U.S. Department

of Transportation

Federal Aviation

Administration

Advisory

Circular

Subject: Airworthiness Approval of Enhanced 

Vision System, Synthetic Vision System, 

Combined Vision System, and Enhanced 

Flight Vision System Equipment

Date:

Initiated by: AIR-130

AC No: 20-167A 

Foreword

This advisory circular (AC) provides guidance for gaining airworthiness approval for 

enhanced and synthetic vision systems in aircraft. Specifically, it provides one 

acceptable means for complying with Title 14 of the Code of Federal Regulations (14 

CFR) part 23, 25, 27, or 29 airworthiness regulations when installing a synthetic vision 

system (SVS), enhanced vision system (EVS), combined vision system (CVS), or 

enhanced flight vision system (EFVS) in an airplane or rotorcraft. 

David W. Hempe

Manager, Aircraft Engineering Division
MM/DD/YYYY AC 20-167A

ii

Table of Contents

Paragraph Page

Chapter 1. Introduction .............................................................................................................. 1

1-1. Purpose............................................................................................................................ 1

1-2. AC Audience................................................................................................................... 1

1-3. Applicability ................................................................................................................... 1

1-4. How to Use This Document............................................................................................ 1

1-5. Cancellation .................................................................................................................... 2

Chapter 2. Vision Systems Overview ......................................................................................... 3

2-1. Enhanced Vision Systems............................................................................................... 3

2-2. Synthetic Vision Systems ............................................................................................... 4

2-3. Combined Vision Systems.............................................................................................. 7

2-4. Enhanced Flight Vision Systems.................................................................................... 7

Chapter 3. Airworthiness Package Contents........................................................................... 11

3-1. Airworthiness Package.................................................................................................. 11

3-2. Intended Function. ........................................................................................................ 11

Chapter 4 System Criteria ......................................................................................................... 13

4-1. EVS or SVS (or CVS when EVS and SVS combined) – General................................ 13

4-2. EVS Specific Criteria.................................................................................................... 16

4-3. SVS Specific Criteria.................................................................................................... 17

4-4. CVS Specific Criteria. .................................................................................................. 21

4-5. EFVS – General and Specific Criteria........................................................................... 21

Chapter 5. Systems Installation Considerations..................................................................... 31

5-1. EVS/SVS/CVS Installations Considerations................................................................ 31

5-2. EFVS Installation Considerations................................................................................. 33

5-3. HIRF Considerations for All Installations (EVS, SVS, CVS, and EFVS). .................. 37

Chapter 6. Performance Evaluation ........................................................................................ 38

6-1. EVS/SVS/EFVS Performance Demonstration ............................................................. 38

6-2. Performance Demonstration of EFVS II....................................................................... 39

6-3. Environmental Qualification......................................................................................... 40

Appendix 1. FAA EFVS 14 CFR Compliance (Partial List).............................................. A1-1

1-1. Airworthiness Standards. .......................................................................................... A1-1

1-2. EFVS Compliance. ................................................................................................... A1-1
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Appendix 2. EFVS I and EFVS II Systems Safety Guidance ............................................ A2-1

2-1. General...................................................................................................................... A2-1

2-2. Required Level of Safety. ......................................................................................... A2-1

2-3. Demonstration........................................................................................................... A2-2

2-4. State Data.................................................................................................................. A2-2

Appendix 3. EFVS I and II Safety Standards..................................................................... A3-1

3-1. Safety factors for EFVS described in this AC .......................................................... A3-1

3-3. Demonstration........................................................................................................... A3-2

Appendix 4. Sample EFVS I Flight Test Considerations................................................... A4-1

4-1. General Flight Test Considerations. ......................................................................... A4-1

4-2. Minimum Flight Test Conditions Observed. ............................................................ A4-1

4-3. Test Points................................................................................................................. A4-2

4-4. Evaluation During Taxi............................................................................................. A4-2

4-6. Climb and Descent and Lateral Modes Evaluation................................................... A4-3

4-7. Instrument Approaches. ............................................................................................ A4-3

4-8. Flare Landing and Go Around .................................................................................. A4-3

4-9. Copilot Monitor ........................................................................................................ A4-3

4-10. Failure Cases............................................................................................................. A4-3

4-11. Ice Protection System Evaluation ............................................................................. A4-4

4-12. Evaluation Matrix. .................................................................................................... A4-4

Appendix 5. Sample Flight Test Considerations for EFVS II ........................................... A5-1

5-1. General Flight Test Considerations. ......................................................................... A5-1

5-2. Minimum Flight Test Conditions Observed. ............................................................ A5-1

5-3. Test Points................................................................................................................. A5-2

5-4. Evaluation During Taxi............................................................................................. A5-3

5-5. Take off Evaluation................................................................................................... A5-3

5-6. Climb and Descent and Lateral Modes Evaluation................................................... A5-4

5-7. Instrument Approaches to the DA(H)....................................................................... A5-4

5-8. Final Approach from the DA/DH, Flare, Landing and Rollout to Safe Taxi Speed. A5-4

5-9. Rejected Landing ...................................................................................................... A5-4

5-10. Pilot Monitoring (PM) Display................................................................................. A5-4

5-11. Failure Cases............................................................................................................. A5-5

5-12. Ice Protection System Evaluation. ............................................................................ A5-5
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5-13. Evaluation Matrix ..................................................................................................... A5-5

Appendix 6. Sample Airplane Flight Manual (AFM) Supplement ................................... A6-1

Appendix 7. Installation of Enhanced Vision System and or/Synthetic Vision System on 

Rotorcraft ................................................................................................................................ A7-1

7-1. General...................................................................................................................... A7-1

7-2. Applicability. ............................................................................................................ A7-1

7-3. Airworthiness Approval............................................................................................ A7-1

7-4. Design Considerations. ............................................................................................. A7-1

Appendix 8. Additional Part 23 Considerations for Enhanced Vision System/or Synthetic 

Vision System for Situation Awareness Only....................................................................... A8-1

8-1. Introduction............................................................................................................... A8-1

8-2. Terrain Alerting. ....................................................................................................... A8-1

8-3. Moving Map Display that Corresponds to and Complements Synthetic Vision PFD 

Display...................................................................................................................... A8-2

8-4. Minimums Audio Callout Capability........................................................................ A8-2

8-5. Digital Evaluation Model (DEM) Resolution........................................................... A8-2

8-6. Aircraft Flight Manual Supplement (AFMS). .......................................................... A8-3

8-7. SVS Unusual Attitude Recovery. ............................................................................. A8-3

8-8. Pilot Evaluation......................................................................................................... A8-3

Appendix 9. Definitions and Acronyms............................................................................... A9-1

9-1. Definitions................................................................................................................. A9-1

9-2. Acronyms.................................................................................................................. A9-5

Appendix 10. Related Publications..................................................................................... A10-1

10-1. Related Publications................................................................................................ A10-1

10-2. How to Get Publications. ........................................................................................ A10-2

List of Figures

Figure Page

Figure 1. Enhanced Vision Diagram.............................................................................................. 3

Figure 2. Synthetic Vision Diagram .............................................................................................. 5

Figure 3. Minimum Detection Range .......................................................................................... 24

Figure 4. Field of View............................................................................................................ A9-3

List of Tables
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Table Page

Table 1. 14 CFR 91.176 EFVS Visibility and Visual Reference Requirements......................... 23

Table 2. System Operating Phases for Considerations................................................................ 32

Table 3. EFVS Acceptable Methods of Compliance ................................................................ A1-1

Table 4. Required Level of Safety, 14 CFR part 25 Aircraft................................................... A2-1

Table 5. Example EFVS/HUD Functional Hazard Assessment, 14 CFR part 25 Aircraft, ILS 

Approaches to 100 ft Height Above Touchdown, RVR 1200 ft............................................... A2-3

Table 6. EFVS I Evaluation Matrix ......................................................................................... A4-4

Table 7. EFVS II Evaluation Matrix........................................................................................ A5-5
MM/DD/YYYY AC 20-167A

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Chapter 1. Introduction

1-1. Purpose

a. In this advisory circular (AC), the Federal Aviation Administration (FAA) 

provides guidance on airworthiness approvals of enhanced vision system (EVS), synthetic vision 

system (SVS), combined vision system (CVS), and enhanced flight vision system (EFVS) 

equipment installation.

b. Existing ACs address flight guidance symbology, head-up displays (HUD) and 

visual display characteristics (for example, AC 25-11A, Electronic Flight Deck Displays, AC 

25.1329-1B, Approval of Flight Guidance Systems and AC 23.1311-1C Installation of Electronic 

Display in Part 23 Airplanes). For a complete listing of related regulations and guidance, refer to 

Appendix 1. This AC complements existing guidance. 

c. This AC is not mandatory and does not constitute a regulation. This AC describes 

an acceptable means, but not the only means, to install and obtain airworthiness approval for

enhanced and synthetic vision technologies. However, if you use the means described in this AC, 

you must follow it in all aspects.

1-2. AC Audience 

This AC is for airplane and rotorcraft manufacturers, modifiers, and type certification engineers 

seeking certification or installation guidance for their visual display system. Sections 23.773, 

25.773 27.773 and 29.773 address vision systems using a transparent display surface located in 

the pilot’s outside view, such as a head-up-display, head-mounted display, or other equivalent 

display. Such “vision systems” include any EVS, EFVS, SVS, or CVS.

1-3. Applicability

a. This AC applies to all applicants for a new type certificate (TC), an amended type 

certificate (ATC), or a supplemental type certificate (STC), to install enhanced and/or synthetic 

vision systems and equipment. The method of compliance described in this AC can be used to 

obtain a TC, STC, or ATC for an airplane or rotorcraft equipped with SVS, EVS, CVS, or EFVS 

equipment. 

b. This AC does not address operational aspects of vision systems or any changes in 

aircraft operational capability that may result from installation of vision systems. Guidance 

material for the operational aspects of EFVS described in this AC can be found in AC 90-106A,

Enhanced Flight Vision Systems. 

1-4. How to Use This Document

a. This AC provides methods, procedures, and practices acceptable to the FAA for 

complying with regulations. EFVS compliance references are listed in Appendix 1.

b. This material does not alter regulatory requirements.
MM/DD/YYYY AC 20-167A

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c. This AC describes system performance.

d. EFVS safety standards and sample flight test considerations for EFVS conducted 

to 100 feet height above runway touchdown zone elevation (EFVS I) and for EFVS operations 

conducted to touchdown and rollout (EFVS II) are in Appendices 3, 4, and 5, respectively.

e. A sample flight manual supplement is outlined in Appendix 6.

f. Appendix 7 addresses specific installation guidance for EVS and/or SVS on 

rotorcraft. Appendix 8 addresses additional part 23 considerations for situation awareness only.

g. Definitions and acronyms are in appendix 9.

h. Certain material within this AC is from RTCA/DO-315A, Minimum Aviation 

System Performance Standards (MASPS) for Enhanced Vision Systems, Synthetic Vision 

systems, Combined Vision Systems, and Enhanced Flight vision Systems. RTCA/DO-315A is 

copyrighted by RTCA, Inc. and used with permission. Purchase information is in Appendix 9.

1-5. Cancellation

AC 20-167, Airworthiness Approval of Enhanced Vision System, Synthetic Vision System, 

Combined Vision System, and Enhanced Flight Vision System Equipment, dated June 22, 2010, 

is canceled.
MM/DD/YYYY AC 20-167A

3

Chapter 2. Vision Systems Overview

2-1. Enhanced Vision Systems

a. An EVS is an electronic means to provide a display of the forward external scene 

topography through the use of imaging sensors, such as forward looking infrared (FLIR), 

millimeter wave (MMW) radiometry, MMW radar, and/or low-light-level image intensifying. 

EVS need not provide the additional flight information/symbology required in 14 CFR 91.176 on 

a HUD or equivalent display. While Enhanced Vision Systems share a similarity with EFVS 

technology, an EVS does not have to be integrated with a flight guidance system. Furthermore, 

while an EVS may provide additional situation awareness without the additional capabilities 

provided by an EFVS, it provides no credit towards operations conducted under 14 CFR 91.176 

(a) and (b). The elements of an installed EVS are listed below, with the EVS diagram shown in 

Figure 1:

1. EVS sensor system.

2. Display processor.

3. EVS display.

4. Pilot controls/interface.

5. Mounting.

V is ib le

E x t e r n a l S cene

Ene r g y

A tm o spher e

S e nsor

S e nsor

Conver s io n

Sensor

S y s te m

D is p la y 

P r o c e s sor

P ilo t 's E y e

Enhanced 

F li g h t V is i o n 

S y s t e m

A ir c r a ft S ta t e

D a ta

H e a d - up D isplay 

P r ocessin g

H e a d - u p

D ispla y

Enhanced 

V i s ion 

S y s te m

EVS D ispla y

P ilo t C ontr o ls

Figure 1. Enhanced Vision Diagram

(Dashed lines and shading represent individual system boundaries for EVS and EFVS)
MM/DD/YYYY AC 20-167A

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Note: While an EFVS contains all the elements of an EVS, for the purposes of this AC 

any discussion of an EVS excludes an EFVS.

b. The categories of current EVS sensors are passive or active sensors.

1. Passive Sensors: Scene contrast detected by passive infrared sensors can 

be much different than that detected by natural pilot vision. On a dark night, thermal differences 

of objects, not detectable by the naked eye, will be easily detected by many imaging infrared 

systems. However, contrasting colors in visual wavelengths distinguished by the naked eye may

not be visible using an imaging infrared system. Sufficient thermal scene contrast allows shapes 

and patterns of certain visual references to be recognized in the infrared image by the pilot. 

However, depending on conditions, they can also appear different to a pilot in the infrared image 

than they would with normal vision.

2. Active Sensors: Scene contrast by active systems depends on several 

parameters such as: whether the transmitter is centered on the aircraft velocity vector, display

updates rates, latency, range resolution, sensitivity, dynamic range, and azimuth and elevation 

resolution. For an active infrared thermal imaging sensor, the infrared illuminator has the 

potential to illuminate more weather obscurations, which can compete with scene contrast and 

interpretation. One advantage of millimeter wave radar systems is their general immunity to 

weather obscurations.

3. Unlike the pilot's external view, the enhanced vision image can be a 

monochrome, two-dimensional display. Some, but not all, of the depth cues found in the natural 

view are also found in the imagery. The quality of the enhanced vision image and the level of 

enhanced vision sensor performance depend on the atmospheric and external visible and nonvisible energy source conditions. Gain settings of the sensor, and brightness or contrast settings 

of the HUD, can significantly affect image quality. Certain system characteristics could create 

distracting and confusing display artifacts.

2-2. Synthetic Vision Systems

a. Synthetic vision is a computer-generated image of the external scene topography

from the perspective of the flight deck that is derived from aircraft attitude, high-precision 

navigation solution, and database of terrain, obstacles, and relevant cultural features. A synthetic 

vision system is an electronic means to display a synthetic vision image of the external scene 

topography to the flight crew. Synthetic vision creates an image relative to terrain and airport 

within the limits of the navigation source capabilities (position, altitude, heading, track, and the 

database limitations). SVS provides situation awareness but cannot be used in lieu of natural 

vision. The application of synthetic vision systems is through a primary flight display from the 

perspective of the flight deck (egocentric), or through a secondary flight display from the 

perspective correlating to outside the aircraft (exocentric, like a “bird’s eye” view of a moving 

map display). This AC addresses both perspectives. The elements of an installed SVS are listed 

below, with the SVS diagram shown in Figure 2.

1. Display (includes interface and installation).

2. System interface.

3. Database of terrain and obstacles.
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4. Sources providing the aircraft altitude, attitude, and position.

Visible

External Scene

Energy

Atmosphere

Aircraft Altitude, 

Attitude, Position

Database

Synthetic

Vision

Display Processing

Pilot's Eye

Display 

Figure 2. Synthetic Vision Diagram

(Dashed lines represent individual system boundaries. External scene visible image is not 

affected by SVS.)

b. Synthetic vision coordinate referenced databases are usually referenced to digital 

terrain elevation data (DTED). Digital terrain data can help produce a digital elevation model 

(DEM), a terrain database used to draw the terrain image on a synthetic vision display.

Note: For information purposes, there are three DTED levels with the following 

terrain spacing:

1. DTED Level 0 uses 30 arc second spacing (nominally one kilometer).

2. DTED Level 1 uses 3 arc second spacing (approximately 100 meters).

3. DTED Level 2 uses one arc second spacing (approximately 30 meters).
MM/DD/YYYY AC 20-167A

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c. With the exception of terrain and database processing (addressed in chapter 4, 

paragraph 4-3.g.), synthetic vision characteristics may include:

1. Display factors, such as:

(a) Conformality.

(b) Refresh rate.

(c) Field of regard (FOR). 

(d) Field of view (FOV).

2. Display placement factors, such as:

(a) Pilot’s primary FOV versus pilot’s secondary FOV.

(b) Head down display (HDD) versus Head up display (HUD). 

3. Terrain presentation factors, such as:

(a) Depiction (such as monochromatic, photo-realistic, elevation 

coloring).

(b) Gridding (presence versus absence, spacing).

(c) Color, shading, shadowing, and texturing. (This AC does not 

establish criteria for these items.)

(d) Resolution. DEM resolution and DTED level.

(e) Range indication (e.g., terrain based range marks, color scheme).

4. Terrain and cultural features, such as:

(a) Rivers, valleys, and mountains.

(b) Major landmarks, highways, and buildings within close proximity

to airport.

(c) Hue and contrast between terrain and sky.

(d) Man-made obstacles (e.g., radio towers, bridges, tall buildings) and 

airport depiction.

(e) Airport depiction, including markings (e.g., extended runway

centerline and numbers, taxiway markings, approach lighting system).

(f) Range marks or indications.

5. Functions, such as:

(a) Alerting (terrain, obstacles, traffic, and airspace).

(b) Declutter.

(c) Mode reversion.

(d) Image control (FOV, brightness, contrast, registration).

6. Integration of guidance symbology (if incorporated), such as:
MM/DD/YYYY AC 20-167A

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(a) Guidance cues (flight path vector, flight path angle reference cue, 

velocity vector, command guidance cues, deviation indicators, and trend 

indicators).

(b) Aircraft reference relative to terrain (indication of relationship 

between zero pitch line and terrain).

(c) Pathway markings (“breadcrumbs,” rectangles) and boundaries, to 

indicate past or intended future aircraft track.

(d) Navigation information (course lines, fixes, icons, special-use 

airspace).

