Vertical Path Control on Non-Precision Approaches
|Issuing Office:||Standards||Document No.:||AC 700-028|
|File Classification No.:||Z 5000-34||Issue No.:||01|
|RDIMS No.:||8193925-V13||Effective Date:||2013-04-22|
Table of Contents
- 1.0 INTRODUCTION
- 2.0 REFERENCES AND REQUIREMENTS
- 3.0 BACKGROUND
- 4.0 AIRCRAFT ELIGIBILITY REQUIREMENTS
- 5.0 FLIGHT CREW MEMBER DETERMINATION OF THE ANGULAR VERTICAL PROFILE
- 6.0 INFORMATION MANAGEMENT
- 7.0 DOCUMENT HISTORY
- 8.0 CONTACT OFFICE
- APPENDIX 1 – VERTICAL PROFILE TABLES
- APPENDIX 2 – APPROACH CHART EXAMPLES
- This Advisory Circular (AC) is provided for information and guidance purposes. It describes an example of an acceptable means, but not the only means, of demonstrating compliance with regulations and standards. This AC on its own does not change, create, amend or permit deviations from regulatory requirements, nor does it establish minimum standards.
The purpose of this AC is to promote the use of stabilized techniques during non-precision approach (NPA) procedures where such a technique would enhance the safety of the flight. It is intended that the updated language of this AC will make it clear that the stabilized techniques described herein are available to the entire Canadian civil aviation community. It is hoped that a greater number of flights will adopt the stabilized criteria inherent to these types of techniques, and that the level of safety will increase as a consequence.
The purpose of this AC is to announce the related NPA chart depiction changes which will be introduced by NAV CANADA. NAV CANADA will include the publication of a constant descent angle on NPA charts in a joint effort to promote the use of a stabilized approach technique during the conduct of non-precision approaches.
This AC applies to all Canadian flight crew members (including general aviation), air operators holding an Air Operator Certificate issued under Part VII of the Canadian Aviation Regulations (CARs) and private operators holding a Private Operator Certificate issued under Subpart 604 of the CARs.
This document is also applicable to all Transport Canada Civil Aviation (TCCA) employees, and to individuals and organizations when they are exercising privileges granted to them under an External Ministerial Delegation of Authority. The content of this document is also available to the aviation industry at large for information purposes.
The guidance contained in this AC is specific to non-precision approaches. The vertical path control and guidance available during an approach with vertical guidance (APV) or precision approach does not fall within the scope of this AC.
1.3 Description of Changes
- Not applicable.
2.0 REFERENCES AND REQUIREMENTS
2.1 Reference Documents
The following reference material may be consulted for information purposes:
Part V of the Canadian Aviation Regulations (CARs)—Airworthiness;
Part VI, subpart II of the CARs—Operating and Flight Rules;
Part VI, subpart IV of the CARs—Private Operator Passenger Transportation;
Part VII, subpart II of the CARs—Aerial Work;
Part VII, subpart III of the CARs—Air Taxi Operations;
Part VII, subpart IV of the CARs—Commuter Operations;
Part VII, subpart V of the CARs—Airline Operations;
Standard 722 of the Commercial Air Services Standards (CASS)—Aerial Work;
Standard 723 of the CASS—Air Taxi;
Standard 724 of the CASS—Commuter Operations;
Standard 725 of the CASS—Airline Operations;
Transport Canada Publication (TP) 308 —Criteria for the Development of Instrument Procedures;
Flight Safety Foundation Approach and Landing Accident Reduction (ALAR) Toolkit;
Federal Aviation Administration Advisory Circular 120-108—Continuous Descent Final Approach; and
International Civil Aviation Organization (ICAO) Doc 8168, Procedures for Air Navigation Services/Aircraft Operations (PANS/OPS), Vol. I—Flight Procedures.
