# AC 120-108A: Continuous Descent Final Approach - Type: Advisory circular (guidance, not mandatory unless a rule or AD requires it) - Status: Current - Approved: March 22, 2023 - Last reviewed: August 27, 2024 - Family: AC 120-108 - Cancels: [AC 120-108](https://openairdocs.org/ac/120-108) - 14 CFR parts: 91, 97, 119, 121, 125, 135 - 14 CFR sections: [91.175](https://www.ecfr.gov/current/title-14/section-91.175) - Pages: 22 - PDF: https://openairdocs.org/files/sha256/8a/0c/8a0ce31f3ad985b88b003716e7f1cb6e856e0f17deed7bbca1f56b2f8d48e27a - FAA DRS: https://drs.faa.gov/browse/excelExternalWindow/DRSDOCID161241029920230324153308.0001 - DRS record last changed: November 22, 2025 - Page: https://openairdocs.org/ac/120-108 ## Versions - [AC 120-108A](https://openairdocs.org/ac/120-108) (Current), approved Mar 22, 2023, 22 pages - [AC 120-108](https://openairdocs.org/ac/120-108?v=B335ECB9E52E0316862578290071C32D) (Historical), approved Jan 20, 2011, 14 pages ## Text Each page's text from the PDF; open the PDF at a page with #page=N. Some pages are OCR from the scanned FAA advisory circular. OCR can misread letters and numbers. Those pages are marked (OCR). ### Page 1 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 ### Page 2 ii CONTENTS Paragraph Page Chapter 1. General … 1-1 1.1 Purpose of This Advisory Circular (AC) … 1-1 1.2 Audience … 1-1 1.3 Where You Can Find This AC … 1-1 1.4 What This AC Cancels … 1-1 1.5 Related 14 CFR Regulations … 1-1 1.6 Related Reading Material (current editions) … 1-1 1.7 AC Feedback Form … 1-2 Chapter 2. Background … 2-1 2.1 NPAs … 2-1 2.2 Stabilized Approaches … 2-1 2.3 Approach Designs and Continuous Descent … 2-1 2.4 Definition of CDFA … 2-2 2.5 Advantages of CDFA … 2-2 2.6 Approved NPAs … 2-2 Chapter 3. Oper ational Procedures and Flight Techniques … 3-1 3.1 Equipment Requirements … 3-1 3.2 Approach Requirements … 3-1 3.3 VDA Design … 3-3 3.4 Rate of Descent Discussion … 3-3 3.5 Calculating a Descent Point for a Step-Down Fix Associated with a VDA Published Between the Step-Down Fix and Runway … 3-7 3.6 Timing-Dependent Approaches … 3-9 3.7 Derived DA (DDA) … 3-9 3.8 Decision Approaching MDA … 3-9 3.9 Executing a Missed Approach Prior to MAP … 3-10 3.10 Approaches With a VDP … 3-10 3.11 Quick-Reference Aircraft Height, Distance, and Rate of Descent Techniques … 3-11 Chapter 4. Flightcrew Training … 4-1 4.1 Use of CDFA … 4-1 ### Page 3 iii 4.2 Manuals and SOPs … 4-1 4.3 Training … 4-1 4.4 Training Program Topics … 4-1 Li st of Figures Figure 3-1. Instrument Approach Procedures Legend … 3-2 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 Approach … 3-9 Figure 3- 6. Approach Example Without Using Continuous Descent Final Approach … 3-10 Lis t of Tables Table 3-1. Maximum VDAs … 3-3 ### Page 4 **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). ### Page 5 1-2 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. ### Page 6 **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. ### Page 7 2-2 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). ### Page 8 **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. ### Page 9 (OCR) 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/. 3-2 ### Page 10 3-3 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 ### Page 11 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. ### Page 12 (OCR) 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 ### Page 13 (OCR) Figure 3-3. Sample Approach Localizer/Non-Directional Beacon La Porte Muni Runway 2 (Not for Navigation) LA PORTE, INDIANA AL-6248 (FAA) 15316 LOC I-PPO APP CRS Rwy Idg TDZE 5000 805 LOC/NDB RWY 2 110.95 023° Apt Elev 812 LA PORTE MUNI (PPO) A NA When local altimeter setting not received, use South Bend altimeter setting and increase all MDA 60 feet; increase S-2 Cat D visibility ¼ mile. Helicopter visibility reduction below ¾ SM not authorized 2300 then climbing right turn to MISSED APPROACH: Climb to 2500 direct OXI VOR/DME and hold. AWOS-3 SOUTH BEND APP CON * UNICOM 119.825 132.05 257.8 123.0 (CTAF) • LOCALIZER 110.95 1021A 41109 APPO : EA 1209‡ 1954 1320A JAF **LA PORTE 356 NUL II-..