(e) Unusual attitude recovery.

(f) Crosswind indication (and image display based on cross-track).

2-3. Combined Vision Systems

a. The CVS concept involves a combination of SVS and EVS or EFVS. Some 

examples of a CVS include database-driven synthetic vision images combined with real-time 

sensor images superimposed and correlated on the same display. This includes selective 

blending of the two technologies based on the intended function of the vision system for which 

approval is sought. For example, on an approach, most of the arrival would utilize the SVS 

picture. As the aircraft nears the runway, the picture gradually and smoothly transitions from 

synthetic to enhanced vision, either for SVS picture validation or displaying the runway

environment. 

b. For combined vision systems applicants are expected to meet applicable 

performance criteria for each incorporated system.

2-4. Enhanced Flight Vision Systems

a. An EFVS, as defined in 14 CFR 1.1, is “...an installed aircraft system which uses 

an electronic means to provide a display of the forward external scene topography (the applicable 

natural or manmade features of a place or region especially in a way to show their relative 

positions and elevation) through the use of imaging sensors, such as forward-looking infrared, 

millimeter wave radiometry, millimeter wave radar, or low-light level image intensification. The 

EFVS sensor imagery and required aircraft flight information and flight symbology is displayed 

on a head-up display, or an equivalent display, so that the imagery and symbology is clearly 

visible to the pilot flying in his or her normal position with the line of vision looking forward 

along the flight path. An EFVS includes the display element, sensors, computers and power 

supplies, indications, and controls.” During an instrument approach, the enhanced vision image 

is intended to enhance the pilot's ability to detect and identify the visual references required by 

the regulations.

b. An EFVS requires a real-time imaging sensor providing demonstrated vision 

performance in low visibility conditions and a level of safety suitable for the proposed 

operational procedure. This allows the required visual references to become visible in the image 

before they are visible naturally out-the-window. Depending on atmospheric conditions and the 

strength of energy emitted and/or reflected from the scene, the pilot can use the imagery
MM/DD/YYYY AC 20-167A

8

produced by an EFVS to see these visual references on the display better than the pilot can see 

them through the window without enhanced vision. Currently approved enhanced flight vision 

systems use passive infrared sensor technology. However, an active or passive sensor, as 

described in chapter 2, paragraph 2-1.b., could be used provided it meets the performance criteria

in this AC.

c. The basic elements of an installed EFVS are defined in 14 CFR 91.176, and are 

listed below, with the EFVS diagram in Figure 1. Specific system criteria for EFVS systems can 

be found in Section 4 of this AC.

1. An electronic means to provide a display of the forward external scene 

topography (the natural or manmade features of a place or region especially in a way to show 

their relative positions and elevation) through the use of imaging sensors, such as a forwardlooking infrared, millimeter wave radiometry, millimeter wave radar, and low-light level image 

intensifying;

2. The EFVS sensor imagery and aircraft flight symbology (i.e., at least 

airspeed, vertical speed, aircraft attitude, heading, altitude, command guidance as appropriate for 

the approach to be flown, path deviation indications, flight path vector, and flight path angle 

reference cue) are presented on a head-up display, or an equivalent display, so they are clearly 

visible to the pilot flying in his or her normal position and line of vision and looking forward 

along the flight path, to include:

(a) The displayed EFVS imagery, attitude symbology, flight path 

vector, and flight path angle reference cue, and other cues, which are referenced to this imagery

and external scene topography, must be presented so they are aligned with and scaled to the 

external view;

(b) The flight path angle reference cue must be displayed with the 

pitch scale, selectable by the pilot to the desired descent angle for the approach, and suitable for 

monitoring the vertical flight path of the aircraft on approaches without vertical guidance; and

(c) The displayed imagery and aircraft flight symbology do not 

adversely obscure the pilot's outside view or field of view through the cockpit window.

3. The EFVS includes the display element, sensors, computers and power 

supplies, indications, and controls. It may receive inputs from an airborne navigation system or 

flight guidance system; and

4. The display characteristics and dynamics are suitable for manual control 

of the aircraft.

5. Depending on the EFVS intended function, installations designed to be 

eligible for EFVS II operations also need a flare cue and radio altitude. Refer to the performance 

criteria in paragraph 4-5 of this AC.

d. Enhanced flight vision technology can use either stroke or raster technology.

1. Stroke symbology illuminates a small fraction of the total display area of 

the HUD, leaving much of that area free of reflected light that could interfere with the pilot's 

view out the window through the display.
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2. The raster infrared image is in the center of the pilot's regulated "pilot 

compartment view." A "raster" image is comprised of a set of horizontal lines continuously

sweeping across the display to form a picture by modulating their intensity (luminance). It 

should be free of interference, distortion, and glare that would adversely affect the performance 

of the pilot's normal performance and workload. A raster image can be more difficult for the 

pilot to see through than stroke-written symbols also displayed on the HUD. Unlike stroke 

symbology, the raster image illuminates, to some degree, most of the total display area of the 

HUD with much greater potential interference with the pilot compartment view. It is sufficient 

for the pilot to see around the raster image, but the outside scene must be visible through it.

e. Unlike the pilot's external view, the enhanced flight vision image is a 

monochrome, two-dimensional display. Some, but not all, of the depth cues found in the natural 

view are also found in the imagery. The quality of the enhanced flight vision image and the level 

of enhanced flight vision sensor performance could depend significantly on the atmospheric and 

external light source conditions. Gain settings of the sensor, and brightness or contrast settings 

of the HUD, can significantly affect image quality. Certain system characteristics could create 

distracting and confusing display artifacts. Finally, this is a sensor-based system that is intended 

to provide a conformal perspective. Refer to Figure 1 for a diagram of the system.

f. Depending on the intended operational function of the EFVS, airworthiness 

approval will be designated as an EFVS I or EFVS II as described below. Depending on the 

airworthiness approval being sought by the applicant, additional basic equipage may be required. 

Those additional requirements can be found in paragraph 4-5 of this AC.

1. EFVS I – The installed EFVS has been demonstrated to meet the criteria 

for AC 20-167A for EFVS I to be used for instrument approach operations from DA/DH or 

MDA to 100 HAT. 

2. EFVS II – The installed EFVS has been demonstrated to meet the criteria 

for AC 20-167A for EFVS II to be used for instrument approach and landing operations that rely 

on sufficient visibility conditions to enable unaided rollout and to mitigate for loss of EFVS 

function. An EFVS that meets the certification criteria for EFVS II also meets the certification 

criteria for EFVS I. Flight Standards currently authorizes EFVS II operations to be conducted on 

a straight-in instrument approach procedure from DA/DH to touchdown to visibilities as low as a 

Runway Visual Range (RVR) of 1000 feet, depending on what was demonstrated during 

certification flight test.

g. Although the European Aviation Safety Agency (EASA) uses the term “EVS” as 

equivalent to the FAA “EFVS,” do not confuse an EFVS with an Enhanced Vision System 

(EVS).

1. Unlike with EFVS, an aircraft with EVS does not necessarily provide the 

additional flight information or symbology required by 14 CFR 91.176. An EVS is not required 

to use a HUD, and may not be able to present the image and flight symbology in the same scale 

and alignment as the outside view. An EVS can provide situation awareness to the pilot, but 

does not meet the regulatory requirements of 14 CFR 91.176. An EVS cannot be used as a 

means to determine enhanced flight visibility or to identify the required visual references in order 

to gain operational credit and descend below the DA/DH or MDA.
MM/DD/YYYY AC 20-167A

10

2. For the primary display, the regulations also make provision for an 

equivalent display. Specifically, 14 CFR 91.176(a),(1),(i),(B) states that the EFVS sensor 

imagery and aircraft flight symbology must be presented “ on a head-up display, or an equivalent 

display, on which the imagery and symbology is clearly visible to the pilot flying in his or her 

normal position with the line of vision looking forward along the flight path.” An equivalent 

display must be some type of head-up presentation of the required information. A head-down 

display does not meet the regulatory requirement. For the monitoring display, see paragraph 4-

5.b.(1) of this AC.
MM/DD/YYYY AC 20-167A

11

Chapter 3. Airworthiness Package Contents

3-1. Airworthiness Package

The applicant is responsible for the following contents in the airworthiness package (for the 

purpose of this AC). This AC specifically addresses SVS with attitude displayed on the primary 

flight display (PFD), EVS/SVS/CVS with a head down display other than a PFD (such as a 

navigation display or multifunction display), EVS image displayed on a head up display, and an 

EFVS. 

a. Intended function: Information on intended function can be found in section 3-2.

b. General operation: Information on the general operations and specific 

performance criteria can be found in Chapter 4.

c. Performance criteria and evaluation plan for the respective system. Performance 

evaluation is addressed in Chapter 6 with sample test considerations found in the appendices of 

this document, and

d. Installation considerations: Information regarding installation considerations can 

be found in Chapter 5 of this document.

Note: Depending on the system (for example, EVS, SVS, CVS, or EFVS), the 

appropriate guidance will depend on the respective system.

3-2. Intended Function.

a. EVS, SVS, or CVS: Define the intended functions of your EVS, SVS or CVS. 

Include what features you will display and the criticality of pilot decision-making using the 

display features. Define additional intended functions (for example, terrain alerting) according 

to AC 25-11A and 14 CFR 2X.1301.

b. EFVS: Clearly define the intended function of your EFVS (EFVS I, II, or III). 

This must include its use to assess enhanced flight visibility and to visually acquire the visual 

references required to operate below the DA/DH or MDA as specified in 14 CFR 91.176 (a) and 

(b), 121.651, 125.381 and 135.225, and the criticality of pilot decision-making based on what is 

visible using the EFVS display. The purpose of the EFVS is to provide a visual advantage over 

the pilot’s out-the-window view using natural vision. In low visibility conditions, the “enhanced 

flight visibility” should exceed the “flight visibility” and the required visual references should 

become visible to the pilot at a longer distance with an EFVS than they would out-the-window 

using natural vision. Visual advantage using an EFVS must be demonstrated before descending 

below DA/DH or MDA because this is the point in an instrument approach procedure where the 

operating rules permit an EFVS to be used in lieu of natural vision for operational benefit.

Note 1: The EFVS is not intended to change the technologies or procedures already used 

to safely fly the aircraft down to the MDA/MDH or DA/DH. The EFVS sensor provides a visual 

advantage over the pilot's out-the-window view. In low visibility conditions, the "enhanced 

flight visibility" should exceed the "flight visibility" and the required visual references should 

become visible to the pilot at a longer distance in the EFVS than out-the-window. The EFVS 
MM/DD/YYYY AC 20-167A

12

complements other instrument approach equipment by providing a means for the pilot to see 

(with the EFVS) the required visual references that might otherwise not be visible

Note 2: While the goal of EFVS is to exceed the natural flight visibility in the majority

of cases/weather conditions, there may be meteorological conditions where the EFVS does not 

provide a significant advantage.
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13

Chapter 4 System Criteria

4-1. EVS or SVS (or CVS when EVS and SVS combined) – General.

a. EVS/SVS/CVS Primary Displays. EVS, SVS, or CVS functionality can be 

superimposed on the electronic flight instrument system (EFIS), for example the primary flight 

display (PFD) as installed in the flight deck. In this configuration example, the EVS, SVS, or 

CVS image can be merged into the sky/ground shading of the attitude direction indicator. In 

addition to the traditional head down display PFD, this type of superimposed display could also 

be associated with a HUD or equivalent display system using EVS, SVS, or CVS capabilities.

Maneuvering the aircraft during any phase of flight (taxi, approach, landing rollout, etc.) shall 

not be predicated on EVS imagery.

b. EVS/SVS/CVS Secondary Displays. EVS, SVS, or CVS functionality can be 

selected on a multi-function display (MFD) or navigation display (ND) as one of many standalone type formats available in the flight deck. For example, an EVS, SVS, or CVS image can 

be one selection on the MFD, while an electrical synoptic could be another selection on the same 

MFD.

c. EVS, SVS, or CVS installed on side-mounted displays: While similar in concept 

to the MFD, side-mounted displays systems are, in general, limited due to the nature of the 

installation constraints of these devices. Side-mounted displays of EVS technologies can present 

unique certification challenges such as alignment or positioning concerns relating to the display

installation. (See AC 120-76B, Guidelines for Certification, Airworthiness, and Operational Use 

of Electronic Flight Bag, for specific applications.)

d. The intended function for any installation of EVS/SVS/CVS must be clearly 

defined (appropriate 14 CFR 2X.1301), and the design and installation safety levels must be 

appropriate for the stated intended function. Although normally associated with use during 

flight, utilization of EVS display during ground operations should not be used if sensor 

proximity to the taxiway surface causes a distraction.

1. The intended function should be reasonable considering the actual 

functionality of the installation.

2. Operating limitations should be proposed to the FAA by the applicant. 

Operating limitations must be clearly defined and stated in the aircraft’s flight manual 

supplement in line with the intended function.

3. An EVS must not be used for flight guidance or navigation. An EVS 

cannot be used in lieu of natural vision to descend below DA/DH or MDA under 91.176, 

121.651, 125.381 or 135.225 regardless of whether it is on a HUD, or on a head down display.

e. Although EVS/SVS/CVS installations do not provide additional operational 

credit, the proposed system (EVS, SVS, and/or CVS):

1. Should have a means to automatically or manually control display

brightness.

2. Must not degrade presentation of essential flight information. In other 

words, the pilot’s ability to see and use the required primary flight display information such as 
MM/DD/YYYY AC 20-167A

14

primary attitude, airspeed, altitude, and command bars/command guidance must not be hindered 

or compromised by the EVS/SVS/CVS image.

3. If the vision system uses a head-up display or the equivalent, then it may

not distort the pilot compartment view, provide a distorted (i.e. non-conformal) view of the 

external scene, or interfere with the pilot’s ability to safely perform any maneuvers within the 

operating limitations of the aircraft, including taxiing, takeoff, approach, and landing. See 

paragraph 4-1.f.2 of this section. 

4. Not adversely affect any other installed aircraft system.

5. Perform its intended function in each aircraft environment where system 

approval is desired. For example, if the system is intended to perform in (or after exposure to) 

known icing conditions, a means can be required to keep the EVS sensor window clear of ice 

accumulation.

6. Display the mode of operation (EVS, SVS, or CVS) to the pilot/crew. 

Consideration should be given to recording the EVS/SVS/CVS display status in a flight data 

recorder or some form of nonvolatile memory.

7. Not have undesirable display characteristics (for example, jitter, jerky

motion, and excessive delays).

f. Display Implementation. EVS/SVS/CVS can be incorporated into differing 

display types installed in the cockpit. AC 25-11A and AC 23.1311-1C, Installation of Electronic 

Display in Part 23 Airplanes, provide more information on electronic displays. The display is 

subject to all applicable primary flight information rules and guidance for the category of 

aircraft.

1. Primary Flight Display (PFD). Primary displays are cockpit displays used 

to provide information needed to guide and control the aircraft and provide the aircraft altitude, 

attitude, and airspeed indications. EVS/SVS/CVS can be implemented on the primary Head 

Down Display (HDD) in 14 CFR part 23 and 25 aircraft. Refer to AC 27-1B and AC 29-2C for 

guidance on installation on rotorcraft. The following criteria apply to EVS/SVS/CVS 

implemented on a PFD.

(a) The image, or loss thereof, must not adversely affect the PFD 

functionality.

(b) Align the displayed image with the aircraft’s inertial axis, physical 

axis or as appropriate for the intended function. The alignment can be variable and/or “phase of 

flight” dependent. The relationship between the image and the aircraft’s heading angle, pitch 

angle, roll angle, and track angle should generally align with the trajectory of the aircraft, should 

be recognizable by the flight crew, and not be misleading. For example, if two displays show 

EVS, SVS, or CVS information, or a combination (EVS on one and SVS on another), the 

orientation of the displays should be the same. Alignment of imagery presented on the PFD 

should be consistent with the real world and appropriate for the system’s intended function 

accounting for possible aircraft attitudes, turbulence, and wind effects.

(c) Scale and align all spatially referenced symbology within each axis 

with the imagery so as not to present any misleading information to the pilot.
MM/DD/YYYY AC 20-167A

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(d) The Field of Regard (FOR) can be variable, but must be designed 

to ensure the displayed image is not distracting or misleading and does not adversely affect crew 

performance and workload. (reference 14 CFR §§ 2X.771 and 2X.1309.)

(e) The display should not impede a clearly visible zero pitch 

reference line, distinct in visual appearance relative to any possible terrain, obstacle, or cultural 

feature display appearance.

Note: Consider including a flight path vector or velocity vector to show 

the pilot the aircraft’s trajectory relative to displayed terrain.

(f) Per 14 CFR 2x.771 and 2x.773, pilot tasks must not be degraded 

by the displayed imagery. Depending on the intended function of the display information, the 

imagery must not provide the pilot with misleading information regarding detection, accurate 

identification, and avoidance of terrain, obstacles, and other flight hazards.

2. Head-Up Display. EVS/SVS/CVS can be implemented on a HUD, HDD 

or equivalent. The following criteria apply to EVS/SVS/CVS implemented on a HUD display:

(a) A design with EVS/SVS/CVS imagery displayed on a HUD must 

account for the pilot compartment view requirements found in 14 CFR 23.773, 25.773, 27.773, 

and 29.773, including validation that the display of EVS imagery does not conflict with the pilot 

compartment view. The following tasks associated with the use of the pilot’s view must not be 

degraded below the level of safety that existed without the EVS:

(i) Detection, accurate identification and maneuvering, as 

necessary, to avoid traffic, terrain, obstacles, and other hazards of flight.

(ii) Accurate identification and utilization of visual references 

required for every task relevant to the phase of flight.

Note: Although normally associated with use during flight, 

utilization of video imagery on the HUD during ground operations should not be considered if 

sensor proximity to the taxiway surface causes a distraction.

(b) The safety and performance of the pilot tasks associated with the 

use of the pilot compartment view must not be degraded by the display of imagery on the HUD. 

Per 14 CFR 2X.773, pilot tasks which must not be degraded by the imagery include:

(i) Detection, accurate identification, and maneuvering, as 

necessary, to avoid traffic, terrain, obstacles, and other hazards of flight.

(ii) Accurate identification and utilization of visual references 

required for every task relevant to the phase of flight.

(c) Imagery on the HUD must be conformal with the real world and 

appropriate for the system’s intended function accounting for possible aircraft attitudes, 

turbulence, and wind effects.

