FLIGHT OPERATIONS PANEL

International Civil Aviation Organization 24/04/2015 WORKING PAPER FLIGHT OPERATIONS PANEL WORKING GROUP SECOND MEETING (FLTOPSP/WG/2) Rome, Italy, 4 to 8 May 2015 Agenda Item 4 : Active work programme items 4.1: PBN Operational Implementation Issues Next Steps for Continuous Descent Final Approach Operations (CDFA) (Presented by Mr. Chris Hope) SUMMARY This paper describes the additional guidance material that is necessary to better explain better the use of aircraft vertical navigation systems and addresses using a Minimum Descent Altitude (MDA) as a Decision Altitude (DA) without an altitude additive during Continuous Descent Final Approach (CDFA) operations. This paper is submitted as tasked by the All Weather Operations Harmonization Aviation Rule Making Committee (AWOH ARC). 1. INTRODUCTION 1.1 There is insufficient guidance material available to explain the use of aircraft vertical navigation systems in ICAO documentation. Additionally, States allow Minimum Descent Altitude (MDA) as a Decision Altitude (DA) operation during CDFA in ways that differ. Again, the current guidance material is insufficient on this topic. Also be aware that the situation is different in states that apply state minima and those that don t. 2. BACKGROUND/DISCUSSION 2.1 For many years there were two types of instrument approach procedures, precision and non-precision. States developed their operational procedures for flying precision and nonprecision approaches consistent with the way the approach was designed. The average pilot is 1

probably not an expert in procedure design criteria, however he or she knows a few absolute truths and knows not to ever violate them or obstacle protection may not be guaranteed. For example, pilots are taught that they cannot go lower than the MDA on a non-precision instrument approach procedure unless they have the proper visual references and the aircraft is continuously in a position from which a descent to landing on the intended runway can be made at a normal rate of descent using normal manoeuvres. The operational procedure of stepping down at each published altitude constraint, dive and drive, on non-precision approach procedures comes from this understanding of the procedure design. The pilot knows he or she will not hit any obstacles as long as he or she does not go below MDA until the runway is in sight and the aircraft is in a safe position to land. If the pilot does not see the runway or is not in a safe position to land, the pilot will initiate the missed approach procedure at the missed approach point. On precision instrument approach procedures, pilots are taught that they cannot continue below to the Decision Altitude/Height (DA/H) unless they have acquired the visual references and the aircraft is a safe position to land. The vertical operational procedure of dive and drive is not applicable to a precision approach, since the pilot is taught to follow the continuous descent guidance provided by the glide path. If pilots elect to execute a missed approach at DA, they know that they will go below the DA slightly as the missed approach initiation arrests the descent rate and initiates a climb. The pilot may not know the obstacle protection surfaces but knows it is okay to go lower than the DA during the missed approach. Again, the operational procedure matches the procedure design. 2.2 A leading cause of worldwide commercial aviation fatal accidents throughout the years has been controlled flight into terrain or CFIT. A key contributor to CFIT is unstabilized approaches. A stabilized approach can be characterized by maintaining a stable approach speed, descent rate, vertical flight path, and configuration to the landing touchdown point, usually from 1,000 feet above the airport elevation. With this definition, the dive and drive technique for a nonprecision instrument approach procedure is an unstabilized approach and is implied to be less safe. ICAO has recommended CDFA technique where possible to reduce the risk of CFT because CDFA utilizes the stable approach criteria. Another way of saying this is that ICAO has recommended the pilot use adjusted operational procedures for the precision instrument approach to fly non-precision instrument approach procedures. 2.3 The benefits of CDFA are well-known, but states need to ensure their operators do not do something during CDFA that could cause an unsafe situation. The best way to do this is to ensure nothing in the operational guidelines invalidates and possibly compromises the provided obstacle clearance in the procedure design. One of the primary tasks on the job card is to look at DA in lieu of MDA operations during CDFA. For the purpose of this paper, DA in lieu of MDA will be defined as using a MDA as a DA without an altitude additive. The design of the non-precision instrument approach procedure should be evaluated before considering MDA as a DA operation. The question must be asked and answered if it is safe to go below the MDA on a non-precision instrument approach procedure during the initiation of the missed approach procedure. It cannot be assumed that the required obstacle clearance based on level flight at the MDA will be adequate if the aircraft dips below the MDA using the CDFA technique during the missed approach manoeuvre. The rest of the missed approach path should be evaluated when the non-precision approach procedure is considered for CDFA operations. The missed approach point for some non-precision procedures is very close to the runway end. This is one of the most compelling reasons for using CDFA because it can prevent the late, steep descent from MDA to try to save an approach. However, the area evaluated for missed approach is different for precision and non-precision approaches as well as the energy state of the aircraft. It is assumed the aircraft will be in level flight for a non-precision instrument approach when the pilot initiates the missed approach. This will not be the case if the pilot is flying CDFA and 2