** **KNOX** 115.6 OX == Chan 103 MISA IUL 25 NA ELEV 812 TDZE 805 3000 EIL Rwys 2, 14, 20 and 32 0 AIRL Rwys 2-20 and 14-32€ 2300 2500 OXI Remain • within 10 NM • 203° from FAF VGSI and descent angles not coincident 2300 - • 023°• 2300* 3.20° -023° (VGSI Angle 3.00/TCH 24). TCH 45 • 4.3 NM FAF to MAP 4.3 NM CATEGORY S-2 1220-1 415(50-1) 1220-1¼ 415(500-1¼) Knots 60 90 120 150 180 1320-1½ 1380-2 Min:Sec 4:18 2:52 2:09 1:43 1:26 CIRCLING 1320-1 508(600-1) 508(600-1½) 568(600-2 LA PORTE, INDIANA LA PORTE MUNI (PPO) Amdt 1D 08JAN15 41°34'N-86°44"W LOC/NDB RWY 2 3-6 ### Page 14 (OCR) 3.5 Calculating a Descent Point for a Step-Down Fix Associated with a VDA Published Between the Step-Down Fix and Runway. When the charted VDA is between the step-down fix and the runway, beginning a normal CDFA descent at the FAF may result in the aircraft crossing the step-down fix below the minimum allowable altitude. To prevent this, pilots may use one of two methods to fly this type of approach. The two methods are a descent at the FAF and a descent past the FAF. 3.5.1 Descent at the FAF. When a descent begins at the FAF, descend from the FAF at a rate of descent to cross at or above the step-down fix altitude. When the aircraft reaches the step-down fix, transition to the published VDA rate of descent. In this scenario, the rate of descent from the FAF to the step-down fix will tend to be shallower than the rate of descent from the step-down to the runway. (See paragraph 3.5.3.1.) 3.5.2 Descent Past the FAF. Begin a descent at a point past the FAF that will allow the aircraft to descend at the published VDA rate of descent for the entire FAS and cross at or above the step-down fix altitude. (See paragraph 3.5.3.2.) 3.5.3 Demonstration of Descent Techniques. Both techniques are demonstrated using an example based on an obsolete approach at Tallahassee Regional (now Tallahassee International) VOR RWY 18 approach (see Figure 3-4). Figure 3-4. Instrument Approach Procedures With Controlling Step-Down Fix (Not for Navigation) Rwy Idg 6076 TDZE 81 Apt Elev 81 Remain VORTAC 1600 within 10 NM • 353° WAPIM SZW 6.7 379 RADAR 2000 • 173°- 2000 -173°- SZW 8.7 760 2.98 TCH 46 6.7 NM - 2 NM CATEGORY A D S-18 760-1 679(700-1) 760-2 760-2¼ 679(700-2) 679(700-2¼) CIRCLING 760-1 679(700-1) 760-2 760-2¼ 679(700-2) 679 (700-2¼) WAPIM FIX MINIMUMS 540-1¼ 540-1½ S-18 540-1 459(500-1) 459 (500-1¼) 459 (500-1½) 580-1½ 640-2 CIRCLING 540-1 459(500-1) 499 (500-1½½) 559(600-2) TALLAHASSEE, FLORIDA TALLAHASSEE RGNL (TLH) Amdt 11A 09043 VOR RWY 18 3-7 ### Page 15 3-8 3.5.3.1 Calculate the Descent Rates for Step-Down Fix from FAF. In this example, the descent angle from the FAF to the step-down fix is abnormally shallow compared to the published VDA. 1. Find the D escen t Gradient/Descent Angle from the FAF to Step-Down Fix. Take the FAF altitude (2,000 ft) and subtract the step-down fix altitude (760 ft) to get 1,240 ft. FAF (2,000 ft) – 760 ft = 1,240 ft 2. Descent Gradient from the FAF to Step- Down Fix. Take 1,240 ft and divide by the distance between the FAF and step-down fix (6.7 NM). 1,240 ft / 6.7 NM = 185 ft/NM The de scent gradient calculated is 185 ft/NM, which translates to a descent angle of less than 2.0° from the climb/descent table (see Figure 3-2). Although the chart does not have values for less than a 2.0° angle, a rate of descent can still be calculated for 120 kts, or 2 miles per minute. 3. Descent Rate from the FAF to Step-Down Fix. Take 185 ft/NM and multiply by 2 miles per minute and the rate of descent is 370 fpm. 185 ft/NM × 2 miles per minute = 370 fpm Mai ntain the 370 fpm rate of descent until reaching the step-down fix. This should place the aircraft at the step-down fix altitude of 760 ft. At the 760 ft step-down fix, transition to a descent rate commensurate with the published 2.98° VDA. The climb/descent table (see Figure 3-2) shows that 2.98° equates to a descent gradient of 316 ft/NM or a rate of descent of 632 fpm at 120 kts. 3.5.3.2 Calculate the Descent Point Beyond the FAF to Meet Step-Down Fix Altitude. This example shows how to calculate a descent point beyond the FAF, which allows a single rate of descent commensurate with the VDA from the descent point to the runway, while placing the aircraft at or above the step-down fix. 1. Find D esi red Altitude to Lose. Take the FAF altitude, subtract the TDZE, and subtract the published TCH if available. If the TCH is not available, use 50 ft. This gives you desired altitude to lose in order to be at threshold at the TCH. FAF (2,000 ft) – TDZE (81 ft) – TCH (46 ft) = 1,873 ft 2. Find D istance from R unway to Descent Point. Take the desired altitude to lose (1,873 ft) and divide by the descent gradient 316 ft/NM or a 2.98° VDA. 1,873 ft / 316 ft/NM= 5.9 NM ### Page 16 3-9 This distance is 5.9 NM from the runway threshold or 2.8 DME from the SZW Collocated VOR and TACAN (VORTAC). 