (NM) (ft/NM)). (See Figure 3-2, Climb/Descent Table (Not f or Navigation).) Pilots may use a
3-4 published VDA or GP in the chart to get a ft/NM descent gradient or a fpm descent rate.
Pilots may also calculate a rate of descent without a VDA or GP to accomplish a CDFA.
This is accomplished by:
1. Calculating a descent gradient by subtracting the TDZE from the FAF altitude, minus 50 ft and then dividing by the distance from the FAF to runway, published in NM;
and then
2. Turning the descent gradient into a rate of descent from the Climb/Descent table.
Note: In both scenarios, the calculated fpm descent rate may be flown using the aircraft’s VVI.
3.4.1 Descent Gradient and Rate of Descent Calculation. See Figure 3-3, Sample Approach:
Localizer/Non-Directional Beacon La Porte Muni Runway 2 (Not for Navigation). In this example the climb/descent table, aircraft groundspeed (GS), and a published VDA are used to determine the descent gradient and rate of descent/VVI needed to fly a CDFA on the LOC/NDB Runway 2 approach at La Porte Municipal Airport.
3.4.1.1 VDA. Fi nd the published VDA on Figure 3-3. In this example, it is 3.20°.
3.4.1.2 How to Calculate a Descent Gradient for a Published VDA. Find the descent gradient that equates to a VDA of 3.20° (see Figure 3-2, column 1). In this example, 3.2° equates to 340 ft/NM found in column 2, same row.
3.4.1.3 How to Calculate a Descent Rate for a Given GS. Find the descent rate based on GS (see Figure 3-2). Find the column with a GS of 120 knots (kts).
Move down the column until it intersects the row with 3.2°/340 ft/NM. The two intersect at 680; so a 680 fpm rate of descent is required to fly the
3.20° descent angle at 120 kts.
Figure 3-2. Climb/Descent Table (Not for Navigation) CLIMB/DESCENT TABLE 10042
INSTRUMENT TAKEOFF OR APPROACH PROCEDURE CHARTS
RATE OF CLIMB/DESCENT TABLE A rate of climb/descent table is provided for use in planning and executing climbs or descents under known or approximate ground speed conditions. It will be especially useful for approaches when the localizer only is used for course guidance. A best speed, power, altitude combination can be programmed which will result in a stable glide rate and altitude favorable for executing a landing if minimums exist upon breakout. Care should always be exercised so that minimum descent altitude and missed approach point are not exceeded.
CLMB/ DESCENT ANGLE f/NM GROUND SPEED (knots) (degrees and tenths) 60 90 120 150 180 210 240 270 300 330 360
2.0 210 210 320 425 530 635 743 850 955 1060 1165 1275
2.5 265 265 400 530 665 795 930 1060 1195 1325 1460 1590
2.7 287 287 430 574 717 860 1003 1147 1290 1433 1576 1720
2.8 297 297 446 595 743 892 1041 1189 1338 1486 1635 1783
2.9 308 308 462 616 770 924 1078 1232 1386 1539 1693 1847
3.0 318 318 478 637 797 956 1115 1274 1433 1593 1752 1911
3.1 329 329 494 659 823 988 1152 1317 1481 1646 1810 1975 H
3.2 340 340 510 680 850 1020 1189 1359 1529 1699 1869 2039 IZU 3.3 350 350 526 701 876 1052 1227 1402 1577 1752 1927 2103
3.4 361 361 542 722 903 1083 1264 1444 1625 1805 1986 2166
3.5 370 370 555 745 930 1115 1300 1485 1670 1860 2045 2230
4.0 425 425 640 850 1065 1275 1490 1700 1915 2125 2340 2550
4.5 480 480 715 955 1195 1435 1675 1915 2150 2390 2630 2870
5.0 530 530 795 1065 1330 1595 1860 2125 2390 2660 2925 3190
5.5 585 585 880 1170 1465 1755 2050 2340 2635 2925 3220 3510
6.0 640 640 960 1275 1595 1915 2235 2555 2875 3195 3510 3830
6.5 690 690 1040 1385 1730 2075 2425 2770 3115 3460 3805 4155
7.0 745 745 1120 1490 1865 2240 2610 2985 3355 3730 4105 4475
7.5 800 800 1200 1600 2000 2400 2800 3200 3600 4000 4400 4800
8.0 855 855 1280 1710 2135 2560 2990 3415 3845 4270 4695 5125
8.5 910 910 1360 1815 2270 2725 3180 3630 4085 4540 4995 5450
9.0 960 960 1445 1925 2405 2885 3370 3850 4330 4810 5295 5775
9.5 1015 1015 1525 2035 2540 3050 3560 4065 4575 5085 5590 6100
10.0 1070 1070 1605 2145 2680 3215 3750 4285 4820 5355 5890 6430 CLIMB/DESCENT TABLE 10042 3-5