initiates a missed approach at MDA. This CDFA missed approach profile should be evaluated to ensure all potential obstacles are accounted for in the missed approach. Lastly, the visibility actually needed to see the required visual references will be different for CDFA compared the step down or dive and drive technique. With the application of the CDFA technique, the point where the pilot has to make the decision to continue the approach or go-around could be significantly farther away from the runway end than the charted missed approach point. If the visibility required for the approach is based upon a missed approach point at the runway threshold, it likely will not be sufficient to see the required visual references at the CDFA DA. In summary, CDFA has been demonstrated to be a safe and preferable technique to fly non-precision instrument approach procedure, but the operator must consider and evaluate the actual charted procedure with the CDFA operation to ensure it is safe to use MDA as a DA. 2.4 Additionally, the method of the vertical path guidance should be considered when conducting CDFA operations. There are several techniques for glidepath control when conducting CDFA. EASA AMC1 CAT.OP.MPA 115 describes three choices to control the descent path on CDFA: a recommended descent rate, based on estimated ground speed; a descent path depicted on the approach chart; or a descent path coded in the flight management system in accordance with the approach chart descent path. EASA guidance states that all three techniques control the path to the DA/DH. Some other states guidance material defines the two terms, advisory vertical guidance and approved vertical guidance. Advisory vertical guidance is typically an optional capability implemented at the manufacturer s discretion that can aid the pilot in flying CDFA but is not certified to use to APV or SBAS CAT I minimums on an instrument approach procedure. For RNAV procedures, approved vertical guidance provides vertical deviation guidance indications generated by certified means and is approved for APV or SBAS CAT I lines of minima. Both can be used on nonprecision approach procedures for CDFA but should both be used for MDA as DA operations? Annex 6 and PANS-OPS consider CDFA operations with advisory and approved vertical guidance to be 3D instrument approach operations but is silent if they can be flown to a MDA as a DA without some kind of additive. A recommended descent rate, based on ground speed is a manual calculation; Annex 6 considers that a 2D instrument approach operation and it should not be flown to a MDA as a DA unless an additive is applied. 2.5 Charting of CDFA has caused some confusion among operators. Most of this confusion comes from the charting of DA minimums on non-precision instrument approach procedures. It is important to note that CDFA is a technique to fly a non-precision instrument approach procedure. There are no CDFA criteria in PANS-OPS or United States Standard for Terminal Procedures (TERPS). Since there is no standard, there are significant inconsistencies on the charting of the application of the CDFA technique to non-precision approaches. Some States or route manual producers publish a separate DA for CDFA on the chart as well as a MDA for an operator who chooses not to use CDFA. Some States or route manual producers will only publish a DA for all non-precision instrument approaches, assuming the operator is using CDFA. However, there is no annotation on the chart identifying if there has been any obstacle clearance evaluation below the MDA of the procedure to ensure compatibility with the use of a MDA as a DA. It is still the responsibility of the State of the operator to approve the method that the operators use to determine the minimums, but that is complicated if the aerodrome operating minima is confusing and not in accordance with ICAO standards. 2.6 In summary, the AWOHARC has three broad recommendations for the use of MDA as a DA during CDFA operations. First, coordinate with the IFPP to determine if it is necessary to develop criteria in PANS-OPS, Vol. II to evaluate the non-precision instrument approach procedure 3

for capability and safety to use MDA as a DA. Attached to this paper is an example of the procedure review that the FAA uses for MDA as a DA. Second, develop definitions of approved vertical guidance and advisory guidance and determine the types of vertical guidance that are acceptable to use in MDA as DA operations. Finally, work with the IFPP to develop criteria for charting CDFA operations that will eliminate the confusion and doubt about what can be safely flown on the procedure design. 3. ACTION BY THE MEETING 3.1 The FLTOPSP/WG/2 is invited to: a) Note contents of this working paper b) Agree, as may be amended, with the action items contained in paragraph 2.5 Attachments Sample Operations Specification for MDA as a DA 4