8.7 NM – 5.9 NM = 2.8 NM A descent from 2,000 ft beginning at 5.9 NM from the runway or 2.8 DME from SZW will allow the aircraft to descend at a 2.98° VDA or a descent rate of 632 fpm at 120 kts. The aircraft should cross the step-down fix at or above 760 ft and the threshold at 46 ft. Note: During any approach, pilots must use a vertical FPA that meets all IAP altitude restrictions in order to maintain obstacle and/or terrain clearance. Pilots should use the aircraft barometric altimeter to meet all altitude restrictions. 3.6 Timing-Dependent Approaches. Control of airspeed and rate of descent is particularly important on approaches dependent on timing to identify the MAP. Pilots should cross the FAF at the final approach speed and be configured for landing. 3.7 Derived DA (DDA). Pilots must not descend below the MDA when executing a missed approach from a CDFA. Pilots must initiate a go-around at an altitude above the MDA (sometimes referred to as a DDA) to ensure the aircraft does not descend below the published MDA. (Refer to § 91.175.) 3.8 Decision Approaching MDA. Flying the published VDA will have the aircraft intersect the MDA at a point before the MAP. Approaching the MDA, the pilot has two choices: continue the descent to land with required visual references, or execute a missed approach, not allowing the aircraft to descend below the MDA. (See Figure 3-5 below.) Figure 3-5. Approach Example Using Continuous Descent Final Approach 3.8.1 CDFA Visual Example. In this situation, flying a CDFA that equates to a VDA or GP of 3° from the FAF will result in reaching the DDA and/or MDA prior to the published MAP. The pilot has two courses of action to take at the DDA: ### Page 17 3-10 1. Point (1). If § 91.175 required visual cues are acquired, continue visually to the landing runway while maintaining clear of obstacles. 2. Point (2). If § 91.175 required visual cues are not acquired, execute a missed approach procedure. Begin a missed approach at the DDA. Do not descend below the MDA. Proceed on track to the MAP before accomplishing a turn. 3.9 Executing a Missed Approach Prior to MAP. When executing a missed approach prior to the MAP and not cleared for an air traffic control (ATC) climbout instruction, fly the published missed approach procedure. Proceed on track to the MAP before accomplishing a turn. 3.10 Approaches With a VDP. A VDP (see Figure 3-6 below) is shown by a bold letter “V” positioned above the procedure track. The VDP is a defined point on the final approach course of a nonprecision straight-in approach procedure from which a normal descent from the MDA to the runway touchdown point may be commenced. Flying the published VDA on an approach constructed with a VDP should have the aircraft cross the MDA at or beyond the VDP. In this example, the dotted lines will not be found on an actual approach plate; the lines are provided to give a visual representation of the MDA and MAP. Figure 3-6. Approach Example Without Using Continuous Descent Final Approach 3.10.1 Approach Without CDFA (Dive and Drive). This example explains what may happen when using the dive and drive technique and when a descent from the MDA is not accomplished at the published or pilot-computed VDP (3.0°). In both scenarios, the aircraft descended immediately from the FAF to the MDA at a greater than 3.0° descent angle. This maneuver requires multiple thrust, pitch, and altitude adjustments. The pilot levels off at the MDA of 300 ft and continues level flight until reaching the VDP, where, if the visual requirement to continue the approach is met, a descent should begin to the runway at a 3.0° FPA. The VDP will be located approximately 1 NM from the runway with an MDA altitude of 300 ft. See Figure 3-2 to compute rates of descent. 