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.
3-2 Figure 3-1. Instrument Approach Procedures 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.
3-5 Figure 3-2. Climb/Descent Table (Not for Navigation)