Attachment 1 Sample Operations Specification Vertical Navigation (VNAV) Instrument Approach Procedures (IAP) Using Minimum Descent Altitude (MDA) as a Decision Altitude (DA)/Decision Height (DH) a. The certificate holder is authorized to use minimum descent altitude (MDA) as a decision altitude (DA)/decision height (DH) with vertical navigation (VNAV) on a nonprecision approach (NPA). The certificate holder will use operations specification C073 in conjunction with operations specification C052, Straight-In Non-Precision, APV, and Category I Precision Approach and Landing Minima All Airports. The certificate holder is authorized to conduct instrument approach operations using the following aircraft and area navigation (RNAV) systems certified for these VNAV operations as listed in Table 1 below. Airplane Type (M/M/S) Table 1 - Authorized Aircraft and Equipment Area Navigation System (Model/Version) Remarks b. Public Vertically Guided Instrument Approach Procedure (IAP) Assessment. Obstacle clearance surface (OCS) assessments protect the instrument procedure, including the missed approach. Glidepath qualification surface (GQS) assessments protect the landing area and are accomplished on 14 CFR Part 97 IAPs with a published DA/DH. These approaches conform to the U.S. standard for Terminal Instrument Procedures (TERPS) and include instrument landing system (ILS), Ground Based Augmentation System (GBAS) Landing System (GLS), RNAV Required Navigation Performance (RNP) and RNAV Global Positioning System (GPS) IAPs with a localizer performance with vertical guidance (LPV) DA and/or lateral navigation (LNAV)/VNAV DA. NOTE : The use of MDA as a DA/DH does not ensure obstacle clearance from the MDA to the landing runway. The certificate holder must see and avoid obstacles between the MDA and the runway when 14 CFR part 91, 91.175 requirements are met and the approach is continued below the MDA for landing. c. Authorized Approaches. The certificate holder may fly all Part 97 nonprecision straight-in IAPs listed as authorized in their C052, Table 1, columns 1 and 2 using an MDA as a DA/DH if the approach meets one of the following requirements and its subcomponents: (1) Serves a runway that has a published RNAV IAP R( NAV (GPS), "RNAV (RNP)" or Att 1-1

"GPS" in the title) with a published LNAV/VNAV or RNP DA and: (a) Has the exact published final approach course as the RNAV IAP. (b) Has a published vertical descent angle (VDA) coincident with or higher than the barometric vertical guidance (glide slope(gs)) on the published RNAV IAP. (i) A published VDA is not required when using the LNAV minima line on an RNAV approach that has a published LPV and/or LNAV/VNAV DA. Use the published GS. The VNAV path must be at or above all stepdown fixes. (c) Is selected from an approved and current database and the flight management system (FMS) displays a final approach Flight Path Angle (FPA) in tenths or hundredths. The displayed FPA may have a maximum difference of minus.04 degrees from the IAP VDA or GS. The displayed FPA may always be rounded up to the next tenth. The range for a given FPA will be 2.9 to 3.0, 3.1 to 3.2, 3.2 to 3.3, 4.0 to 4.1, etc. This applies to systems that display the FPA in tenths or hundredths. NOTE : Aircraft without an FMS FPA display meeting previous AC 20-129 criteria may have been approved for LNA/VNAV approaches using barometric vertical navigation (baro-vnav). The certificate holder currently approved C073, using AC 2-0129 criteria, may continue C073 operations. (2) Serves a runway that has a published ILS, GLS, or RNP IAP with LPV minima and: (a) Has the exact published final approach course as the ILS, GLS, or RNP IAP. (b) Has a published VDA coincident with or higher than the electronic GS on the published ILS, GLS, or RNP IAP. (i) A published VDA is not required on a LOC-only approach when the ILS GS is out of service. Use the published GS. The VNAV path must be at or above all stepdown fixes. (ii) A published VDA is not required when using LNAV minima on an RNAV approach that has a published LPV or LNAV/VNAV DA. Use the published GS. The VNAV path must be at or above all stepdown fixes. (c) Is selected from an approved and current database and the FMS displays a final approach FPA in tenths or hundredths. The displayed FPA may have a maximum difference of minus.04 degrees from the IAP VDA or GS. The displayed FPA may always be rounded up to the next tenth. The range for a given FPA will be 2.9 to 3.0, 3.1 to 3.2, 3.2 to 3.3, 4.0 to 4.1, etc. This applies to systems that display the FPA in tenths or hundredths. NOTE : Aircraft without an FMS FPA display meeting previous AC 20-129 criteria may have been approved for LNA/VNAV approaches using baro-vnav. The certificate holder currently approved C073, using AC 20-129 criteria, may continue C073 operations. (3) Serves a runway to an airport operating under 14 CFR Part 139 with a Visual Glide Slope Indicator (VGSI). (a) The VDA or GS on the published final approach course must be coincident with or higher than the published VGSI descent angle. (b) The published final approach course is within plus or minus 4 degrees of the runway centerline (RCL) course. Att 1-2

3 d. VNAV Path Angle. The VNAV path angle must be greater than 2.75 and less than 3.77 degrees for Category A, B, and C aircraft, and greater than 2.75 and less than 3.50 degrees for Category D/E aircraft. e. Operational Restriction. The certificate holder will not use an MDA as a DA/DH if the requirements specified in this operations specification are not met. The certificate holder may use a continuous descent final approach (CDFA), but will begin the missed approach at an altitude above the MDA that will not allow the aircraft to descend below the MDA. f. Required Training. Flightcrews must be trained in accordance with the certificate holder s approved training program for the navigation system and instrument procedure being used before conducting any operations authorized by this operations specification. END Att 1-3