(d) Society of Automotive Engineers (SAE) International design 

standards for HUD symbology, optical elements and video imagery are also prescribed with SAE 

Aerospace Standard (AS) 8055, Minimum Performance Standard for Airborne Head Up Display

(HUD), dated March 1999, SAE Aerospace Recommended Practice (ARP) 5288, Transport 

Category Airplane Head Up Display (HUD) Systems, dated May 2001, and SAE ARP 5287, 
MM/DD/YYYY AC 20-167A

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Optical Measurement Procedures for Airborne Head Up Display (HUD), dated March 1999. 

Apply specific design standards for resolution and line width, luminance and contrast ratio, 

chromaticity, and grayscale.

3. Secondary displays. EVS/SVS/CVS can be implemented with ego-centric 

“inside aircraft” views or exocentric “outside aircraft” viewpoints on head down displays. This 

includes installed EFBs or MFD. The following criteria apply to EVS/SVS/CVS implemented 

on secondary displays:

(a) The orientation and perspective of the EVS/SVS/CVS view should

be clear to the pilot.

(b) If PFD information is displayed, it should meet PFD integrity 

requirements and availability criteria.

(c) EVS/SVS/CVS image, or loss thereof, must not adversely affect 

other approved display functionality (such as navigation displays).

Note: Generally, the orientation of the secondary display should be the 

same as the primary display to decrease the possibility of pilot confusion.

4-2. EVS Specific Criteria.

a. An EVS requires a real-time imaging sensor and display, providing improved 

vision performance. These systems do not qualify for additional operational credit over and 

above what is already approved, and are installed on a non-interference basis.

b. EVS installations must meet the following criteria:

1. The EVS depiction must be crew de-selectable (if on the primary display, 

the pilot should be able to easily and quickly declutter the EVS or remove sensor image). For an 

EVS image displayed on a HUD, provide a control which permits the pilot flying to deactivate 

and reactivate the display of the EVS image on demand without removing the pilot’s hands from 

the primary flight controls (yoke or equivalent) or thrust control.

2. The display mode (status of EVS), either through crew de-selection or as a 

result of a failure, should be clearly indicated or obvious to the crew.

3. The display and sensor FOR should be sufficient for the intended 

functions.

4. SAE design standards for EVS symbology, optical elements and video 

imagery are also prescribed in SAE AS 8055, SAE ARP 5288 and SAE ARP 5287. Apply the 

specific design standards for resolution and line width, luminance and contrast ratio, 

chromaticity, and grayscale.

5. Consider the following criteria for display characteristics for the EVS 

design, regardless of the display type:

(a) For part 25 airplanes, apply all display characteristics listed in AC 

25-11A. For part 23 airplanes, apply all display characteristics listed in AC 23.1311-1. For 

other aircraft without corresponding criteria, the guidance in AC 25-11A or AC 23.1311-1 serves 

as recommended guidance.
MM/DD/YYYY AC 20-167A

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(b) The display should not have undesirable display characteristics 

(such as blooming, “burlap,” and running water).

6. Image characteristics.

(a) On a HDD, the relationship of the display FOR to the actual field 

of view should be suitable for the pilot to smoothly transition from the HDD to the out-thewindow real world view or HUD.

(b) The image data should be refreshed at 15 Hz or better.

(c) The image latency should be less than 100 milliseconds where the 

latency is measured from the image source time of applicability to the display of the image.

Note: EVS refresh rate, when used in direct aircraft or power plant 

manual control tasks (such as attitude, engine parameters, etc.), equal to, or greater than 15 Hz 

has been found to be acceptable. Any lag introduced by the display system should be consistent 

with the aircraft control task associated with that parameter. In particular, display system lag 

(including the sensor) for attitude which does not exceed a first order equivalent time constant of 

100 milliseconds for aircraft with conventional control system response is generally acceptable.

7. For display on a HUD, the minimum system should provide a control of 

the EVS display contrast/brightness which is effective in dynamically changing background 

(ambient) lighting. In addition, the minimum system must:

,

(a) prevent distractions to the pilot, 

(b) Prevent impairment of the pilot’s ability to detect and identify

visual references,

(c) Prevent masking of flight hazards, 

(d) Prevent degradation of task performance or safety.

8. When EFVS is incorporated on the primary display, the EVS-based 

primary display must be clear and unambiguous when recovery from unusual attitudes is 

required. An accurate, easy, quick-glance interpretation of attitude should be possible for all 

unusual attitude situations and other “non-normal” maneuvers sufficient to permit the pilot to 

recognize the unusual attitude and initiate a recovery within one second. We recommend you 

use chevrons, pointers, and/or permanent ground-sky horizon on all attitude indications to 

perform effective manual recovery from unusual attitudes. (For part 25 aircraft, refer to AC 25-

11A. For part 23 aircraft, refer to appendix 8.) Always have some indication of both sky and 

ground visible on the PFD for use in initiating unusual attitude recovery. 

4-3. SVS Specific Criteria.

a. Synthetic Vision Systems require a terrain and obstacle database, a precision 

navigation position, display, and height, attitude, and heading/track inputs. The design and 

installation safety levels should be appropriate for the system’s intended function. AC 25-11A 

and AC 23.1311-1 provide additional general display guidance.

b. Image characteristics:
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1. Failure or de-selection of the synthetic vision depiction should be obvious 

to the crew.

2. The display can depict the scene from the pilot’s view looking through the 

front window (egocentric) or from outside the aircraft (exocentric). However, if implemented on 

a primary display, then the display should depict the scene from the pilot’s perspective looking 

through the front window.

3. The Field of Regard (FOR) should be appropriate for the system’s 

intended function and account for possible aircraft attitudes, turbulence, and wind effects (for 

example, to orient the line of sight according to heading and not to track). Synthetic vision scene 

compression can result from FOR selections or display size limitations. Regardless, prominent 

topographical features should be easily identified and must be correlated with the actual external 

scene.

4. Identify dominant topographical features present in the SVS image in the 

outside view. Dominant topographical features present in the outside view should also be 

identifiable in the SVS image.

5. Terrain:

(a) A potential terrain or obstacle conflict should be obvious to the 

pilot, and must not conflict with TAWS or HTAWS requirements. One mechanism for making 

such conflicts obvious on a primary display is an earth-based flight path vector. For guidance

regarding alerts, use AC 23.1311-1 or AC 25.1322-1.

(b) Displayed topographical features should not intersect guidance 

provided to the pilot to fly a published approach path. Terrain and 3-space position resolution 

should be accurate enough that topographical features should not intersect published approach 

paths.

(c) Threatening terrain, close enough to generate a terrain warning 

alert, should appear above the artificial horizon zero pitch reference line if it is higher than the 

aircraft altitude.

6. SVS-based primary displays must be clear and unambiguous when 

recovery from unusual attitudes is required. An accurate, easy, quick-glance interpretation of 

attitude should be possible for all unusual attitude situations and other “non-normal” maneuvers 

sufficient to permit the pilot to recognize the unusual attitude and initiate a recovery within one 

second. We recommend you use chevrons, pointers, and/or permanent ground-sky horizon on all 

attitude indications to perform effective manual recovery from unusual attitudes. (For part 25 

aircraft, refer to AC 25-11A. For part 23 aircraft, refer to appendix 7.) Always have some 

indication of both sky and ground visible on the PFD for use in initiating unusual attitude 

recovery. SVS displays used as an attitude indicator require an egocentric orientation.

7. The relationship of the display FOR to the actual field of view should be 

suitable for the pilot to smoothly transition from the head-down display to the head-up, out-thewindow real features.

8. The terrain depiction should include large bodies of water and rivers. 

Differentiation between water and sky depictions should be clearly distinguishable.

9. The pilot’s view should not be depicted below the earth’s surface.
MM/DD/YYYY AC 20-167A

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10. The image should be updated at 15 Hz or better and function smoothly

during all expected maneuvering reasonable for the class and type of aircraft.

11. The image latency for a PFD or HUD should be consistent with the image 

guidance in AC 25-11A or that necessary for expected maneuvering reasonable for the class and 

type of aircraft. For other displays in the flight deck, a larger lag can be acceptable subject to the 

intended function.

12. Undesirable display characteristics should be minimized (for example, 

jitter, jerky motion, and excessive delays).

13. Range:

(a) The scene range should be the natural horizon for both egocentric 

and exocentric displays. For systems intended for use in approach, missed approach, take-off, 

and departure operations, the scene range should be whichever is less of the following: natural 

horizon, 40 nautical miles, or 10 minutes at maximum cruise speed.

(b) The scene range from the eye position to the terrain horizon must 

not be misleading and must be appropriate to the intended function. The intent is to prevent 

misleading information due to a SVS range limitation to the horizon that could lead to crew 

confusion at a critical phase of flight. At some airports the missed approach can take the aircraft 

on a course towards mountains. Pilots need to see that the mountains will be a factor in their

missed approach long before they get to the runway. Thus, it is not acceptable for an approach to 

appear as if it is over flat terrain until short final when the mountains in the distance finally start 

appearing on the PFD.

14. Although every possible scenario cannot be described, the crew should be 

able to perceive relative distances to prominent topographical features. For example, the pilot 

should be able to identify an immediate terrain threat versus a distant terrain conflict.

15. All obstacles taller than 200 feet above ground level should be displayed. 

These obstacles must be displayed conformally on the synthetic vision image.

Note: Obstacle display consideration should be given to reducing clutter 

when objects pose no threat, yet not suddenly appear at low altitudes during periods of task 

saturation.

c. Position Source. The horizontal position source used for the SVS display should 

at least meet the criteria for TAWS or HTAWS. The horizontal position source must not provide 

contradictory indications of horizontal terrain clearance. Additional guidance for the horizontal 

position source can be necessary, depending on the intended functions of the SVS. TAWS 

guidance is contained in AC 25-23 and AC 23-18. HTAWS guidance is contained in AC 27-1B 

and 29-2C.

1. The synthetic vision display must not conflict with either the terrain 

warning or terrain awareness functions (for example, TAWS or HTAWS).

2. Any aircraft incorporating SVS from the egocentric perspective should

also provide a TAWS or HTAWS or terrain warning system (refer to appendix 8 for specifics on 

a terrain warning system). If terrain alerts and cautions are depicted on the SVS, they must be 

consistent across all displays in the cockpit when terrain threats are identified. In other words, 

terrain database sources should be consistent.
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d. Altitude Source. The altitude source used for the SVS display should meet the 

criteria for TAWS or HTAWS installations, including the need to account for cold temperature 

errors which could place the aircraft closer to the surface than the altimeter indicates. The 

altitude source should be consistent with that used for the onboard terrain awareness and alerting 

system on the aircraft and must not provide contradictory indications of vertical terrain 

clearance. Additional criteria for the altitude source can be necessary, depending on the intended 

functions of the SVS. TAWS guidance is contained in AC 25-23 and AC 23-18. HTAWS 

guidance is contained in AC 27-1B, AC 29-2C, and TSO-C194.

e. Attitude Source. The attitude source must not conflict with attitude information 

or integrity criteria provided by the primary flight display.

f. Heading/Track Source. The heading/track source must not conflict with 

heading/track information provided by the navigation display.

g. Terrain and Obstacle Database.

1. Terrain and obstacle database processing. The terrain and obstacle 

database, along with any other database used to create the SVS image should be compliant to 

RTCA/DO-200A, as applicable to the intended function. The minimum terrain database 

resolution and accuracy must be consistent with the intended function, and should comply with 

the resolution and accuracy listed in TSO-C151, appendix 1, section 6.3, or for helicopters, TSOC194.

(a) Position accuracy, symbology, and topographical information 

should be consistent with each other.

(b) Runway elevations must be accurate at the approach ends and not 

just at the airport center.

2. Obstacle database. The obstacle database should include all available 

physical hazards greater than 200 feet above ground level, not just terrain. The system should

neither disregard nor corrupt obstacles available in the database greater than 200 feet above 

ground level. Obstacles displayed should be those deemed hazardous to the flight (or phase of 

flight). The applicant should provide procedures in the Instructions for Continued Airworthiness 

to ensure the most current obstacle database is installed.

Note: It is difficult to apply one altitude value across a wide range of aircraft 

performance, from rotary wing to high performance fixed wing. Generally, above 5,000 ft AGL, 

most obstacles are not tall enough to be hazardous. However, in the airport terminal area, even 

obstacles less than 1,000 ft AGL can be hazardous.

3. Navigation Database. The navigation database used by SVS for runway

and airport information should be consistent with that used by other systems in the aircraft (for 

example, flight management systems). The applicant should provide procedures to document 

database currency in the Instructions for Continued Airworthiness.

4. Features. If flight path guidance features are provided by the SVS, they

should complement (or correspond with) approved navigation system guidance.

5. Head-Up Displays. Providing complete guidance for synthetic vision 

systems is complicated by the many design variables available to manufacturers. Since synthetic 
MM/DD/YYYY AC 20-167A

21

vision displays can share many characteristics with a HUD, applicants should use HUD display

guidance where appropriate.

6. Terrain display. If the intended function is “terrain awareness,” then 

“awareness” is consistent with the actual terrain. The display may not match the terrain perfectly, 

but the display should provide a reasonable representation of the terrain in a manner that does not 

misrepresent the threat posed by the terrain. The display, while possibly resolution or field-ofview limited, may still adequately portray terrain awareness. The pilot should be aware of less 

than a 1:1 ratio of depiction. Display suitability must be matched against intended function.

4-4. CVS Specific Criteria.

a. CVS requires a real-time imaging sensor and display that provides demonstrated 

vision performance for its intended function. They also require a terrain and obstacle database 

and a precision navigation position for the synthetic portion of the display. The design assurance 

levels should be appropriate for the system’s intended function. The following criteria apply to 

CVS installations:

1. CVS should meet the respective criteria of the EVS and SVS 

implementations.

2. The EVS and SVS depictions should be conformal with each other.

3. Fusion of EVS and SVS should require the images to be aligned within 5 

milliradian (mrad) laterally and vertically at the boresight of the display. Therefore, blended 

EVS and SVS images should not cause confusion to the flight crew. Image discrepancies 

between EVS and SVS due to failure conditions should be obvious to the crew.

Note: It is difficult to define every implementation in order to determine what is 

“significant.” However, the applicant is expected to reduce discrepancies to as 

near-zero as possible. The final determination will occur during flight test.

b. The CVS should meet the detailed performance criteria for EVS and SVS 

specified in paragraphs 4-2 and 4-3 of this chapter.

4-5. EFVS – General and Specific Criteria.

a. EFVS criteria would meet EVS criteria. However, there are additional EFVS 

general and specific criteria needed to be eligible for operational credit, as follows:

1. Mitigate system failures more frequent than extremely improbable which 

produce effects the pilot (or the aircraft itself) cannot safely handle. Design the aircraft systems 

so the entire fault probability is kept to an acceptable level, and complies with 14 CFR part 

2x.1309 regulations.

2. The sensor image, combined with the required aircraft state and position 

reference symbology, is presented to the flight crew on the HUD, or an equivalent display, so 

that they are clearly visible to the pilot flying in his or her normal position and line of vision 

looking forward along the flight. For HUD operations, the pilot flying views the EFVS sensor 

and symbolic information that is properly aligned and registered to enable a one-to-one 

(conformal) overlay with the actual external scene.
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3. The HUD and displayed FOR should be sufficient for the EFVS 

information to be displayed conformally over the range of anticipated aircraft attitudes, aircraft 

configurations, and environmental (for example, wind) conditions. The aircraft state and 

position reference data is presented in the form of symbology overlaying the image presentation. 

The flight instrument data on the HUD must include:

(a) Airspeed;

(b) Vertical speed;

(c) Aircraft attitude;

(d) Heading;

(e) Altitude;

(f) Command guidance as appropriate for the approach to be flown

(g) Path deviation indications

(h) Flight path vector; and

(i) Flight path angle reference cue.

4. For an EFVS II intended for landing and rollout (i.e. from DA/DH through

touchdown and roll-out at not less than 1000ft RVR, the following specified aircraft flight 

information, in addition to that noted above in 4-5.a.3, must also be displayed:

(a) Radio altitude, and

(b) Flare prompt or flare guidance for achieving acceptable touchdown 

performance, as required by paragraph 6-2.

5. The minimum system should include a control of EFVS display

contrast/brightness which is effective in dynamically changing background (ambient) lighting, 

prevents distractions to the pilot, prevents impairment of the pilot’s ability to detect and identify

visual references, prevents masking of flight hazards, or otherwise degrades task performance or 

safety. If automatic control for image brightness is not provided, it should be shown that manual 

setting of image brightness meets the above criteria and does not cause excessive workload.

6. The EFVS display controls should be visible to, and within reach of, the 

pilot flying from any normal seated position. The position and movement of the controls should

not lead to inadvertent operation. The EFVS controls, except those located on the pilot’s control 

wheel, should be adequately illuminated for all normal background lighting conditions, and 

should not create any objectionable reflections on the HUD or other flight instruments. Unless 

fixed illumination of the EFVS controls is shown to be satisfactory under all lighting conditions 

for which approval is sought, there must be a readily accessible control provided that permits the 

pilot to immediately deactivate or reactivate the display of the EFVS image on a HUD. This 

control must be on demand without removing the pilot’s hands from the primary flight controls 

(yoke or equivalent) and thrust control.

7. Base the approach path situation information references and command 

guidance information on the navaids dictated by the straight-in instrument approach procedure in 

use.
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8. Under FAA regulations, as defined in 14 CFR 91.176, upon reaching the 

decision altitude/decision height (DA/DH) or minimum descent altitude/minimum descent height 

(MDA/MDH), the required visual references presented in Table 1 must be distinctly visible and 

identifiable to the pilot.

Table 1. 14 CFR 91.176 EFVS Visibility and Visual Reference Requirements

From the authorized DA/DH to 100 feet height above touchdown zone 

elevation of the runway of intended landing, the approach light system (if 

installed) or both the runway threshold and the touchdown zone are distinctly

visible and identifiable to the pilot using an EFVS.

(A)The runway threshold must be identified using at least one of the 

following visual references -

(1) The beginning of the runway landing surface;

(2) The threshold lights; or

(3) The runway end identifier lights.

(B) The touchdown zone must be identified using at least one of the 

following visual references -

(1) The runway touchdown zone landing surface;

(2) The touchdown zone lights;

(3) The touchdown zone markings; or

(4) The runway lights

At 100 feet height above touchdown zone elevation of the runway of 

intended landing the approach can be continued while still relying on the EFVS 

imagery provided that at least one of the following visual references must be 

visible and identifiable to the pilot using an EFVS.