3.10.2 Point A—Descent Before VDP. If the pilot descends .5 NM before the VDP (see Figure 3-6, point A), a 2.0° descent angle is required from the MDA to the TCH. This corresponds to an approximate 425 fpm rate of descent at 120 kts. This low rate of ### Page 18 3-11 descent requires a higher power setting and an increased deck angle. The aircraft is closer to the ground for a longer period and is more susceptible to a higher drag profile, resulting in obstacle and/or terrain clearance loss. 3.10.3 Point B—Descent After VDP. If the pilot descends .5 NM past the VDP (see Figure 3-6, point B), a 6.0° descent angle is required from the MDA to the TCH. This corresponds to an approximate 1,275 fpm rate of descent at 120 kts. This creates a steep final approach with low power settings, which may lead to an unstable approach, a missed approach, and/or an unsafe landing. 3.11 Quick-Ref erence Aircraft Height, Distance, and Rate of Descent Techniques. This paragraph discusses how to determine an aircraft’s height above the ground at a certain distance from the runway and at a desired rate of descent. This will help operators compare where the aircraft should be in regards to a calculated vertical descent for a CDFA in the FAS. Small differences will occur with different FPAs, but the ability to calculate a number and compare against an actual aircraft position is an invaluable tool for SA. 3.11.1 Aircraft Height and Dista nce from Runway. This technique provides a simple and quick way to determine the aircraft altitude on a 3.0° FPA. Pilots should remember the ratio 3:1—the aircraft will descend 300 ft for every 1 NM traveled on a 3.0° FPA. This information can then be used to calculate back from the runway to the aircraft to determine an aircraft altitude at a determined distance from the runway. In this discussion we will use the calculated altitude plus 50 ft in order to harmonize with the CDFA’s definition of flying a constant descent in the FAS until they reach a height of approximately 50 ft (15 meters) above the landing runway threshold (or to a point where the type of aircraft will begin the flare maneuver). Using the 3:1 ratio and counting back from the runway: At 1 NM the aircraft should be at 350 ft ((1 NM × 300 ft) + 50 ft), At 2 NM the aircraft should be at 650 ft ((2 NM × 300 ft) + 50 ft), At 3 NM the aircraft should be at 950 ft ((3 NM × 300 ft) + 50 ft), and so on. These quick calculations can be used in instrument flight rules (IFR) or visual flight rules (VFR) and can be used as a quick reference to compare an expected aircraft position to the actual position on the FAS. 3.11.1.1 Barometric Altimeter. When using the barometric altimeter to monitor these altitudes, the altitude will show 350 ft, 650 ft, and 950 ft (plus the pressure altitude correction for each measurement). For a runway with an airfield elevation of 400 ft, the barometric altimeter should show an approximate altitude of 750 ft (350 ft + 400 ft), 1,050 ft (650 ft + 400 ft), and 1,350 ft (950 ft + 400 ft). 3.11.1.2 Radar Altimeter. The radar altimeter shows the height above the ground. The radar altimeter will show 350 ft, 650 ft, 950 ft, etc. ### Page 19 3-12 3.11.2 Aircraft Target Rate of Descent. T his technique is used to determine a target aircraft’s rate of descent that can be checked/flown with the VVI. This calculation is five times the aircraft GS on an approximate 3° FPA. Using 120 kts GS, the calculation would be 5 × 120 kts GS = 600 fpm. Comparing against Figure 3-2, 120 kts at 3.0° is 637 fpm. Although not an exact number, it provides the operator a way to quickly determine if the aircraft is close to the desired rate of descent on a 3° FPA. 3.11.3 Height, Distance, and R ate of Descent from Runway. When the two techniques are used together: At 1 NM we should s ee a height of 350 ft and a VVI of 600 fpm, At 2 NM we should see a height of 650 ft and a VVI of 600 fpm, and so on. Higher FPAs will result in higher heights above the ground and higher rates of descent at the distances of 1 NM, 2 NM, 3 NM, etc.; while lower FPAs will result in lower heights above the ground and lower rates of descent. ### Page 20 **4-1 CHAPTER 4. FLIGHTCREW TRAINING** 4.1 Use of CDFA. Using a CDFA on a suitable NPA should be an SOP. Operators who use a CDFA technique on NPAs should incorporate CDFA training into their training programs where NPAs are performed and evaluated. This AC does not recommend one technique over another or recommend all techniques be covered in training. Operators may choose and train to a preferred CDFA method. 