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:
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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
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.
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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.
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.
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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.
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.
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