(A)The runway threshold;

(B) The lights of markings of the threshold

(C) The runway touchdown zone landing surface; or 

(D)The lights or markings of the touchdown zone.

9. In terms of sensor design criteria, sensor performance criteria can be 

quantified in terms of the range of the enhanced flight visibility when low visibility conditions 

exist. The visual references of the runway environment must be seen by the sensor at 

operationally relevant distances.

10. The minimum detection EFVS range (figure 3, below) can be derived by 

using an assumed minimum distance of the aircraft at the nominal Category I (200 ft) decision 

altitude before which the EFVS should image the runway threshold. On a 3 degree glide slope, 

the horizontal distance from the aircraft to the runway threshold is approximately 2816 feet 

(3816 feet from the precision touchdown zone markers). Use this range as a minimum 

requirement. These values do not take into account pilot decision time or actual atmospheric 

conditions, the use of non-precision approaches which can require greater distances, or the use of 

approaches with higher DAs, DHs, or MDAs.
MM/DD/YYYY AC 20-167A

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Figure 3. Minimum Detection Range

11. The EFVS imagery displayed on the HUD must account for the pilot 

compartment view requirements found in 14 CFR 25.773, 23.773, 27.773, and 29.773, including 

validation that the display of imagery does not conflict with the pilot compartment view. The 

display of EFVS sensor imagery should be on a system that compensates for the interference 

caused by the provided imagery provides an undistorted and conformal view of the external 

scene, provides a means to deactivate the display and does not restrict the pilot from performing 

specific maneuvers. The following tasks associated with the use of the pilot’s view must not be 

degraded below the level of safety that existed without the video imagery:

(a) Detection, accurate identification and maneuvering, as necessary, 

to avoid traffic, terrain, obstacles, and other hazards of flight.

(b) Accurate identification and utilization of visual references required 

for every task relevant to the phase of flight.

Note: Although normally associated with use during flight, utilization of 

video imagery on the HUD during ground operations should be considered if sensor proximity to 

the taxiway surface causes a distraction.

b. EFVS General System Criteria.

1. The EFVS image must be compatible with the FOV and head motion box 

of a HUD designed against SAE ARP 5288 (transport category head-up display (HUD) systems). 

The HUD and EFVS FOR must provide a conformal image with the visual scene over the range 

of aircraft attitudes and wind conditions for each mode of operation.

(a) A display that provides the pilot monitoring with EFVS sensor 

imagery is not required for EFVS I operations. However, for EFVS II operations, when a 

minimum flightcrew of more than one pilot is required for the conduct of the operation, the 

aircraft must be equipped with an operable display that provides the pilot monitoring with EFVS 

sensor imagery.

(b) The display must be located within the maximum primary field of 

view of the pilot monitoring and any symbology displayed must not adversely obscure the sensor 

imagery of the runway environment.
MM/DD/YYYY AC 20-167A

25

2. EFVS display criteria must meet the airworthiness certification 

requirements in 14 CFR parts 21, 23, 25, 27, and 29 (as applicable). Specifically, the EFVS 

system installation and operations must demonstrate compliance with the requirements listed in 

Appendix 1, EFVS compliance checklist. These requirements are specific to EFVS and are in 

addition to all other requirements applicable to the HUD and the basic avionics installation.

3. The current FAA guidelines for head-up displays apply with respect to 

EFVS. These criteria include well-established military as well as civil aviation standards for 

HUDs as defined in MIL-STD-1787C, Aircraft Display Symbology, and AC 25-11A. SAE 

design standards for HUD symbology, optical elements and video imagery are also prescribed 

within SAE AS 8055, SAE ARP 5288 and SAE ARP 5287. Apply specific design standards for 

image size, resolution and line width, luminance and contrast ratio, chromaticity and grayscale.

4. The EFVS image, when superimposed on the HUD symbology and when 

used in combination with other aircraft systems, must meet the criteria below. The EFVS image 

and installation must:

(a) Be suitable for and successfully perform its intended function.

(b) Allow the accurate identification and utilization of visual 

references, using both EFVS and natural vision as appropriate.

(c) Have acceptable display characteristics to accomplish the intended 

function.

(d) Provide a means to allow the pilot the pilot using the display to 

immediately deactivate and reactivate the vision system imagery, on demand, without removing 

the pilot’s hands from the primary flight controls (yoke or equivalent) or thrust controls.

(e) Not degrade the presentation of essential flight information on the 

HUD.

(f) Not be misleading and should not cause confusion or any 

significant increase in pilot workload.

(g) Be aligned and scaled to the external scene, and should include the 

effect of near distance parallax. 

(h) Not cause unacceptable interference with the safe and effective use 

of the pilot compartment view.

(i) Not significantly alter the color perception of the external scene to 

preclude the pilot’s performance of any required maneuvers.

(j) Allow the pilot to recognize misaligned or non-conformal 

conditions.

5. Additionally, the EFVS installation and image should have an effective 

control of EFVS display brightness without causing excessive pilot workload and not cause 

adverse physiological effects such as fatigue or eyestrain.

6. A HUD modified to display EFVS must continue to meet the conditions of 

the original approval and be adequate for the intended function, in all phases of flight in which 
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26

the EFVS is used. An accurate, easy, quick-glance interpretation of attitude should be possible 

for all unusual attitude situations and other “non-normal” maneuvers to permit the pilot to 

recognize the unusual attitude and initiate recovery within one second. We recommend you use 

chevrons, pointers, and/or permanent ground-sky horizon on all attitude indications to perform 

effective manual recovery from unusual attitudes. Refer to AC 25-11A for guidance on 

electronic flight deck displays.

7. 14 CFR 91.176 requires that the EFVS display a flight path vector (FPV) 

and flight path angle reference cue (FPARC) on the HUD or equivalent display. The following 

criteria apply to these symbols:

(a) The position and motion of the FPV should correspond to the 

aircraft’s earth referenced flight path vector.

(b) The dynamic response of FPV should follow pilot control inputs. 

Refer to AE ARP 5589 for dynamic response guidance.

(c) The display of the FPARC should be suitable for monitoring the 

vertical flight path of the aircraft.

(d) The System should provide the pilot a means to select the desired 

descent angle that is represented by the FPARC.

8. The display of attitude symbology, FPV, FPARC, and other visual 

elements which are earth-referenced, must be aligned with and scaled (i.e., conformal) to the 

external view.

9. The EFVS display of imagery, flight information and flight symbology

should be a suitable visual reference for the pilot during the manual performance of any 

maneuvers within the operating limitations of the aircraft, including taxiing, takeoff, approach, 

landing and rollout.

c. EFVS Detailed System Criteria.

1. The performance of EFVS imaging systems does not solely depend upon 

system design, but also depends upon the target scene characteristics such as the runway, light 

structures, electromagnetic radiation and atmospheric conditions.

2. Since the purpose of the EFVS sensor is to provide a visual advantage 

over the pilot’s out-the-window view, the design should include a general performance analysis. 

This analysis includes calculated performance, which indicates the viability of the system to 

meet the proposed intended function, specifically including the calculated performance of the 

sensor operation within the range of the environment proposed.

3. Likewise, since the purpose of the EFVS sensor is to provide a visual 

advantage over the pilot’s out-the-window view, the general performance analysis should include 

the calculated transmission of electromagnetic energy in the visible spectrum and other 

frequencies that can assess length of transmission over a path with generalized extinction 

coefficients at a given wavelength.

Note: Examples of acceptable sensor models are MODTRAN and LOWTRAN 

which can be used to estimate the performance of infrared systems. Other models (FASCODE) 

for radar systems may be used for these types of sensors and provide a basic measure of signal 
MM/DD/YYYY AC 20-167A

27

attenuation helpful in assessing performance and viability for the functions defined in 14 CFR 

91.176.

4. Minimum system performance. Integration of the major components 

includes the installed sensor, its interconnections with the sensor display processor, the display

device, pilot interface, and aircraft mechanical interface, which can include the radome for the 

sensor.

(a) Latency. EFVS latency should be no greater than 100 milliseconds 

(msec). A longer lag time can be found satisfactory, provided it is demonstrated not to be 

misleading or confusing to the pilot. Latency, as a general requirement, should not be 

discernible to the pilot and should not affect control performance or increase pilot workload. 

EFVS latency causes, at best, undesirable oscillatory image motion in response to pilot control 

inputs or turbulence. At worst, EFVS latency may cause pilot-induced oscillations if the pilot 

attempts to use the EFVS for active control during precision tracking tasks or maneuvers in the 

absence of other visual cues.

(b) EFVS FOR. The minimum fixed FOR should be 20 degrees 

horizontal and 15 degrees vertical. In applications where the FOR is centered on the flight path 

vector the minimum vertical FOR should be 5 degrees (± 2.5 degrees) and 20 degrees horizontal.

(i) The requirement for a minimum EFVS FOR should not 

only consider the HUD FOV (i.e., how large of an area displayed), but also the area over which 

this area subtends (i.e., what is shown on the conformal display). The FOR portrayed on the 

HUD is established by three primary determinants:

(1) HUD and EFVS sensor Field-Of-View;

(2) Orientation of the HUD with respect to the aircraft 

frame of reference (for example, boresight and proximity to pilot’s eye); and

(3) Orientation (for example, attitude) of the aircraft.

(ii) SAE ARP 5288 states, “The design of the HUD installation 

should provide adequate display fields-of-view in order for the HUD to function correctly in all 

anticipated flight attitudes, aircraft configurations, or environmental conditions such as 

crosswinds for which it is approved. Limitations should be clearly specified in the AFM if the 

HUD cannot be used throughout the full aircraft flight envelope.” A quantitative EFVS FOR 

requirement was established as minimum design criteria to be qualitatively checked during 

certification flight test for sufficiency in meeting its intended function. The EFVS FOR 

requirement resulted after consideration of the minimum field of regard criteria for various 

aircraft attitudes and wind conditions using a critical altitude of 200 ft height above touchdown 

zone elevation for EFVS visibility.

(iii) A variable FOR is permissible assuming a slewable sensor 

(i.e., variable field-of-regard), centered on the Flight Path Vector, with a minimum +/- 2.5 deg 

about the flight path vector to allow for momentary flight path perturbations and to allow 

sufficient fore/aft view of the required visual references.

(c) Off-axis rejection. A source in object space greater than 1 degree 

outside the FOV should not result in any perceptible point or edge like image within the field of 
MM/DD/YYYY AC 20-167A

28

view. The EFVS should preclude off-axis information from folding into the primary FOR 

imagery, creating the potential for misleading or distracting imagery.

(d) Jitter. When viewed from the HUD eye reference point, the 

displayed EFVS image jitter amplitude should be less than 0.6 mrad. Jitter for this use is defined 

in SAE ARP 5288. This implies the EFVS and HUD cannot exhibit jitter greater than that of the 

HUD itself.

(e) Flicker. Flicker is brightness variations at frequency above 0.25 

Hz per SAE ARP 5288. The minimum standard for flicker should meet the criteria of 

SAE ARP 5288. Flicker can cause mild fatigue and reduced crew efficiency. This requirement 

implies the EFVS and HUD cannot exhibit flicker greater than that of the HUD itself.

(f) Image artifacts. The EFVS must not exhibit any objectionable 

noise, local disturbances or an artifact that hazardously detracts from the use of the system. The 

EFVS design must minimize display characteristics or artifacts (for example, internal system 

noise, “burlap” overlay, or running water droplets) which obscure the desired image of the scene, 

impair the pilot's ability to detect and identify visual references, mask flight hazards, distract the 

pilot, or otherwise degrade task performance or safety.

(g) Image conformality. The accuracy of the integrated EFVS and 

HUD image should not result in a greater than 5 mrad display error at the center of the display at 

a range of 2000 ft (100 ft altitude on a 3 degree glideslope). In accordance with SAE ARP 5288, 

the total HUD system display accuracy error as measured from the HUD eye reference point, 

should be less than 5.0 mrad at the HUD boresight, with increasing error allowable toward the 

outer edges of the HUD. Errors away from the boresight should be as defined in SAE ARP 

5288. The primary EFVS error components include the installation misalignment of the EFVS 

sensor from aircraft/HUD boresight and sensor parallax. A range parameter is used in the EFVS 

conformability requirement to account for the error component associated with parallax. There 

is no error allowed for the EFVS sensor, since it is assumed any error can be electronically 

compensated during installation. With EFVS operations, the aircraft is flown essentially

irrespective of the EFVS/HUD dynamic error, to the MDA or DA. From this point to 100 ft 

height above touchdown zone elevation, the EFVS conformality error introduces error in the 

pilot’s ability to track along the extended centerline/vertical glide path as the pilot flies the flight 

path vector and glidepath reference line toward the EFVS image of the runway.

(h) Sensor/sensor processor.

(i) Dynamic range. The minimum required dynamic range for 

passive EFVS should be 48 db. For active EFVS, side lobes should be 23 db below the main 

beam, and 40 db dynamic range plus sensitivity time control (STC).

(ii) Sensor image calibration. Visible image calibrations and 

other built-in tests that cannot be achieved within a total latency of 100 milliseconds should

occur only on either pilot command or be coordinated by aircraft data to only occur in noncritical phases of flight. If other than normal imagery is displayed during the non-uniformity

correction (NUC) or other built-in tests, the image must be removed from the pilot’s display. 

This requirement prohibits excessive times to complete maintenance or calibration functions 

which would remove or degrade the EFVS imagery during critical phases of flight, unless the 

pilot commands the action (with full knowledge of effect based on training and experience). 
MM/DD/YYYY AC 20-167A

29

Abnormal imagery should be removed from the display to eliminate the potential for any

misleading information.

(iii) Sensor resolution. As a minimum, the sensor resolution 

performance requirement shall adequately resolve (for pilot identification) the runway threshold 

and the touchdown zone to enable the intended function. For example, a radar-based EFVS 

should resolve a 60 ft wide runway from 200 ft height above touchdown zone elevation with a 

typical 3-degree glide slope. The required sensor resolution was established by providing this 

resolution at a minimum range, allowing the pilot to continue the descent below DA or MDA. 

(These values do not take into account pilot decision time or actual atmospheric conditions, or 

the use of non-precision approaches which may require greater distances.) A 60 ft wide runway

was chosen as the ICAO minimum runway width to support an instrument approach procedure.

(iv) Passive sensor optical distortion. Optical distortion should

be 5 percent or less across the minimal FOR as defined in paragraph 4-5.c.(4)(b) and no greater 

than 8 percent outside the minimal FOR.

(v) Sensor sensitivity. In this context, the EFVS sensor 

sensitivity should be at least a noise equivalent temperature difference (NETD) of 50o mK tested 

at an appropriate ambient temperature, for passive EFVS systems or -20dB sm/sm (square 

meter/square meter) surface at Rmax from 200 ft height above touchdown zone elevation with a 

typical 3-degree glide slope for active EFVS systems. Passive sensors for different visible or 

short-wave infrared sources can require very sensitive detectors, as specified by low noise 

equivalent powers.

(vi) Failure messages. EFVS malfunctions detected by the 

system, and which can adversely affect the normal operation of the EFVS, should be 

annunciated. As a minimum, specific in-flight failure message(s) for sensor failure and frozen 

image must be displayed to the flight crew.

(vii) Blooming. The sensor should incorporate features to 

minimize blooming, which can create an unusable or objectionable image. Objectionable 

blooming is defined as the condition that obscures the required visual cues defined in Figure 3. 

Blooming to the extent the required visual references are no longer distinctly visible and 

identifiable is unacceptable.

(viii) Image persistence. The image persistence time constant 

should be less than 100 milliseconds. However, burn-in or longer image persistence caused by 

high energy sources (for example, the sun saturating the infrared sensor elements), should be 

removed from the image to comply with paragraph 4-5, c.(4)(f), Image artifacts, by a secondary

on-demand process (for example, the NUC process).

(ix) Dead pixels. Dead pixels or sensor elements replaced by a 

“bad pixel” replacement algorithm should be limited to 1 percent average of the total display

area, with no cluster greater than 0.02 percent within the minimum FOR. A small number of 

disparate dead pixel elements can be effectively replaced by image processing but eventually, the 

algorithms will degrade the image quality and accuracy due to the sheer number and closelyspaced location of the element.

(x) Parallax. The effects of parallax caused by lateral, vertical, 

and longitudinal offset of the sensor from the pilots’ design eye points cannot impede the EFVS 
MM/DD/YYYY AC 20-167A

30

from performing its intended function, as evaluated during flight test. Parallax should not result 

in significant performance differences in safety-related performance parameters (e.g., flare 

height; sink rate, touchdown location; groundspeed during landing, exit and taxi) between EFVS 

operations and visual operations in the same aircraft.
MM/DD/YYYY AC 20-167A

31

Chapter 5. Systems Installation Considerations

5-1. EVS/SVS/CVS Installations Considerations

a. EVS/SVS/CVS Pilot Controls.

1. The EVS/SVS/CVS display controls should be visible to, and within reach 

of, the pilot flying from any normal seated position. The position and movement of the controls 

should not lead to inadvertent operation.

2. The EVS/SVS/CVS controls, except those located on the pilot’s control 

wheel, must be adequately illuminated for all normal background lighting conditions and must 

not create any objectionable reflections on other flight instruments.

3. There must be a means to modulate illumination unless fixed illumination 

of the EVS/SVS/CVS controls is shown to be satisfactory under all lighting conditions.

b. EVS/SVS/CVS Preventive Maintenance. Use manufacturer data for preventive 

maintenance (for example, Instructions for Continued Airworthiness, per 14 CFR 21.50 and 

FAA Order 8110.54), or other methods, techniques, and practices acceptable to the 

Administrator.

c. EVS/SVS/CVS Built-In Test (BIT). Provide a BIT capability that, at a minimum, 

limits the exposure time to latent failures consistent with the exposure limits in the system safety 

assessment.

d. The electrical system must be able to furnish the required power at the proper 

voltage for the EVS/SVS/CVS.

e. EVS/SVS/CVS System Safety Design Criteria. The overall safety requirement of 

the aircraft is based on installed equipment. A complete fault hazard analysis (FHA) and system 

safety analysis (SSA) should be conducted to identify failure modes and classify the hazard 

levels. To meet the safety criteria, the system design will be demonstrated through analysis and 

engineering tests to preclude failures that can cause hazardously misleading information to be 

presented to the pilot or crew, or which can otherwise subsequently cause an unsafe condition. 