2.2 Cancelled Documents
As of the effective date of this document, the following document is cancelled:
- Commercial and Business Aviation Advisory Circular (CBAAC) No. 0238, 2006-09-08—Stabilized Constant Descent Angle Non-Precision Approach.
- By default, it is understood that the publication of a new issue of a document automatically renders any earlier issues of the same document null and void.
2.3 Definitions and Abbreviations
- The following definitions are used in this document:
Barometric Vertical Navigation (baro-VNAV): A function of certain area navigation (RNAV) systems which presents computed vertical guidance to the flight crew member, referenced to a specified vertical path. The computed vertical guidance is based on barometric altitude information and is typically computed as a geometric path between two waypoints or an angle based on a single waypoint.
Constant Descent Final Approach (CDFA): A technique, consistent with stabilized approach procedures, for flying the final approach segment of a non-precision instrument approach procedure as a continuous descent, without level-off, from an altitude/height at or above the final approach fix altitude/height to a point approximately 50 feet (ft.) above the landing runway threshold or the point where the flare manoeuvre should begin for the type of aircraft flown (ICAO).
Controlled Flight Into Terrain (CFIT): An occurrence in which an aircraft, under the control of the crew, is flown into terrain, water or an obstacle with no prior awareness on the part of the crew of the impending disaster.
- The following abbreviations are used in this document:
- AC: Advisory Circular;
- ALAR: Approach and Landing Accident Reduction;
- APV: Approach With Vertical Guidance;
- CDFA: Constant Descent Final Approach;
- CFIT: Controlled Flight Into Terrain;
- FAF: Final Approach Fix;
- FPM: Feet Per Minute;
- MAP: Missed Approach Point;
- MDA: Minimum Descent Altitude;
- NPA: Non-Precision Approach;
- SCDA: Stabilized Constant Descent Angle;
- WAAS: Wide Area Augmentation System.
- The material described in this Advisory Circular (AC) is based on the Flight Safety Foundation Approach and Landing Accident Reduction (ALAR) Toolkit and International Civil Aviation Organization (ICAO) Standards and Recommended Practises.
- Controlled Flight Into Terrain (CFIT) continues to be major threat to the safety of the civil aviation industry in Canada. The need for a stabilized final approach during non-precision approaches (NPAs) has been recognized by the ICAO CFIT Task Force as an aid to prevent CFIT accidents. The step-down technique presumed by the NPA procedure design may have been appropriate to early piston transport aircraft, but larger jet transport aircraft are less suited for this type of profile.
- In using the step-down technique, the aircraft flies a series of vertical descents during the final approach segment as it descends and levels off at the minimum Instrument Flight Rules (IFR) altitudes published for the approach. The descents and levels-off result in significant changes in power settings and pitch attitudes, and in some aircraft may prevent the landing configuration from being established until landing is assured. Using the step-down technique, the aircraft may be flown at the minimum altitudes, and consequently exposed to reduced obstacle separation, for extended periods of time. A premature descent or a missed level-off exposes the aircraft to a CFIT accident potential.
- Many air operators require their crews to use a stabilized approach technique which is entirely different from that envisaged in the original NPA procedure design. A stabilized approach is calculated to achieve a constant rate of descent at an approximate 3° flight path angle; with stable airspeed, power setting, and attitude; and with the aircraft configured for landing. The safety benefits derived from a stabilized final approach have been recognized by many organizations including ICAO, the Federal Aviation Administration, and Transport Canada Civil Aviation (TCCA). Those air operators not already doing so are encouraged to incorporate stabilized approach criteria into their Standard Operating Procedures (SOPs) and training syllabi.
3.1 Stabilized Approach
- An approach is considered stabilized when it satisfies the associated conditions, typically defined by an air operator in their Company Operations Manual (COM) or SOPs, as they may possibly relate to:
- range of speeds specific to the aircraft type;
- power setting(s) specific to the aircraft type;
- range of attitudes specific to the aircraft type;
- configuration(s) specific to the aircraft type;
- crossing altitude deviation tolerances;
- sink rate; and
- completion of checklists and flight crew briefings.