4.2 Manuals and SOPs. Operators should revise their flight manuals and/or SOPs to identify CDFAs as a standard method of performing an NPA. 4.3 Training. Additional flight training to use the CDFA technique is not required for pilots qualified to conduct NPAs with advisory vertical guidance in accordance with the operator’s certificate. However, operators should provide flightcrews with appropriate ground training before performing CDFA operations. The ground training may be computer-based, published in flight operations bulletins, or provided via other similar means deemed acceptable by the Principal Operations Inspector (POI). Flightcrew members should receive training specific to the aircraft type, the installed flight guidance, and the navigation system, and on how to utilize the system when using the CDFA technique for applicable approach profiles. Part 91 operators should be familiar with CDFA techniques and be proficient with navigation systems they use to perform a CDFA, if applicable. 4.4 Training Program Topics. Each operator’s CDFA training program should address the following topics: 1. Stabilized Approach Concept. Operators should emphasize the stabilized approach concept and the safety benefits of using the CDFA. 2. When Not to Use CDFA. O perators should discuss approach characteristics (e.g., circling-only minima) and environmental factors (e.g., icing) that could make the use of CDFA inadvisable. 3. Baro-VNAV . Operators should discuss the use of the RNP system’s baro-VNAV advisory vertical guidance, if applicable, during NPA operations. 4. SBAS/WAAS. Ope rators should discuss the use of the RNP system’s SBAS-based (e.g., WAAS-based) advisory vertical guidance, if applicable, during NPA operations. 5. Calculating Rate of Descent. Ope rators should discuss methods for translating the published GP or VDA into the required rate of descent for aircraft not equipped with a system capable of computing and flying a vertical profile. 6. Confirming VPATH. Operators should discuss techniques for tracking progress along the final approach vertical profile. 7. M eeting IAP Altitud e Restrictions. Operators should discuss techniques for ensuring compliance with all altitude restrictions in the FAS. ### Page 21 4-2 8. Calculating a DDA . Operators should discuss how to calculate a DDA to ensure the aircraft does not descend below the MDA when accomplishing a missed approach on a CDFA. 9. D ive and Drive Maneuver. Ope rators should discuss the impact on approach stabilization by using the dive and drive technique. (See Figure 3-6.) 10. Crew Coordination. Operators should discuss pilot flying (PF) and pilot monitoring (PM) callouts and other crew coordination activities needed to ensure safe transition from the vertical profile to either landing or a go-around/missed approach at the MDA or DDA. 11. Go-Around Pri or to MAP. Operators should discuss procedures for executing a go-around prior to reaching the MAP. 12. Visual Glide Slope Indicator (VGSI) and Obstacle Protection. Operators should discuss the need to comply with the VGSI, if available, and discussion of the obstacle protection the VGSI provides in the visual segment. ### Page 22 Advisory Circular Feedback Form If you find an error in this AC, have recommendations for improving it, or have suggestions for new items/subjects to be added, you may let us know by contacting the Flight Technologies and Procedures Division at 9-AWA-AFS400-Coord@faa.gov or the Flight Standards Directives Management Officer at 9-AWA-AFB-120-Directives@faa.gov. Subject: AC 120-108A, Continuous Descent Final Approach Date: _____________________ Please check all appropriate line items: An e rro r (pro cedural or typographical) has been noted in paragraph ____________ on page _______. Recommend paragraph _____________ on page __________ be changed as follows: ______________________________________________________________________ ______________________________________________________________________ In a future change to this AC, please cover the following subject: (Briefly describe what you want added.) ______________________________________________________________________ ______________________________________________________________________ Other comments: ______________________________________________________________________ ______________________________________________________________________ I would like to discuss the above. Please contact me. 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