The following guidelines do not preclude the results of a full SSA. The results of an SSA found 

acceptable to the FAA should prevail.

f. EVS/SVS/CVS Required Safety Level.

1. The airworthiness standard under which approval is sought can impact 

criticality (for example, 14 CFR part 23, 25, 27, or 29). Recognizing that each implementation 

and integration of each installation can be unique, the applicant should perform a thorough FHA, 

SSA, and Failure Mode and Effects Analysis (FMEA). Any failure or malfunction that could 

cause misleading enhanced vision, synthetic vision, or combined vision depiction should be 

immediately annunciated and the imagery depiction should be removed.

2. The applicant must perform a safety assessment as required by the 

regulations, based on the proposed installation for the given aircraft and intended function for 

each phase of flight. Information presented to a pilot on a PFD is considered truth unless flagged 

otherwise. Therefore, presenting hazardously misleading information to the pilot must be 

avoided. One example of hazardously misleading information (HMI) would be the aircraft level 
MM/DD/YYYY AC 20-167A

32

ramifications of a “frozen EVS/SVS/CVS display” that is undetected by the flight crew. In 

general, the sensor or system performance and level of design must be consistent with the safety

assessment.

3. Once the safety assessment has been completed, for any hazard or failure 

classification greater than Major, a fault tree analysis (FTA) should be evaluated using the 

guidance found in the FAA system safety advisory circular that is applicable to the installation 

(e.g., AC 23.1309-1E, AC 25.1309-1A, AC 27-1B (containing AC 27.1309) and 29-2C). The 

FTA should include the display monitor, power supply, IR camera and sensors, cable, status 

annunciations, and other components that affect the top-level events. The FTA should not 

include pilot detection and corrective actions, which have no fixed probability value.

4. The variables influencing the outcome of the failure condition and its 

classification vary between 14 CFR parts 23, 25, 27, and 29. In general, the sensor or system 

performance and level of design shall be consistent with the SSA. Table 2 provides sample 

system operating phases for consideration. The results of an SSA found acceptable to the FAA 

should prevail.

Table 2. System Operating Phases for Considerations

GROUND TAKEOFF IN-FLIGHT LANDING

(1)Taxi

(2) Maintenance

(1) Takeoff Roll Prior 

to V1,

(2) Takeoff Roll After 

V1,

(3) Takeoff After VR

to 200’

(4) Rejected Takeoff

(1) Climb

(2) Gear Up,

(3) Cruise

(4) Descent,

(5) Gear Down,

(6) Approach 200’ to 

0’

(7) Go Around

(1) Touchdown & 

Rollout

(2) Taxi

5. The normal operation of the EVS/SVS/CVS may not adversely affect, or 

be adversely affected by other normally operating aircraft systems. The criticality of the 

EVS/SVS/CVS system’s function to display imagery, including the potential to display

hazardously misleading information, should be assessed according to the applicable 14 CFR part 

2x.1309, AC 25-11A chapter 4, and AC 2x.1309, System Safety Analysis and Assessment for 

Part 23/25 Airplanes. Likewise, the hazard effects of any malfunction of the EVS/SVS/ CVS 

that could adversely affect interfaced equipment or associated systems should be determined and 

assessed according to the applicable 14 CFR 2x.1309, AC 25-11A chapter 4, and AC 2x.1309. 

As applicable, similar criteria is found in SAE ARP 4754, and ARP 4761.

g. EVS/SVS/CVS Environmental Specifications. The EVS/SVS/CVS should meet 

all specified operating conditions and should provide required operating performance, life and 

reliability when operating within the aircraft and subsystem flight envelope as specified in 

RTCA/DO-160G (as revised) Environmental Conditions and Test Procedures for Airborne 

Equipment. These criteria must also include the high-intensity radiated fields (HIRF), 
MM/DD/YYYY AC 20-167A

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electromagnetic interference (EMI) and lightning requirements as specified in the certification 

basis of the aircraft to be installed. A lightning zone analysis and assessment of the effects of 

lightning strike on the camera in conjunction with other cockpit equipment should be 

accomplished. The installation must protect the aircraft against catastrophic effects from 

lightning.

5-2. EFVS Installation Considerations

a. EFVS Annunciations. Any modes of EFVS operation should be annunciated on 

the flight deck and visible to the crew. The modes of the EFVS operation must be made 

available to the flight data recorder as required.

b. EFVS Display.

1. Display resolution of the HUD. Since the sensor can be active or passive, 

the EFVS display should adequately resolve a 60 ft. wide runway from 200 ft. height above 

touchdown zone elevation with a typical 3-degree glide slope. The pilot needs to be able to 

detect and accurately identify the visual references in the image.

2. Imagery and symbology display. Imagery must not degrade presentation 

of essential flight information on the HUD. The pilot's ability to see and use the required 

primary flight display information such as primary attitude, airspeed, altitude, and command bars 

must not be hindered or compromised by the EFVS image on the HUD.

3. Flare Cue. An EFVS II must have a flare cue because it is intended to 

enable landing in low visibility. The flare cue, whether a flare prompt or flare guidance, should

demonstrate compliance to the landing criteria found in paragraph 6-2. For some aircraft, flare 

guidance may be required because a flare prompt is not sufficient.

(a) Flare Prompt. A flare prompt is intended to notify the pilot that it is 

time to initiate the flare maneuver, but does not guide the pilot’s manual pitch control inputs. 

The pilot must use situational information (e.g., altitude, vertical rate, attitude, FPV, perspective 

view of the runway) from the EFVS to judge the magnitude and rate of manual pitch control 

inputs. The appearance and dynamic behavior of the flare prompt should be distinguishable 

from command guidance. The flare prompt should appear timely and conspicuously to the pilot 

using the HUD so that the flare maneuver will be neither too early nor and within the touchdown 

zone as described in paragraph 6-2 of this document.

(b) Flare Guidance. EFVS II operations require a flare cue-either flare 

prompt or flare guidance, as appropriate, for achieving acceptable touchdown performance. 

Each applicant for a type design approval must demonstrate acceptable touchdown performance 

for their particular EFVS implementation using either flare prompt or flare guidance. This 

provides the pilot with additional information to conduct the flare maneuver during conditions of 

low visibility typically encountered during EFVS operations to touchdown and rollout. The flare 

cue should be demonstrated to meet the landing criteria found in paragraph 6-2. 

c. EFVS Maintenance. Instructions for Continued Airworthiness are to be furnished 

after final design approval (reference 14 CFR 21.50 and FAA Order 8110.54).

d. EFVS Built-in Test (BIT). Provide a BIT capability (or equivalent means) that, at 

a minimum, limits the exposure time to latent failures in support of the system safety assessment.

e. EFVS System Safety Design Criteria.
MM/DD/YYYY AC 20-167A

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1. The overall level of safety of the aircraft is based on installed equipment. 

A complete system safety analysis (SSA) should be conducted to identify failure modes and 

classify the hazard levels. To meet the safety criteria, the system design should preclude failures 

that can cause hazardously misleading information (HMI) to be presented to the pilot or crew, or 

which can otherwise subsequently cause an unsafe condition. For example, HMI could include 

information providing attitude, altitude, and distance cues as outside terrain imagery. This 

demonstration should be accomplished through analysis and engineering tests. 

(a) The EFVS system must perform its intended function for each 

operation and phase of flight that it would use.

(b) The normal operation of the EFVS cannot adversely affect, or be 

adversely affected by other aircraft systems. Annunciate detected malfunctions of the EFVS 

system and remove the malfunctioning display elements.

2. Appendix 2, Table 4 lists the categories of systems and failure 

probabilities to meet the safety criteria in 14 CFR part 25 airplanes (AC 25.1309-1A). For 14 

CFR part 23 aircraft, similar information can be found in 14 CFR 23.1309 and AC 23.1309. The 

relationship among airplane classes, probabilities, severity of failure conditions and software 

development assurance levels is found in AC 23.1309-1E. Section 2x.1309, as applicable, and 

the following additional guidance helps assess the criticality of the EFVS display, including the 

potential to display HMI:

(a) AC 25-11A (chapter 4),

(b) AC 23.1311-1, and

(c) AC 27-1B and AC 29-2C, as appropriate for the installation.

3. Validate all alleviating flightcrew actions that are considered in the EFVS 

safety analysis during testing either for incorporation in the AFM/AFMS or RFM/RFMS 

limitation section, procedures section or for inclusion in type-specific training.

f. EFVS I Required Level of Safety.

1. When you are designing an EFVS I, establish safety design goals for 

airworthiness approval. The safety criteria for each phase of flight, including approach and 

landing systems are defined in terms of accuracy, continuity, availability, and integrity. FAA 

design guidance provides criteria to determine the overall required level of safety for the aircraft, 

in any mode of flight, for any combination of failures which can cause an unsafe condition to be 

fully assessed and categorized. This includes the probability of the pilot(s) to cope with these 

failures. The hazard level for any aircraft system depends on the ability of the pilot(s) to cope 

with failures. For failures where the SSA assumes a particular pilot intervention to limit the 

hazard effects, for example from Catastrophic or Hazardous to Major or Minor, the applicant 

must show that pilot indeed can be relied on to perform that intervention. For example, the pilot 

might be assumed to detect a system error because of other displays or view out the window. It 

must be demonstrated that pilots will indeed detect the error in a timely fashion and not be 

hazardously misled. The demonstration must validate the proposed hazard classification, as 

applicable (see Appendix 2, Table 4).
MM/DD/YYYY AC 20-167A

35

2. The applicant should demonstrate a satisfactory safety (failure and 

performance) level which must not be less than the safety level required for non-EFVS I based 

precision and non-precision approaches with decision altitudes of 200 ft. or above. In showing 

compliance, probabilities cannot be factored by the portion of approaches which are made using 

EFVS. Consideration, however, can be given to the EFVS I critical flight time, such as from the 

highest DH that can be expected for an EFVS I based approach to 100 ft. above the TDZE.

3. The design assurance levels (DALs) are directly linked to the specific 

intended use and to the specific EFVS I installation as an integrated part of the cockpit flight 

information system.

4. There are failure modes within the EFVS I which determine that software 

and hardware DALs should be RTCA/DO-178B or level C (major) as a minimum. However, 

dependent upon the mitigations you utilize, stemming from the specific EFVS and cockpit 

installations, the DALs can be higher than this minimum level.

5. The aircraft level functional hazard analysis (FHA) you prepare should

determine whether the minimum required DALs of level C are adequate for your specific 

installation. An example FHA is shown in Appendix 2, but is a model case only and cannot be 

applied to any specific aircraft without independent analysis.

6. A system safety analysis (SSA) of an EFVS I was performed for a 

certification on an instrument flight capable aircraft for straight-in non-precision and precision 

approach and landing operation per 14 CFR 91.176(b). This SSA is shown in appendix 2 for 

example and general guidance only. The applicant must provide the applicable 14 CFR 23, 25, 

27, and 29.1309 analysis.

7. Conduct a safety analysis to show the EFVS I system meets all the 

integrity criteria for the aircraft, HUD and EFVS. Demonstrate system and subsystem 

malfunctions which are not shown to be extremely improbable as appropriate in a simulation or 

in flight. The malfunction annunciation and fault detection schemes must achieve the 

determined level of safety.

g. EFVS II Required Level of Safety.

1. The applicant is must demonstrate a satisfactory level of safety (failure 

and performance) appropriate to the operations being addressed, but with the visual segment 

primarily accomplished by the use of an EFVS II rather than natural vision.

2. To achieve the required safety level, the minimum baseline safety levels 

required for the installed EFVS II equipment regardless of visibility, should be dependent on the 

demonstrated performance.

3. An aircraft level Functional Hazard Analysis (FHA) and System Safety 

Assessment (SSA) should be prepared by the applicant to assess the hazard level associated with 

system failure conditions and to determine the minimum required software and hardware Design 

Assurance Levels (DAL) based on the applicant’s specific installation. Mitigating system design 

features include redundancy, independent guidance display, system monitoring, pilot in the loop, 

pilot not flying, etc. In no case should the DAL be less than DAL C.

4. The minimum required safety level for an EFVS II system (EFVS to 

touchdown in visibilities not less than RVR 1000 feet) is based on the assumption the minimum 
MM/DD/YYYY AC 20-167A

36

visibility limitation of 1000 feet provides the flight crew a means to verify that the aircraft is 

safely approaching the runway for EFVS II-based landing, or, if not, to initiate a timely go 

around. This provides additional integrity to the operation. Depending on the applicant’s 

design, it may be possible that the minimum visibility can also compensate for loss of EFVS 

imagery, such that the pilot can use the remaining symbolic flight information on the HUD and 

the external view to safely land. System evaluation should consider EFVS II failure modes and 

whether the pilot can safely land and rollout with available natural vision plus whatever remains 

of EFVS II. A Safe landing should not be assumed with only available natural vision after total 

loss of EFVS II (i.e., symbology and image).

5. In showing compliance with these safety criteria, do not factor 

probabilities of EFVS II failure conditions by the fraction of approaches which require EFVS II. 

Also, do not factor probabilities of EFVS II failure conditions by a statistical distribution of 

visibility conditions. The exposure time used for EFVS II failure calculations should be the 

elapsed time from descent below the highest expected DA/DH for the EFVS II based approach to 

completion of rollout to a safe taxi speed.

h. System Safety Assessment.

1. An aircraft level Functional Hazard Analysis (FHA) should be prepared by 

the applicant to assess the hazard level associated with system failure conditions and to 

determine that the minimum required software and hardware Design Assurance Level (DALs) is 

appropriate to the applicant’s specific intended function.

2. The DALs are directly linked to the specific intended use and to the 

specific EFVS installation as an integrated part of the cockpit flight information system. The 

availability and integrity of situational and flight path information from sources other than the 

EFVS image and the ability of the pilot monitoring to monitor the operation should be 

considered when assessing the appropriate hazard levels for the EFVS.

3. The applicant should provide a System Safety Assessment (SSA) for 

compliance to the applicable to 14 CFR 2X.1309 regulation.

4. The safety assessment should show that the applicant’s specific 

installation meets all the integrity criteria for the aircraft systems, HUD and EFVS.

5. The applicant may need to demonstrate by flight test or simulation, 

combinations of EFVS malfunctions which are not shown to be extremely improbable (10 E-9) 

be demonstrated.

6. Any malfunction fault detection and annunciation schemes must satisfy

the required levels of safety and must perform their intended functions.

7. All aircraft configurations to be certified must be addressed.

i. EFVS Fail Safe Features. The normal operation of the EFVS may not adversely

affect, or be adversely affected by other normally operating aircraft systems. Malfunctions of the 

EFVS which could cause display of misleading information must be annunciated and the 

misleading information removed. The criticality of the EFVS’s function to display imagery, 

including the potential to display hazardously misleading information, should be assessed 

according to 14 CFR 25.1309, AC 25-11A chapter 4, and AC 25.1309-1A. Likewise, the hazard 

effects of any malfunction of the EFVS that could adversely affect interfaced equipment or 
MM/DD/YYYY AC 20-167A

37

associated systems should be determined and assessed according to 14 CFR 25.1309, AC 25-

11A chapter 4, and AC 25.1309-1A. As applicable, similar criteria is found in 14 CFR 23.1309, 

and AC 23.1309-1C, 14 CFR 27.1309 and AC 27-1B and 14 CFR 29.1309 and AC 29-2C. This 

requirement must be met through a system safety assessment and documented via FTA, failure 

mode and effects analysis (FMEA), and failure mode and effects analysis substantiation (FMEA 

Substantiation), or equivalent safety documentation.

j. EFVS Environmental Specifications. The EFVS must meet all specified 

operating criteria and must provide required operating performance, life and reliability when 

operating within the aircraft and subsystem flight envelope as specified in RTCA/DO-160F (as 

revised) Environmental Conditions and Test Procedures for Airborne Equipment, or future 

versions. These criteria must also include the HIRF, EMI and lightning requirements as 

specified in the certification basis of the aircraft to be installed.

5-3. HIRF Considerations for All Installations (EVS, SVS, CVS, and EFVS).

a. The immunity of critical avionics/electronics and electrical systems to HighIntensity Radiated Fields (HIRF) must be established. Critical functions are those whose failure 

would contribute to or cause a failure condition that would prevent the continued safe flight and 

landing of the aircraft. Refer to AC 20-158, The Certification of Aircraft Electrical and 

Electronic Systems for Operation in the High-Intensity Radiated Fields (HIRF) Environment, for 

compatibility with other systems.

b. New avionics/electronics and electrical systems performing critical functions 

should be designed and installed to preclude component damage and interruption of function due 

to both the direct and indirect effects of HIRF. For these systems, compliance must be shown to 

14 CFR 23.1308(a), 25.13l7(a), 27.13l7(a), or 29.1317(a), as appropriate.

Note: AC 20-158 (paragraph 6) provides guidance on Approaches to Compliance.
MM/DD/YYYY AC 20-167A

38

Chapter 6. Performance Evaluation

6-1. EVS/SVS/EFVS Performance Demonstration

a. The performance demonstration, establishing aircraft system compliance with 

applicable FAA regulations, typically includes bench testing, flight testing, data collection, and 

data reduction to show that the proposed performance criteria can be met. Minimal performance 

standards necessitate an evaluation of the system used during anticipated operational scenarios. 

The performance evaluations should therefore include demonstrations of taxi, take-off, approach, 

missed approaches, failure conditions, cross wind conditions, and approaches into specific 

airports as appropriate for the system’s intended function. For EFVS, the applicant should

demonstrate performance at the lateral and vertical limits for the type of approach (for example, 

precision, non-precision, and approach with vertical guidance) credit being sought. Appendix 4 

provides sample EFVS flight test considerations.

b. No specific test procedures are cited, as it is recognized that alternative methods 

can be used. Alternate procedures can be used if it can be demonstrated that they provide all the 

information needed to show compliance with the applicable regulations. System performance 

tests as they relate to operational capability are the most important tests. Subsystem tests are 

used as subsystems are added during system buildup to ensure appropriate subsystem 

performance as it relates to overall system performance.

c. The applicant should use any of these four general verification methods (refer to 

AC 25.1329-1B, AC 23.1309, AC 27-1B or AC29-2C as applicable)..

1. Analysis. Demonstrate compliance using an engineering analysis.

2. Flight Test. Demonstrate compliance using an appropriate aircraft (in the 

air or on the ground).

3. Laboratory Test. Demonstrate compliance using an engineering bench 

representative of the final EVS/SVS/CVS/EFVS system being certified.