- Stabilized approach criteria should be defined for all approaches and may include:
- that flights shall be stabilized by no lower than 1,000 feet (ft.) above the threshold when in instrument meteorological conditions (IMC);
- that all flights shall be stabilized by no lower than 500 ft. above the threshold;
- that the flight remain stabilized until landing
- that if an approach is not stabilized in accordance with these requirements, or has become destabilized afterwards, a go-around is required.
4.0 VERTICAL PATH CONTROL TECHNIQUES
There are typically three vertical path control techniques available for an NPA:
- Constant Descent Angle; or
- Stabilized Constant Descent Angle (SCDA).
Note. Constant Descent Angle is equivalent to ICAO’s Constant Angle Descent, and SCDA is considered a form of ICAO’s Constant Descent Final Approach (CDFA). In the interest of respecting terminology already in use in the Canadian civil aviation industry, and standardization with NAV CANADA charting, the above terminology has been adopted.
- While the NPA procedures themselves are not inherently unsafe, the use of the step-down descent technique to conduct an NPA is prone to error, and is therefore discouraged where other methods are available. In using the step-down technique during the final approach segment, the flight crew member flies an unstable vertical profile; descending and levelling off at the minimum altitudes published for the approach and then, if the required visual references have been acquired, descending from Minimum Descent Altitude (MDA) to a landing.
- The risks associated with conducting an NPA can be mitigated by using an angular vertical profile instead of the step-down technique described above. The use of an angular vertical profile increases the likelihood of the approach being conducted in a stabilized manner.
- When conducting an NPA using an angular vertical profile, the vertical path may be intercepted prior to the Final Approach Fix (FAF) at a higher altitude.
- The angle to be used for an angular vertical path is ideally obtained from the approach chart. If the approach chart does not contain a published constant descent angle, the angle may be calculated using a method approved as part of an air operator’s SOPs, or by means of tables as those found in Appendix 1 of this AC. Flight crew members must be aware of the risks associated with manually calculating the descent angle as a calculation error could lead to the use of the wrong descent angle. It is strongly recommended that flight crew members become comfortable and proficient with the manual calculation of the descent angle before doing so under high workload conditions.
- Regardless of the type of vertical path control technique that is used on an NPA, the lateral “turning” portion of the missed approach shall not be executed prior to the Missed Approach Point (MAP). However, the climb portion of a missed approach procedure may be commenced from any point along the final approach.
- Except in the case of an air operator conducting operations in accordance with an exemption to Paragraph 602.128(2)(b) of the Canadian Aviation Regulations (CARs), a flight crew member may not descend below the MDA if the visual references required to land have not been acquired. In order to respect this requirement, an additive to the MDA may be required to ensure the aircraft does not descend below MDA during the transition from a descent to the climb required by a missed approach procedure.
- Commencing in 2013, NAV CANADA will begin the publication of approach charts which include constant descent angle information in a tabular form and in the profile view. The inclusion of this information is intended to facilitate the use of the stabilized approach techniques described in this AC. Refer to Appendix 2 of the AC for examples.
- Regardless of the vertical path control technique used on an NPA, a temperature correction must be applied to all minimum altitudes during cold weather operations.
- To facilitate the stabilized descent, some avionics such as Barometric Vertical Navigation (baro-VNAV) and Wide Area Augmentation System (WAAS) capable systems generate a calculated vertical profile and the guidance to follow this profile. When conducting an NPA, the vertical guidance generated by the navigation system is advisory only. Flight crew members must use the barometric altimeter as the primary altitude reference to ensure compliance with any and all altitude restrictions. WAAS capable equipment requires special consideration when using advisory vertical guidance and flight crew members should refer to the manufacturer’s operating guides or limitations.
- Example: The following approach conditions will be used to demonstrate the techniques.
Figure 1 - Sample approach conditions
4.2 Step Down Technique
- Inherently unstable;
- Higher workload during the approach;
- Multiple possible level flight segments;
- The rate-of-descent (descent angle) is inconsistent throughout the approach;
- Higher fuel consumption.
- Descent Profile – Step-Down Technique.
Figure 2 – Illustration of Step-Down Technique
- Using the step-down technique, the aircraft is flown level at minimum altitudes for extended periods of time. Once inbound to the FAF on the intermediate segment, the aircraft is descended to and levelled at the minimum FAF crossing altitude. After crossing the FAF and on the final approach segment, the aircraft is descended to and levelled at the MDA, as well as any intermediate step-down altitudes between the FAF and the MAP. The aircraft is flown level at the MDA until encountering visual conditions sufficient to continue the approach to land, or it reaches the MAP where a missed approach is commenced. In order to improve the likelihood of completing a normal descent and landing after reaching the MDA in minimum weather conditions, the aircraft should be level at the MDA at a distance equal to or greater than the published visibility minima prior to the MAP.
- Careful attention to altitude control is required with this technique since it involves high rates of descent and a greater amount of time at an altitude which provides only the minimum separation from obstacles.
4.3 Constant Descent Angle
- Inherently stable until MDA level-off;
- Lighter workload during the approach than the step-down technique;
- One possible level flight segment;
- Better fuel efficiency.
- Descent Profile – Constant Descent Angle
Figure 3 – Illustration of Constant Descent Angle
- The descent shall be flown to pass at or above the minimum altitude at any step-down fix. This technique involves achieving a constant angular descent profile from the FAF, or optimum point on procedures without a FAF, to a reference datum above the runway threshold (typically 50 ft.). When the aircraft approaches the MDA, a decision shall be made, dependent on visual conditions, to either continue on the constant descent angle to the runway without any intermediate level-off; or:
- level off at or above the MDA; and
- continue inbound until:
- encountering visual conditions sufficient to continue the approach to land; or
- reaching the published MAP and commencing a missed approach procedure.
4.4 Stabilized Constant Descent Angle
- Inherently stable;
- Lighter workload during the approach;
- No level flight segment. The descent continues to a landing or to the climb portion of a missed approach;
- Better fuel efficiency.
- Descent Profile – Stabilized Constant Descent Angle (SCDA)
Figure 4 – Illustration of Stabilized Constant Descent Angle
- The SCDA technique simplifies the final segment of the NPA by incorporating techniques similar to those used when flying a precision approach procedure or an approach procedure with vertical guidance. This technique improves flight crew member situational awareness and is entirely consistent with the “stabilized approach” criteria.
- An operations specification (Ops Spec) is not required to use the SCDA technique. However, private operators and air operators should address SCDA in their training programs and COMs in order to ensure the technique is applied uniformly within their operation.
- The descent shall be flown to pass at or above the minimum altitude at any step-down fix. The rate of descent is selected and adjusted to achieve a continuous descent to a point approximately 50 ft. above the landing runway threshold or the point where the flare manoeuvre should begin for the type of aircraft flown. This technique requires a continuous descent, without levels-off, to be flown based on the descent angle obtained from the approach chart or the descent angle determined by the flight crew member.
- When the aircraft approaches the MDA, a decision shall be made, dependent on visual conditions, to either continue on the constant angle to the runway or commence the vertical (climbing) portion of the missed approach. At no time is the aircraft flown in level flight at or near the MDA.
- The use of the SCDA technique may be required as a condition to Ops Specs 019, 303 and 503 Approach Ban Operations, which authorize the use of lower approach ban minima than those found in Section 700.10 of the CARs. When using the SCDA technique in an activity permitted by these Ops Specs, additional regulatory requirements as found in Sections 703.41, 704.37 and 705.48 of the CARs must be met.
5.0 FLIGHT CREW MEMBER DETERMINATION OF THE ANGULAR VERTICAL PROFILE
This section describes how a flight crew member may determine the descent gradient, descent angle or descent rate from the tables found in Appendix 1 of this AC, when an approach chart does not contain a constant descent angle.