4. Simulation. Demonstrate compliance using a flight simulator.

d. Specify the individual verification methods that you use in the certification plan. 

Confirm the appropriate certification office agrees with your plan before you begin. For 

extensions, features, and design decisions not explicitly specified in this AC, conduct human 

factors evaluations. Conduct these evaluations through bench, simulation, or flight testing.

e. Verify both the installed system and the individual system components meet the 

EVS/SVS/CVS/EFVS criteria described in Chapter 4.

f. Demonstrate the system meets performance criteria by flight test and other 

appropriate means, which can include use of a flight simulator. An example of a flight test 

program for EFVS is described in appendix 4 in this AC. The flight test program assumes that 

the guidance system utilized to satisfactorily position the aircraft at the DA/DH or MDA has 

been separately tested and shown to fully perform its intended function. Testing and data 

collection to demonstrate this is not part of this document.

g. Airframe and equipment manufacturer based tests or analysis, as applicable,

should be developed and conducted to validate the detailed system criteria. No specific test 
MM/DD/YYYY AC 20-167A

39

procedures are cited because alternative methods can be used. You can use alternate procedures 

if you can demonstrate that they provide all the required information. System performance tests 

as they relate to operational capability are the most important tests. Subsystem tests are used as 

subsystems are added during system buildup to ensure appropriate subsystem performance as it 

relates to overall system performance.

h. Conduct an evaluation of the system used during anticipated operational 

scenarios.

i. For EFVS testing: If the aircraft has all elements of 14 CFR 91.176(a)(1) and 

91.176(b)(1), as appropriate for EFVS operations to touchdown and roll-out or EFVS operations 

to 100 feet, and as documented in the Type Inspection Acceptance, it can proceed with the 

number of approaches per the approved test plan. Use of a build-up approach should facilitate 

the process obtaining a waiver to conduct flight test of an uncertified system. 

6-2. Performance Demonstration of EFVS II.

a. Where appropriate for the performance demonstration, the non-visual conditions 

can be achieved either by natural obscuration or by use of a visibility limiting device in front of 

the pilot. Caution should be used if the applicant chooses to use a visibility limiting device for 

system performance demonstrations. Visibility-limiting devices may not adequately simulate 

low visibility conditions for all EFVS II landing performance demonstrations because of the 

unrealistically good external visibility outside the HUD FOV and the unrealistic EFVS II image 

performance in good atmospheric conditions.

b. The workload associated with the use of EFVS II for approach, landing and 

rollout must be considered when showing compliance with 14 CFR 23/25/27/29.1523.

c. Final approach course offsets greater than 3 degrees will be subject to additional 

flight test evaluation. The maximum allowable final approach course offset is established by

flight test. These tests should include the factors related to the offset, such as HUD/EFVS field 

of view, crosswinds, and the maximum drift angle for a conformal flight path vector.

d. The EFVS II image, with superimposed flight symbology, must not mislead, 

distract or jeopardize the safety of the landing and rollout. Performance shall be demonstrated to 

be equivalent or better to that normally achieved in visual operations for the specific aircraft for 

all performance parameters measured.

e. Benchmark data establishing equivalence to normal visual operations with the 

specific aircraft would not normally be necessary. However, if flight test results show deviations 

for the standard criteria listed above, then benchmark data might be used to establish the 

equivalence of EFVS II operations to normal visual operations for that specific aircraft.

f. Without requiring exceptional pilot skill, alerting, strength or workload, the 

image/symbology should provide the visual cues for the pilot to perform the following items.

1. Speed control within +10/-5 knots of the approach speed, whether 

manually controlled or with auto-throttle, as proposed by the applicant, up to the point where the 

throttles are retarded for landing.

2. A smooth transition through flare to landing.

3. Approach, flare, and landing at a normal sink rate for the aircraft.
MM/DD/YYYY AC 20-167A

40

4. All touchdowns in the touchdown zone. Lateral touchdown performance 

must be demonstrated to be equivalent or better than that achieved in visual operations for the 

specific aircraft. Longitudinal touchdown performance must be demonstrated within the first 

third, or the first 3000ft, of the runway, whichever is more restrictive, and demonstrated to be 

equivalent or better than that achieved in visual operations for the specific aircraft.

5. Prompt and predictable correction of any lateral deviation away from the 

runway centerline to smoothly intercept the centerline.

6. Touchdowns with a bank angle that is not hazardous to the airplane.

7. Demonstrated performance of the installed EFVS at representative 

visibilities for EFVS I and EFVS II operations a described in this document, will determine any 

additional limitation (for example, crosswind and offset). 

8. A normal derotation.

9. Satisfactory and smooth control of the path of the airplane along the 

runway centerline through rollout to a safe taxi speed.

10. A safe go around anytime including up to touchdown in all configurations 

to be certified.

6-3. Environmental Qualification.

a. Installed equipment meets the criteria in RTCA/DO-160F (as revised), 

Environmental Conditions and Test Procedures for Airborne Equipment.

b. Design Assurance.

1. Follow the criteria of RTCA/DO-178B or higher, Software Considerations 

in Airborne Systems and Equipment Certification, to conduct software design assurance tests. 

The version must be current at time of application.

2. Follow the criteria of RTCA/DO-254, Design Assurance Guideline for 

Airborne Electronic Hardware, to conduct hardware design assurance tests, if applicable. The 

version must be current at time of application.
MM/DD/YYYY AC 20-167A

A1-1

Appendix 1. FAA EFVS 14 CFR Compliance (Partial List)

1-1. Airworthiness Standards.

a. Certification Procedures for Products and Parts (14 CFR part 21).

b. Normal, Utility, Acrobatic, and Commuter Category Airplanes (14 CFR part 23).

c. Transport Category Airplanes (14 CFR part 25).

d. Normal Category Rotorcraft (14 CFR part 27).

e. Transport Category Rotorcraft (14 CFR part 29).

1-2. EFVS Compliance.

The following requirements address EFVS and are in addition to HUD criteria. The amount of 

new test data can be determined by the individual application, availability, and relevance of data.

Table 3. EFVS Acceptable Methods of Compliance

14 CFR § Description Acceptable Method of 

Compliance

23/25/27/29.251 Vibration and buffeting Flight Test

23/25/27/29.301 Loads Analysis 

23/25/27/29.303 Factor of safety Analysis

23/25/27/29.307 Proof of structure Analysis

25.561/25.562(c)(5)) Emergency landing conditions; 

Head Injury Criterion (HIC)

Analysis

25/27/29.571 and 

23.573 

Damage-tolerance and fatigue 

evaluation of structure

Analysis

25.571(e) Damage-tolerance and fatigue 

evaluation of structure(discrete 

source) evaluation

Analysis and/or Test (See Note)

25.581 Lightning protection Analysis

23/25/27/29.601 General Drawing 
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A1-2

14 CFR § Description Acceptable Method of 

Compliance

23/25/27/29.603 Materials Drawing 

23/25/27/29.605 Fabrication methods Drawing 

23/25/27/29.609 Protection of structure Drawing 

23/25/27/29.611 Accessibility provisions Drawing 

23/25/27/29.613 Material Strength properties and 

material design values

Drawing, Analysis, Test (See 

Note)

23/25/27/29.619 Special factors Analysis

23/25/27/29.625 Fitting Factors Analysis

25.629 (d)(8) Aeroelastic stability Analysis, Test

25.631 Bird strike damage

Analysis, or Test if necessary. 

(Testing should be accomplished 

unless the analysis shows that the 

integrity of the original structure 

has not been compromised by

EFVS installation modification.)

23/25/27/29.771 Pilot compartment Flight Test

23/25/27/29.773 Pilot compartment view Flight Test

23/25/27/29.777 Flight deck controls Flight Test

23/25/27/29.1301 Function and installation Ground Test and Flight Test

23/25/27/29.1309 Equip, systems, and install Analysis and/or Test and Design 

data

25.1316 System lightning protection Analysis and Ground Test
MM/DD/YYYY AC 20-167A

A1-3

14 CFR § Description Acceptable Method of 

Compliance

23.1308, and 

25/27/29.1317

High-intensity Radiated Fields

(HIRF) Protection

Ground Test and Flight Test 

Analysis/Data

23/25/27/29.1321 Arrangement and visibility Ground Test and Flight Test

23/25/27/29.1322 Warning, caution, advisory lights Ground Test and Flight Test

25.1323 Airspeed indicating systems Flight Test

25.1335 Flight director systems Ground Test and Flight Test

23/27.1351 Electrical Systems and 

Equipment; General

Analysis

25/29.1353 Electrical equipment and 

installation Analysis

23/25/27/29.1357 Circuit protective devices Analysis and Ground Test

23/25/27/29.1381 Instrument lights Ground Test and Flight Test

23/25/27/29.1419 Ice protection Analysis

23/25/29.1431(a)(c) Electronic equipment Analysis and Ground Test

23/25/27/29.1459(e) Flight data recorders Flight test

23/25/27/29.1501 Operating Limitations and 

Information; General

Flight Test

23/25/27/29.1523 Minimum flight crew Flight Test or Simulation

23/25/27/29.1525 Kinds of operation Flight Test

23/25/27/29.1529 Instructions for Continued 

Airworthiness

Design Data
MM/DD/YYYY AC 20-167A

A1-4

14 CFR § Description Acceptable Method of 

Compliance

23/25/27/29.1581 Aircraft flight manual; General Design Data and Flight Test

23/25/27/29.1583 Operating limitations Flight Test Data

23/25/27/29.1585 Operating procedures Flight Test Data

26.47 Holders of and applicants for a 

supplemental type certificate -

alterations and repairs to 

alterations.

Analysis

.

Note: In some cases, previously approved test data for the aircraft may be resubmitted 

for compliance, if analysis can establish that the test data remains valid for the aircraft with the 

new modification.
MM/DD/YYYY AC 20-167A

A2-1

Appendix 2. EFVS I and EFVS II Systems Safety Guidance

2-1. General.

a. Safety Criteria. Safety criteria for approach and landing systems generally 

consider four elements: accuracy, continuity, availability, and integrity. These criteria apply to 

both the external navigation systems as well as airborne navigation equipment. Trajectory

management or flight technical error, which can be interpreted as signal structure contributing to 

roughness, bends and scalloping of ILS-based guidance, should also be considered. They also 

define how the airspace and aircraft are integrated together to make a safe approach and landing. 

The FAA developed, in conjunction with the other governments, definitions related to safety and 

performance for a landing system.

b. Transport Category Airplanes. For aircraft systems, 14 CFR 25.1309 defines the 

safety requirement and AC 25.1309 defines the means for verification. The probability of each 

catastrophic failure condition must be 10 -9or less per flight hour considering any mode of flight, 

any combination of failures causing an unsafe condition, and including the probability of the 

crew to cope with the failures. The FAA accepts this number to assure a negligible adverse 

effect on accident rates, and to help reduce them as new systems come on line.

c. General Aviation or Non-Transport Category Airplanes. Similar information can 

be found in 14 CFR 23.1309 and AC 23.1309. The relationship among airplane classes, 

probabilities, severity of failure conditions and software development assurance levels is found 

in AC 23.1309-1.

d. Rotorcraft. Similar information can be found in 14 CFR 27.1309 and AC 27-1B 

and 14 CFR 29.1039 and AC 29-2C.

2-2. Required Level of Safety.

The required level of safety for any aircraft systems, therefore, depends on the ability of the crew 

to cope with failures as shown in Table 3, which lists the categories of systems and failure 

probabilities to meet the safety criteria in 14 CFR parts 23 and 25 airplanes. For part 23 

airplanes, similar information can be found in 14 CFR 23.1309 and AC 23.1309-1D. The 

relationship among airplane classes, probabilities, severity of failure conditions and software 

development assurance levels is found in AC 23.1309-1E.

Table 4. Required Level of Safety, 14 CFR part 25 Aircraft

Required Level of Safety, 14 CFR part 25 airplanes

Classification Effect Target Probability P 

Minor Slight reduction in safety margins or functional 

capabilities.

Slight increase in crew workload.

Some inconvenience to occupants.

10E-3 > P > 1E-5
MM/DD/YYYY AC 20-167A

A2-2

Major Significant reduction in safety margins or functional 

capabilities.

Significant increase in crew workload or in conditions 

impairing crew efficiency.

Some discomfort to occupants.

10E-5 > P > 1E-7

Hazardous/ 

Severe Major 

Large reduction in safety margins or functional 

capabilities.

Higher workload or physical distress such that the 

crew could not be relied upon to perform tasks 

accurately or completely.

Adverse effects upon occupants including serious or 

fatal injury to a relatively small number of occupants 

other than the flight crew.

10E-7 > P > 1E-9

Catastrophic Failure conditions which would prevent continued 

safe flight and landing, resulting in multiple fatalities, 

usually with the loss of the airplane.

10E-9 > P

2-3. Demonstration.

To meet the safety criteria, the EFVS design will be demonstrated through analysis and 

engineering tests to preclude any critical failure combinations that can cause hazardously 

misleading information to be presented to the crew, or which can otherwise subsequently cause 

an unsafe condition. Failures which are self-evident or made obvious to the crew, and with 

which they can safely cope, need not be specifically monitored.

2-4. State Data.

The aircraft state data is provided by the standard inertial, air data, and radio guidance sensors. 

The HUD or display processor will be required to be at a sufficient level of safety for the aircraft 

type and application to detect critical random or common faults that could otherwise cause an 

unsafe condition. The ability to continue the approach below the standard Category I

DA/DH/MDA/MDH therefore is strictly borne by the pilot, a safety factor already accounted for 

in the safety analysis for standard Category I operations. The example below in Table 5 is a 

model case and cannot be applied for any specific aircraft. Functional hazard assessments as 

required by the FAA are aircraft and systems specific.
MM/DD/YYYY AC 20-167A

A2-3

Table 5. Example EFVS/HUD Functional Hazard Assessment, 14 CFR part 25 Aircraft, 

ILS Approaches to 100 ft Height Above Touchdown, RVR 1200 ft

FHA

NO.

FAILURE 

CONDITION PHASE OF FLIGHT

PILOT 

ACTION

HAZARD 

INDEX OBJECTIVE

1.0 LOSS OF 

FUNCTION

1.1 Loss of EFVS 

imagery on HUD

Taxi and Takeoff 

Enroute 

Terminal Arrival 

Final Approach -

Above 100 ft. EFVS 

height above 

touchdown zone 

elevation 

Go-Around

Crew would 

revert to 

standard headup and/or head 

down 

procedures

MINOR 10E-3

1.2 Loss of EFVS 

imagery on HUD

Final Approach - From 

100 ft. height above 

touchdown zone 

elevation to Landing 

Crew would 

perform a goaround or 

possibly a 

minimum flare 

landing

MINOR 10E-3

1.3 Loss of HUD 

symbology

Taxi and Takeoff 

Enroute

Terminal Arrival 

Final Approach -

Above 100 ft. height 

above touchdown zone 

elevation

Go-Around

Crew would 

revert to 

standard head 

down 

procedures

MINOR 10E-3

1.4 Loss of HUD 

symbology

Final Approach - From 

100 ft. height above 

touchdown zone

elevation to Landing

Pilot would 

continue the 

approach and 

land

MINOR 10E-3

1.5 Loss of HUD and 

EFVS Imagery

Final Approach - From 

100 ft. height above 

touchdown zone 

elevation to Landing

Pilot would 

continue the 

approach and 

land

MINOR 10E-3
MM/DD/YYYY AC 20-167A

A2-4

FHA

NO.

FAILURE 

CONDITION PHASE OF FLIGHT

FAILURE 

EFFECT

HAZARD 

INDEX OBJECTIVE

2.0 MISLEADING 

INFORMATION

2.1 Misleading EFVS 

imagery on HUD

Taxi 

Enroute

Terminal Arrival 

Final Approach -

Above 100 ft height 

above touchdown 

zone elevation

Go-Around

Crew would 

revert to 

standard head 

down 

procedures

MINOR 10E-3

2.2 Misleading EFVS 

imagery on HUD

Final Approach -

From 100 ft. height 

above touchdown 

zone elevation to 

Landing

Crew would 

perform a goaround or 

possibly a 

minimum flare 

landing

MAJOR 10E-5

2.3 Misleading HUD 

symbology

Taxi and Takeoff 

Enroute

Terminal Arrival 

Final Approach -

Above 100 ft. height 

above touchdown 

zone elevation

Final Approach -

From 100 ft. height 

above touchdown 

zone elevation to 

Landing

Go-Around

Pilot would take 

appropriate 

action as 

defined in AFM 

for standard 

displays and 

HUD 

Various 

failure 

conditions 

with the 

highest 

hazard 

index 

being 

MAJOR

Various failure 

conditions with 

the highest 

objective being 

10E-5

2.4 Misleading EFVS 

imagery and 

HUD symbology

Final Approach -

Above 100 ft. height 

above touchdown 

zone elevation

Copilot would

recognize 

condition using 

copilot's PFD

MAJOR 10E-5

2.5 Misleading EFVS 

imagery and 

HUD symbology

Final Approach -

From 100 ft. height 

above touchdown 

zone elevation to 

Landing

Crew would 

perform a goaround or 

possibly a 

minimum flare 

landing

MAJOR 10E-5
MM/DD/YYYY AC 20-167A

A2-5

FHA

NO.

FAILURE 

CONDITION PHASE OF FLIGHT

FAILURE 

EFFECT

HAZARD 

INDEX OBJECTIVE

3.0 OBSTRUCTION 

OF PILOT'S 

VIEW 

3.1 Obstruction of the 

pilot's view 

through the HUD

Takeoff Pilot would 

abort takeoff 

prior to V1

MAJOR 10E-5

3.2 Obstruction of the 

pilot's view 

through the HUD

Taxi 

Enroute

Terminal Arrival

Pilot would take 

appropriate 

action

MINOR 10E-3

3.3 Obstruction of the 

pilot's view 

through the HUD

Final Approach -

Above 100 ft. height 

above touchdown zone 

elevation

Go-Around

Pilot would take 

appropriate 

action

MAJOR 10E-5

3.4 Obstruction of the 

pilot's view 

through the HUD

Final Approach - From 

100 ft. height above 

touchdown zone 

elevation to Landing

Pilot would 

execute a goaround

MAJOR 10E-5
MM/DD/YYYY AC 20-167A

A3-1

Appendix 3. EFVS I and II Safety Standards

3-1. Safety factors for EFVS described in this AC

Safety standards for the following factors include:

a. An acceptable degree of interference of the window or “window and HUD” view, 

potential image misalignment, distortion, and the potential for pilot confusion or misleading 

information.

b. Determination of EFVS imagery as flight guidance. The FAA does not intend for 

the EFVS imagery to be used either as a means of flight guidance/instrument guidance, or as the 

substitution for the outside view prior to DA/DH or MDA.

c. Criteria to determine EFVS is of the kind and design appropriate to the following 

functions:

1. Presenting an enhanced view that would aid the pilot during the approach.

2. Displaying an image that the pilot can use to detect and identify the 

“visual references for the intended runway” required by 14 CFR 91.176(b)(3) to continue the 

approach with vertical guidance to 100 feet height above touchdown (HAT).