Interpolation and extrapolation are permitted in the use of these tables.
Note. Whenever possible, the required descent angle should be obtained from the approach chart. The calculation, or determination from a table, of the constant descent angle or descent gradient should only be done in flight by flight crew members who are comfortable and proficient with the process.
5.1 Determination of constant descent angle or gradient from the tables
Determine the altitude difference between the FAF crossing altitude and the step down fix altitude (Example: 1500 ft. – 1200 ft. = 300ft). If there is no step down fix between the FAF and the runway, determine the altitude difference between the FAF crossing altitude and the runway elevation.
Determine the distance between the FAF and the step-down fix (Example: 2 Nautical Mile(s) (NM)). If there is no step-down fix between the FAF and the runway, determine the distance between the FAF and the runway threshold.
On Table 1 for the constant descent angle or Table 2 for the descent gradient, locate where the column related to the above-described distance intersects the row related to the above-described altitude.
5.2 Determination of descent rate from the tables
- Determine the required constant descent angle from the approach chart. If the approach chart does not contain a published constant descent angle, determine the required constant descent angle or descent gradient using the procedure described above.
- Locate on Table 3 where the row related to the above-described constant descent angle or descent gradient intersects the column related to the aircraft ground speed during the approach.
5.3 Calculation of descent gradient and rate
- Determine the altitude difference between the FAF crossing altitude and the step down fix altitude (Example: 1500 ft. – 1200 ft. = 300 ft.). If there is no step down fix between the FAF and the runway, determine the altitude difference between the FAF crossing altitude and the runway elevation.
- Determine the distance between the FAF and the step-down fix (Example: 2 NM). If there is no step-down fix between the FAF and the runway, determine the distance between the FAF and the runway.
- To determine the descent gradient, divide the altitude difference by the distance to be flown (Example: 300 ft. ÷ 2NM = 150 ft./NM).
- If calculation of the descent rate is desired, multiply the descent gradient by the ground speed in NM/minute.
- Example 1: 120 Knot ground speed equates to 2 NM/minute. 150ft/NM x 2 NM/minute = 300 Feet per Minute (FPM) required descent rate.
- Example 2: 180 Knot groundspeed equates to 3 NM/minute. 150’/NM x 3 NM/minute = 450 FPM required descent rate.
5.4 Effect of Temperature on the Vertical Profile
Note. The following does not apply to aircraft which use WAAS or compensated baro-VNAV as the basis for vertical navigation.
- The tables and calculations described above rely on a barometric change to measure the vertical component of the descent profile. This barometric change will not be consistent as the ambient temperature varies from the International Standard Atmosphere (ISA). If the ambient temperature is colder, the air will be denser which will result in the target barometric change occurring in a smaller actual altitude change. The result will be a shallower than targeted profile. For example, a nominal 3° glide path may be closer to 2.5° at very low temperatures. The opposite occurs when the ambient temperature is higher than ISA.
Table 1 - Effect of temperature on descent angle (sea level) Deviations from Target 3° Descent Angle
True Descent Angle
6.0 KNOWLEDGE AND TRAINING REQUIREMENTS
- Not applicable.
7.0 DOCUMENT HISTORY
8.0 CONTACT OFFICE
For more information, please contact the:
Chief, Commercial Flight Standards - AARTF
Suggestions for amendment to this document are invited, and should be submitted via:
Original signed by Aaron McCrorie on April 19, 2013
Transport Canada documents or intranet pages mentioned in this document are available upon request through the Contact Office.
APPENDIX 1 – VERTICAL PROFILE TABLES
|DESCET ANGLE TABLE (°)|
|DESCENT GRADIENT TABLE (ft/NM)|
|Altitude (ft)||Distance (NM)|
|DESCENT RATE TABLE|
APPENDIX 2 – APPROACH CHART EXAMPLES