3. Depending on the atmospheric conditions and the particular visual 

references that happen to be distinctly visible and identifiable in the EFVS image, these two 

functions (found in paragraphs 3-1,a,1 and 3-1, a, 2) would support its use by the pilot to visually

monitor the integrity of the approach path.

4. Compliance does not affect the applicability of any of the requirements in 

the operating regulations (such as 14 CFR parts 91, 121, 125 and 135). The EFVS does not 

change the approach minima prescribed in the standard instrument approach procedure being 

used; published minima still apply. (Refer to AC 90-106A for additional information) 

3-2. Features.

a. The EFVS can be used as a supplemental device to enhance the pilot's situational 

awareness during any phase of flight or operation in which its safe use has been established.

b. An EFVS image can provide an enhanced image of the scene that can compensate 

for any reduction in the clear outside view of the visual field framed by the HUD combiner. The 

pilot must be able to use this combination of information seen in the image, and the natural view 

of the outside scene seen through the image, as safely and effectively as the pilot would use a 

14 CFR 2X.773-compliant pilot compartment view without an EVS image.

c. 14 CFR 2X.1301, Equipment: Function and installation, and 25.1309, Equipment, 

systems, and installations, address certain image characteristics, installation, demonstration, and 

system safety.

1. Image characteristics criteria include:

(a) Resolution

(b) Luminance

(c) Luminance uniformity
MM/DD/YYYY AC 20-167A

A3-2

(d) Low level luminance

(e) Contrast variation

(f) Display quality

(g) Display dynamics (for example, jitter, flicker, update rate, and lag) 

and

(h) Brightness controls

2. Installation criteria address:

(a) Visibility and access to EFVS controls

(b) Integration of EFVS in the cockpit

3-3. Demonstration.

The EFVS demonstration criteria address the flight and environmental conditions that should 

to be covered.

a. The EFVS imagery on the HUD must not degrade the safety of flight, nor 

interfere with the effective use of outside visual references for required pilot tasks, during any 

phase of flight in which it is used.

b. To avoid unacceptable interference with the safe and effective use of the pilot 

compartment view, the EFVS device should meet the following criteria:

1. The EFVS design should minimize unacceptable display characteristics or 

artifacts (for example, noise, “burlap” overlay, running water droplets) that obscure the desired 

image of the scene, impair the pilot's ability to detect and identify visual references, mask flight 

hazards, distract the pilot, or otherwise degrade task performance or safety.

2. Control of EFVS display brightness should be sufficiently effective, in 

dynamically changing background (ambient) lighting conditions, to prevent full or partial 

blooming of the display that would distract the pilot, impair the pilot's ability to detect and 

identify visual references, mask flight hazards, or otherwise degrade task performance or safety. 

If automatic control for image brightness is not provided, it should be shown that a single manual 

setting is satisfactory.

3. A readily accessible control, that does not require the removal of the 

pilot’s hands from the primary flight controls, must be provided that permits the pilot to 

immediately deactivate and reactivate display of the EVS image on demand.

4. The EFVS image on the HUD should not impair the pilot's use of 

guidance information nor degrade the presentation and pilot awareness of essential flight 

information displayed on the HUD, such as alerts, airspeed, attitude, altitude and direction, 

approach guidance, windshear guidance, TCAS resolution advisories, and unusual attitude 

recovery cues.

5. The EFVS image should be sufficiently aligned and conformal to both the 

external scene and conformal HUD symbology so as not to be misleading, cause pilot confusion, 

or increase workload.
MM/DD/YYYY AC 20-167A

A3-3

6. The safety and performance of the pilot tasks associated with the use of 

the pilot compartment view must not be degraded by the display of the EFVS image. Pilot tasks 

that must not be degraded by the EFVS image include:

(a) Detection, accurate identification, and maneuvering, as necessary, 

to avoid traffic, terrain, obstacles, and other hazards of flight.

(b) Accurate identification and use of visual references required for 

every task relevant to the phase of flight.

7. Compliance with these criteria does not affect the applicability of any of 

the requirements in the operating regulations (for example, 14 CFR parts 91, 121, 125 and 135). 

The criteria must be of a kind and design appropriate to the following functions:

(a) Present an image to aid the pilot during the approach.

(b) Display an image that the pilot can use to detect and identify the 

"visual references for the intended runway" required by 14 CFR 91.176 to continue the approach

to 100 feet height above touchdown (HAT) under EFVS I operations or all the way to touchdown 

and rollout under EFVS II operations. Appropriate limitations should be included in the 

Operating Limitations section of the Airplane Flight Manual to prohibit the use of the EFVS for 

functions not found to be acceptable.

c. In addition to the sensor imagery, at least the following specific aircraft flight 

information must be displayed:

1. Airspeed

2. Vertical speed;

3. Aircraft attitude;

4. Heading;

5. Altitude;

6. Command guidance as appropriate for the approach to be flown;

7. Path deviation indications;

8. Flight path vector; and

9. Flight path angle reference cue.

10. Radio altitude (For systems seeking EFVS II credit)

11. Flare Cue (For systems seeking EFVS II credit)

d. Head-Up Display. An EFVS used to conduct operations under 14 CFR 91.176, 

121.651, 125.381, and 135.225 must have an FAA type design approval, or for a foreignregistered aircraft, the EFVS must comply with all of the EFVS requirements of the U.S. 

regulations. Under 14 CFR 91.176, an EFVS is an installed airborne system which includes:

1. The display element, which is a HUD or an equivalent display, that 

presents the features and characteristics required by the regulations such that they are clearly 

visible to the pilot flying in his or her normal position and line of vision looking forward along 

the flight path.
MM/DD/YYYY AC 20-167A

A3-4

2. Sensors that provide a real-time image of the forward external scene 

topography, as described above.

3. Computers and power supplies.

4. Indications.

5. Controls.
MM/DD/YYYY AC 20-167A

A4-1

Appendix 4. Sample EFVS I Flight Test Considerations

4-1. General Flight Test Considerations.

a. The objectives of the flight test program are to ensure that the system performs its 

intended function when installed, and to demonstrate that the EFVS is operationally acceptable 

and safe. The objectives of the flight test program are not to quantitatively measure the detection 

performance of the sensor.

b. At the end of the flight test program, the EFVS I should have demonstrated it is 

capable of imaging the required visual references before they are visible out the window using 

natural vision. The EFVS should enable descent below DA/DH or MDA using enhanced flight 

visibility when visual references would not otherwise be visible using natural vision at an 

altitude no lower than DA/DH or MDA.

c. The combination of the EFVS I imagery with the HUD symbology and the 

relationship between the two in terms of brightness and contrast is a critical issue with respect to 

the installation; therefore, for the purpose of certification flight testing, the environmental 

conditions chosen should be such that these parameters are adequately evaluated.

d. Environmental conditions should be chosen to exercise both the automatic and 

manual control of items such as brightness, contrast, and gain, and any other parameter that 

affects the image displayed to the pilot.

4-2. Minimum Flight Test Conditions Observed.

a. Testing should include an appropriate number of fault-free approaches (see note 

below) in as many of the conditions listed below as practicable and as applicable. Past 

experience has shown that more than 50 fault-free approaches to demonstrate than an EFVS 

adequately performs its intended function. The list below should be assessed against the specific 

sensor type. Additional test conditions can be specified.

1. Night VFR conditions over various topography (urban, rural, snow 

covered, etc.).

2. Day and night IFR conditions over various topography.

3. Representative levels of rainfall.

4. Representative levels of snowfall.

5. Representative levels of fog.

6. Haze

7. Representative sun angles.

8. Representative airport lighting configurations.

9. Representative airport/runway surface conditions (dry, wet, standing 

water, snow cover).

10. Representative thermal crossover conditions.
MM/DD/YYYY AC 20-167A

A4-2

11. Representative crosswind and off-set approach course conditions 

regarding lateral FOR.

12. Representative runway surface types (dirt, asphalt, concrete, etc.).

13. Representative adjacent surfaces types (dirt, asphalt, concrete, etc.).

14. Representative vertical path.

Note: A successful go-around due to lack of either enhanced vision from the 

DH/DA or natural vision at 100 ft above TDZE, does not constitute a faulted 

approach. A faulted approach is if:

1. HUD or EFVS I failure has occurred.

2. At 100 ft above TDZE the indicated airspeed, heading, or attitude are not 

satisfactory for a normal flare and landing, due to a confusing or misaligned EFVS I image.

3. At 100 ft above TDZE the aircraft is not positioned so that the cockpit is 

within, and tracking so as to remain within, the lateral confines of the runway extended.

4. Due to a confusing or misaligned image, the touchdown will be too short 

or too long.

5. The EFVS I image degrades the fly-ability of the display such that a 

successful approach to DA/DH or MDA/MDH is not possible.

4-3. Test Points

Testing should include all phases of flight for which the applicant seeks approval of the system. 

In addition to the success criteria for approaches, the EFVS I minimum performance standards 

require the assessment of the HUD/EFVS I display when used in conjunction with the flight 

instrumentation required in 14 CFR 91.176 and listed in chapter 4, paragraph 4-5.a.3 of this AC. 

The following evaluations should be performed in representative configurations. (The pilot 

evaluation matrix is at the end of this appendix.)

4-4. Evaluation During Taxi

a. Assess EFVS I/HUD combination while taxiing and making identification of 

objects on runways, taxiways, parking aprons.

b. Verify the use of EFVS I does not cause confusion or misleading information 

when viewing through the HUD/EVS all types of airport runway, taxiway, obstruction, and 

barrier lighting, marking and signage as well as the navigation, taxi, and landing lights of other

aircraft.

c. Verify the HUD combiner, with the image displayed, does not significantly alter 

the color perception of the external scene.

d. Assess lack of burn-in or blooming from high intensity heat sources such as 

operating (running) engines, etc.

4-5. Take off Evaluation

a. Ensure correct pitch angle is achieved using HUD pitch reference target.
MM/DD/YYYY AC 20-167A

A4-3

b. Verify symbology in EFVS I mode is clear, visible and does not cause overcontrol or oscillations in acquiring and maintaining the required ground track.

c. Confirm the HUD with EFVS I provides the pilot with a quick-glance (instant) 

sense of flight parameters.

d. Assess the transition to different selected vertical modes.

e. Evaluate the EFVS I image during the take off roll and throughout the climb 

segment, against the attributes listed in the pilot evaluation matrix.

4-6. Climb and Descent and Lateral Modes Evaluation

a. Climb, descent, and lateral modes should be evaluated in day and night IMC and 

VMC to assess HUD/EFVS I compatibility.

b. During vertical and lateral guidance maneuvers, evaluate the EFVS I image 

against the attributes listed in the pilot evaluation matrix.

4-7. Instrument Approaches.

During any instrument approach for which approval is sought, HUD/EFVS I compatibility

should be evaluated against the attributes listed in the pilot evaluation matrix.

4-8. Flare Landing and Go Around

a. While using EFVS I during final approach and through the flare (below 50 ft), 

touchdown roll or go-around, assess the transition to natural vision and compatibility of the 

guidance when following the HUD/EFVS I flight cues.

b. Confirm landing rollout information, if provided in the display, is sufficiently

visible to the pilot and does not cause over-control or oscillations in acquiring and maintaining 

the required ground track.

c. Throughout the approach guidance maneuvers, evaluate the EFVS I image against 

the attributes listed in the pilot evaluation matrix.

4-9. Copilot Monitor

a. A copilot monitor is not required by the FAA for operations within the United 

States. However, if one is installed, the applicant should assess the ergonomic aspects of the 

image on the copilot’s EFVS I monitor.

1. Verify satisfactory display of imagery in all lighting and environmental 

conditions and that dimming controls of the display are adequate.

2. If the display has dual purposes, verify the means of switching the display

to being the EFVS I monitor and back is satisfactory and clearly evident.

3. Verify no flicker and/or jitter in the display.

4. Verify no objectionable glare or reflections are generated by the display or 

are visible in the display.

5. Verify the co-pilot’s use of the EFVS I monitor does not require undue 

head/body movement away from his/her normal scan pattern or his/her normal seated position.

4-10. Failure Cases.
MM/DD/YYYY AC 20-167A

A4-4

Failure cases to support the FHA should be assessed as required, for example, uncommanded full 

image brightness, misaligned image, frozen image, etc. in addition to the approaches required in 

this appendix.

4-11. Ice Protection System Evaluation

a. If the EFVS I sensor installation has ice protection capability, the EFVS I image 

must be evaluated with the ice protection on and off in representative environmental conditions.

b. Icing of the sensor fairing/radome must be appropriately assessed in accordance 

with the certified flight envelope.

4-12. Evaluation Matrix.

a. Table 6 contains the pilot’s evaluation matrix. The evaluation matrix should be 

used to support the testing described in this appendix.

Table 6. EFVS I Evaluation Matrix

A Confirm crew workload is not adversely affected by the HUD/EFVS I installation. 

B Verify no adverse physiological effects from using the HUD/EFVS I (for 

example, fatigue, eye strain).

C Verify HUD/EFVS I symbology is visible within pilot Field of View (FOV) 

(When viewed by both eyes from any off-center position within eye box, nonuniformities should not produce perceivable differences in binocular view).

D Verify no jitter or flicker of HUD/EFVS I symbology/image.

E Verify the EFVS I image does not have noise, local disturbances or artifacts that 

distract from the use of the system.

F If HUD symbology has been modified to accommodate the EFVS I image, assess 

HUD guidance and ensure that introduction of EFVS I does not induce lag in 

control symbols inducing PIO.

G Verify the system is not adversely affected by aircraft maneuvering or changes in 

attitudes encountered during the referenced environmental conditions.

H Ensure the required flight and navigation functions applicable for the phase of 

flight being evaluated are clearly displayed on the HUD with no unacceptable 

occlusions during testing.

I Verify the total data presented by the EFVS I imagery and HUD symbology does 

not over clutter the HUD combiner display area.

J Assess the degree of obscuration of the pilot’s outside view or field of view 

through the cockpit window as a result of EFVS I imagery and HUD symbology.
MM/DD/YYYY AC 20-167A

A4-5

K Confirm the pilot’s ability to detect hazards, maneuver, avoid traffic, terrain or 

other obstacles, is not impaired or degraded by the display of EFVS I imagery.

L Confirm there is no discrepancy between the conformal HUD symbols, sensor 

image, and the outside view through the windshield.

M Verify outside visibility as viewed through combiner sensor imagery is adequately 

aligned and conformal to the external scene and HUD symbology.

N Confirm the EFVS I imagery does not obscure the desired imagery of the scene, 

impair the pilot’s ability to detect and identify visual references, mask flight 

hazards, or distract the pilot.

O Assess the ease of operating the HUD with the sensor image displayed, during 

aircraft maneuvers and change in attitude, encountered in normal operations.

P Determine whether there is any glare or reflection that could interfere with the 

EFVS I image either in day or night lighting conditions.

Q Determine if any impairment is experienced in the ability to use the display due to 

visible external surfaces within the HUD.

R Determine whether the sensor image displayed on the HUD combiner 

objectionably impairs the pilot compartment view.

S Assess impact of water droplets running across the sensor window to ensure that it 

does not distract the pilot or degrade his/her task performance or safety.

T Verify identification of approach lights, runway threshold, touchdown zone etc. as 

per 14 CFR 91.176(b)(3).

U Confirm the HUD EFVS I image is suitable and performs its intended function.

V Confirm the sensor image on the co-pilot’s display (if installed) is useable and 

performs its intended function.

W Evaluate the EFVS I image during the takeoff roll and throughout the climb 

segment, against the attributes listed in the attached pilot evaluation matrix. 

X During vertical and lateral guidance maneuvers evaluate the EFVS I image against 

the attributes listed in the attached pilot evaluation matrix. 
MM/DD/YYYY AC 20-167A

A5-1

Appendix 5. Sample Flight Test Considerations for EFVS II

5-1. General Flight Test Considerations.

a. The objectives of the flight test program are to ensure that the system performs its 

intended function when installed, and to demonstrate that the EFVS II is operationally acceptable 

and safe. The objectives of the flight test program are not to quantitatively measure the detection 

performance of the sensor.

b. The flight test program should demonstrate that the EFVS II is capable of 

providing enhanced flight visibility that is no less than the visibility required by the instrument 

approach, in conditions where actual flight visibility is no less than the visibility required by the 

instrument approach. The EFVS II flight demonstrations should prove that the system provides a 

satisfactory view of the required visual references for descent below DA/DH even when they are 

not visible using natural vision. The EFVS II should enable the pilot to complete the instrument 

approach, landing, and rollout to a safe taxi speed using enhanced flight visibility when visual 

references would not otherwise be sufficiently visible using natural vision.

c. The flight test should demonstrate that the EFVS II display of imagery and HUD 

symbology is satisfactory, so that both elements of information are readable and usable without 

mutual interference. The flight test should demonstrate that the brightness levels of the imagery

and the symbology can be effectively controlled and provide satisfactory contrast between two. 

Since flight deck and external light levels can affect the readability of the EFVS II display and 

can change significantly throughout the approach and landing operation, the flight test should 

demonstrate that control of display brightness in dynamic conditions does not require excessive 

workload for the pilot.

d. Environmental conditions should be chosen to exercise both the automatic and 

manual control of items such as brightness, contrast, and gain, and any other parameter that 

affects the image displayed to the pilot.

5-2. Minimum Flight Test Conditions Observed.

a. Testing should include an appropriate number of fault-free approaches and 

landings in as many of the conditions listed below as practicable and as applicable. The 

applicant should plan for no less than 50 fault free approaches and landings, of which at least 5 

approaches will be needed to confirm satisfactory go-around performance. A sufficient number 

of approaches will be needed, with visibility conditions between 2400ft RVR or less and 1000ft 

RVR, to demonstrate that the EFVS II can provide at least 2400 ft of enhanced flight visibility

and enable the complete low visibility operation. The applicant and the FAA will agree on the 

minimum number of such approaches, but the number may change depending on demonstration 

results. The following list should be assessed against the EFVS II Sensor(s), intended use and 

the specific installation. Additional tests may be specified. The environmental conditions to be 

tested must be agreed to by the FAA.

1. Night VFR conditions over various topography (urban, rural, snow 

covered, etc.).

2. Day and night IFR conditions over various topography.

3. Representative levels of rainfall.
MM/DD/YYYY AC 20-167A

A5-2

4. Representative levels of snowfall.

5. Representative levels of fog.

6. Haze.

7. Representative sun angles.

8. Representative airport lighting configurations.

9. Representative airport/runway surface conditions (dry, wet, standing 

water, snow covered).

10. Representative thermal crossover conditions.

11. Representative wind conditions (e.g., crosswind, headwind, tailwind) and 

off-set conditions regarding lateral field of regard.

12. Representative runway surface types (dirt, asphalt, concrete, etc.).

13. Representative adjacent surfaces types (dirt, asphalt, concrete, etc.).

14. Representative runway widths.

15. Representative approach procedures and vertical approach angles.

16. Representative runway slopes (within the aircraft limitations).

b. A faulted approach occurs anytime the pilot is unable to complete a safe and 

successful approach, landing, rollout, and turnoff within the operational performance parameters 

detailed in Appendix 4, or within additional operational performance standards as may be 

required by the certifying authority. However, a faulted approach does not occur due to the lack 

or loss of enhanced visibility due to the atmosphere, so long as a successful missed approach or 

rejected landing is executed. A faulted approach also does not occur due to ATC intervention, 

interference from other aircraft, interference from ground vehicles or persons, interference from 

animals (including birds), or any other reason not relating directly to the EFVS.

5-3. Test Points.

a. Testing should include all phases of flight in which EFVS II operation will be 

permitted, approach types, approach course geometries, and aircraft configurations for which the 

applicant seeks approval of the system. In addition to the success criteria for the approach, 

landing and rollout, the EFVS II minimum performance standards require the assessment of the 

HUD/EFVS display when used in conjunction with the head up flight indications required in 14 

CFR 91.176 and listed in chapter 4, paragraph 4-5.a.3 of this AC. For effective post-flight 

analysis and evaluation of the results, past experience has shown that time-stamped video of 

exactly what is displayed on the HUD are recommended.

b. The test program should demonstrate that the EFVS II image, with superimposed 

flight symbology, does not mislead, distract or jeopardize the safety of the landing and rollout. 

Without requiring exceptional pilot skill, alerting, strength or workload, the image/symbology

should allow and provide the visual cues for the pilot to perform:

1. Speed control within +10/-5 knots of the approach speed, whether

manually controlled or with auto-throttle, as proposed by the applicant, up to the point where the 

throttles are retarded for landing.
MM/DD/YYYY AC 20-167A

A5-3

2. A smooth transition through flare to landing.

3. Approach, flare and landing at a normal sink rate for the aircraft.

4. Lateral touchdown performance shall be demonstrated to be the equivalent 

or better to that achieved in visual operations for the specific aircraft. Longitudinal touchdown 

performance shall be demonstrated within the first 1/3, or the first 3000 ft, of the runway, 

whichever is more restrictive, and demonstrated to be equivalent or better to that achieved in 

visual operations for the specific aircraft.

5. Prompt and predictable correction of any lateral deviation away from the 

runway centerline to smoothly intercepted the centerline.

6. Touchdowns with a bank angle that is not hazardous to the airplane.

7. Demonstrated performance of the installed EFVS II at the representative 

RVR/visibility, as described in this document, will determine any additional limitations (for 

example, crosswind and offset).

8. A normal de-rotation.

9. Satisfactory and smooth control of the airplane from touchdown to a safe 

taxi speed.

10. Satisfactory and smooth control of the path of the airplane along the 

runway centerline through rollout to a safe taxi speed.

11. A safe go around anytime including touchdown in all configurations to be 

certified.

5-4. Evaluation During Taxi

a. Assess EFVS/HUD combination while taxiing and making identification of 

objects on runways, taxiways, parking aprons.

b. Verify that the use of EFVS II does not cause confusion or misleading 

information when viewing through the HUD/EFVS II appropriate types of airport runway, 

taxiway, obstruction, and barrier lighting and signage as well as the navigation, taxi, and landing 

lights of other aircraft.

c. Verify the HUD combiner with the image displayed does not significantly alter 

the color perception of the external scene.

d. Assess the impact of burn-in or blooming (if applicable) on the EFVS II image 

from high intensity heat sources such as running engines, stationary lights, etc.

5-5. Take off Evaluation.

a. Ensure correct pitch angle is achieved using HUD pitch symbology.

b. Verify symbology in EFVS II mode is clear, visible and does not cause overcontrol or oscillations in acquiring and maintaining the required ground track.

c. Confirm that the HUD with EFVS II provides the pilot with a quick-glance 

(instant) sense of flight parameters.

d. Assess the transition to different selected vertical modes.
MM/DD/YYYY AC 20-167A

A5-4

e. Evaluate the EFVS II image during the take off roll and throughout the climb 

segment, against the attributes listed in the pilot evaluation matrix.

5-6. Climb and Descent and Lateral Modes Evaluation.

a. Climb, descent and lateral modes should be evaluated in day and night IMC and 

VMC to assess HUD/EFVS II compatibility.

b. During vertical and lateral guidance maneuvers, evaluate the E(F)VS image 

against the attributes listed in the pilot evaluation matrix.

5-7. Instrument Approaches to the DA(H)

a. During any instrument approach for which approval is sought, HUD/EFVS II

compatibility should be evaluated against the attributes listed in the pilot evaluation matrix.

b. Final approach course offsets greater than 3 degrees require further flight test 

evaluation. The maximum allowable final approach course offset is to be established by flight 

test. These tests should include the factors related to the offset, such as the HUD/EFVS II field 

of view, crosswinds, and the maximum drift angle possible for a conformal flight path vector. 

Since 14 CFR 91.176 permits EFVS to touchdown for approaches which could be offset up to 15 

degrees, flight test evaluation should factor this offset into potential limitations and airworthiness 

approvals.

5-8. Final Approach from the DA/DH, Flare, Landing and Rollout to Safe Taxi Speed.

a. While using EFVS II during an enhanced visual final approach and through the 

flare (below 50ft), touchdown, rollout and turn-off, assess the performance of the EFVS II image 

and displayed symbology against the attributes listed in the pilot evaluation matrix.

b. Confirm that a landing and rollout to a safe taxi speed that is primarily 

performance based on the EFVS II image and displayed symbology does not cause over-control 

or oscillations in acquiring and maintaining the required ground track.

5-9. Rejected Landing

Confirm that at any time during the EFVS II based approach between DA/DH and touchdown, a 

safe rejected landing can be conducted.

5-10. Pilot Monitoring (PM) Display.

a. Verify the display is located within the maximum primary field of view of the 

pilot monitoring and any symbology displayed should not adversely obscure the sensor imagery 

of the runway environment.

b. Verify satisfactory display of imagery in all lighting and environmental conditions 

and that dimming controls of the display are adequate.

c. If the display has dual purposes, verify the means of switching the display to 

being the EFVS II monitor and back is satisfactory and clearly evident.

d. Verify that the pilot monitoring use of the PM display monitor does not require 

undue head/body movement away from his/her normal scan pattern or his/her normal seated 

position.
MM/DD/YYYY AC 20-167A

A5-5

e. Verify the PM display provides a conformal image with the visual scene over the 

range of aircraft attitudes and wind conditions for each mode of operation. The PM’s display

should be shown to be acceptable for the pilot monitoring to see and identify visual references 

and to verify that all visual requirements for the approach and landing are satisfied.

5-11. Failure Cases.

Failure cases to support the FHA shall be assessed and tested as required (e.g. uncommanded full 

image brightness, misaligned image, frozen image, failed image, etc.) during the approaches 

required in this appendix.

5-12. Ice Protection System Evaluation.

a. If the EFVS II sensor installation has ice protection/de-misting capability, the 

EFVS II image should be evaluated with the ice protection/de-misting on and off in 

representative environmental conditions.

b. Icing of the sensor fairing should be appropriately assessed in accordance with the 

aircraft’s certified flight envelope.

5-13. Evaluation Matrix

Table 7 below is the test evaluation matrix that should be used to support the testing described 

above.

Table 7. EFVS II Evaluation Matrix

A Confirm that crew workload is not adversely affected by the HUD/EFVS II installation.

B Verify no adverse physiological effects from using the HUD/EFVS II (e.g. fatigue, eye 

strain).

C Verify HUD/EFVS II symbology is visible within pilot Field of View (FOV). (When 

viewed by both eyes from any off-center position within eye box, non-uniformities 

shall not produce perceivable differences in binocular view).

D Verify no jitter or flicker of HUD/EFVS II symbology/image.

E Verify that the EFVS II image does not have noise, local disturbances or artifacts that 

distract from the use of the system.

F If HUD symbology has been modified to accommodate the EFVS II image, assess 

HUD guidance and ensure that introduction of EFVS II does not induce lag in control 

symbols inducing PIO.

G Verify the system is not adversely affected by aircraft maneuvering or changes in 

attitudes encountered during the referenced environmental conditions.

H Ensure that the required flight and navigation functions applicable for the phase of 

flight being evaluated are clearly displayed on the HUD with no unacceptable 

occlusions during testing.
MM/DD/YYYY AC 20-167A

A5-6

I Verify that the total data presented by the EFVS II imagery and HUD symbology does 

not over clutter the HUD combiner display area.

J Assess the degree of obscuration of the pilots outside view or field of view through the 

cockpit window as a result of EFVS II imagery and HUD symbology.

K Confirm that the pilot’s ability to detect hazards, maneuver, avoid traffic, terrain or 

other obstacles, is not impaired or degraded by the display of EFVS II imagery.

L Confirm that there is no discrepancy between the conformal HUD symbols, sensor 

image and the outside view through the windshield.

M Verify that outside visibility as viewed through combiner sensor imagery is adequately 

aligned and conformal to the external scene and HUD symbology.

N Confirm that the EFVS II imagery does not obscure the desired imagery of the scene, 

impair the pilot’s ability to detect and identify visual references, mask flight hazards or 

distract the pilot.

O Assess the ease of operating the HUD with the sensor image displayed, during aircraft 

maneuvers and change in attitude, encountered in normal operations.

P Determine whether there is any glare or reflection that could interfere with the EFVS II

image external surfaces within the HUD.

Q Determine if any impairment is experienced in the ability to use the display due to 

visible external surfaces within the HUD.

R Determine whether the sensor image displayed on the HUD combiner objectionably

impairs the pilot compartment view.

S Assess impact of water droplets running across the sensor window to ensure that it 

does not distract the pilot or degrade his/her task performance or safety.

T Verify identification of approach lights, runway threshold, touchdown zone etc. as per 

14 CFR 91.176(a)(3).

U Confirm the sensor image on the copilot’s display (if installed) is useable and performs 

its intended function.

V Confirm the sensor image on the copilot’s display (if installed) is useable and performs 

its intended function.

W Evaluate the EFVS II image during the take off roll and throughout the climb segment, 

against the attributes listed in the attached pilot evaluation matrix.

X During vertical and lateral guidance maneuvers evaluate the EFVS II image against the 
MM/DD/YYYY AC 20-167A

A5-7

attributes listed in the attached pilot evaluation matrix.

Y Confirm that the EVS provides the correct and appropriate visual cues for the pilot to 

perform the required stabilized approach from the DA(H).

Z Confirm that approach speed can be controlled within +10/-5kts, both with and without 

auto-throttle if fitted, up to the point where the throttles are retarded for landing.

AA Confirm that the EVS provides the correct visual cues for the pilot to perform a smooth 

transition through flare to landing.

AB Confirm that the EVS provides the correct visual cues for the pilot to perform a flare 

and landing with a normal sink rate.

AC Confirm that the EVS provides the correct visual cues to always allow a consistent 

touchdown in the defined touchdown zone.

AD Confirm that the EVS provides the correct visual cues to allow a consistent touchdown 

with a bank angle that is not hazardous to the airplane.

AE Confirm that the EVS provides the correct the correct visual cues to allow satisfactory

and smooth control of the airplane from touchdown to a safe taxi speed.

AF Confirm that EVS provides the correct visual cues to allow prompt and predictable 

correction of any lateral deviation away from the runway centerline to smoothly

intercept the centerline.

AG Confirm that the EVS provides the correct visual cues to allow prompt and predictable 

correction of any lateral deviation away from the runway centerline to smoothly

intercept the centerline.

AH Confirm that the EVS provides the correct visual cues to allow satisfactory and smooth 

control of the path of airplane along the runway centerline through rollout to a safe taxi 

speed.
MM/DD/YYYY AC 20-167A

A6-1

Appendix 6. Sample Airplane Flight Manual (AFM) Supplement

Note: Appendix 6 presents a sample for the AFM supplement for STC installations. This 

example may not be entirely applicable to airplane manufacturers when SVS, EVS, CVS, or 

EFVS are approved with the type certificate. The ACO will assist the applicant in developing an 

appropriate Rotorcraft Flight Manual Supplement (RFMS).

Installation Center/Repair Station Model XXX EVS/SVS/EFVS 

123 Fourth Street Vision System 

Anytown, USA 

 FAA APPROVED AIRPLANE FLIGHT MANUAL SUPPLEMENT

ABC MODEL XXX YYY VISION SYSTEM

 AIRPLANE MAKE: 

AIRPLANE MODEL: 

AIRPLANE SERIAL NO.: 

REGISTRATION NO.: 

This document must be carried in the airplane at all times. It describes the operating procedures 

for the ABC Model XXX YYY vision system when it has been installed in accordance with 

<manufacturer's installation manual number and date>. 

For airplanes with an FAA Approved Airplane Flight Manual, this document serves as the FAA 

Approved ABC Model XXX YYY Flight Manual Supplement. For airplanes that do not have an 

approved flight manual, this document serves as the FAA Approved ABC Model XXX YYY 

Supplemental Flight Manual. 

The information contained herein supplements or supersedes the basic Airplane Flight Manual 

dated <insert date> only in those areas listed herein. For limitations, procedures, and 

performance information not contained in this document, consult the basic Airplane Flight 

Manual. 

 FAA APPROVED 

____________________ 

Title 

Office 

Federal Aviation Administration 

City, State
MM/DD/YYYY AC 20-167A

A6-2

SAMPLE AIRPLANE FLIGHT MANUAL (Continued)

Installation Center/Repair Station Model XXX EVS/SVS/EFVS 

123 Fourth Street Vision System 

Anytown, USA

Table of Contents

Section...............................................Page

 1 General.............................................< > 

 2 Limitations........................................< > 

 3 Emergency/Abnormal Procedures....< > 

 4 Normal Procedures...........................< > 

 5 Performance......................................< > 

 6 Weight and Balance..........................< > 

 7 System Description...........................< > 

FAA Approved Page <> of <> 

Date: ________ 
MM/DD/YYYY AC 20-167A

A6-3

SAMPLE AIRPLANE FLIGHT MANUAL (Continued)

Installation Center/Repair Station Model XXX EVS/SVS/EFVS 

123 Fourth Street Vision System

Anytown, USA 

SECTION 1 - GENERAL

<Include the appropriate statement to describe the equipment capability: >

EVS: The installed ABC Enhanced Vision System meets with AC 20-167A performance criteria 

for <situation awareness>.

SVS: The installed ABC Synthetic Vision System meets with AC 20-167A performance criteria 

for <situation awareness>.

EFVS I: The installed EFVS has been demonstrated to meet the criteria for AC 20-167A for 

EFVS I to be used for DA/DH or MDA down to 100 feet HAT.

During certification flight test, the lowest visibility and maximum final approach course offset 

angle at which the installed EFVS was demonstrated to be used in lieu of natural vision to 

descend below DA/DH or MDA and complete a landing in accordance with 14 CFR 91.176(b) 

was < insert RVR value or SM value > and < insert angle in degrees >, respectively.

EFVS II: The installed EFVS II has been demonstrated to meet the criteria for AC 20-167A for 

EFVS II to be used for instrument approach and landing operations that rely on sufficient 

visibility conditions to enable unaided rollout and to mitigate for loss of EFVS function. An 

EFVS that meets the certification criteria for EFVS II also meets the criteria for EFVS I.

During certification flight test, the lowest visibility and maximum final approach course offset 

angle at which the installed EFVS was demonstrated to be used in lieu of natural vision to 

descend below DA/DH or MDA and complete a landing in accordance with 14 CFR 91.176(b) 

was < insert RVR value or SM value > and < insert angle in degrees >, respectively.

SECTION 2 - LIMITATIONS

1. The ABC Model XXX YYY Quick Reference Guide, P/N <insert part number>, dated 

<insert date> (or later appropriate revision) must be immediately available to the flight crew 

whenever navigation is predicated on the use of the system. 
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2. The system must utilize software version <insert version identification>. 

3. A valid and compatible database must be installed and contain current data.

4. <Specify any additional limitations applicable to the particular installation.>

FAA Approved Page <> of <> 

Date: ________ 

SECTION 3 - EMERGENCY/ABNORMAL PROCEDURES

EMERGENCY PROCEDURES

No Change

ABNORMAL PROCEDURES 

1. If ABC Model XXX YYY vision system information is not available or invalid, utilize 

remaining operational navigation equipment as appropriate. 

2. If Loss of Integrity Monitoring message is displayed, revert to an alternate means of 

navigation appropriate to the route and phase of flight or periodically cross-check the GPS 

guidance to other, approved means of navigation.

SECTION 4 - NORMAL PROCEDURES

1. Normal operating procedures are outlined in the ABC Model XXX YYY Pilot's Guide. 

2. System Annunciators <applicable to installations with external annunciators>

3. System Switches <applicable to installations with external switches> 
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4. Pilot's Display <describe the pilot's display(s)>

5. Flight Director/Autopilot Coupled Operation <describe any procedures for integrated flight 

director and/or autopilot system(s)> 

6. <include any other normal operating procedures as necessary>

FAA Approved Page <> of <> 

Date: ________ 
MM/DD/YYYY AC 20-167A

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SECTION 5 - PERFORMANCE

No Change 

SECTION 6 - WEIGHT AND BALANCE

<Refer to revised weight and balance data, if applicable.> 

SECTION 7 - SYSTEM DESCRIPTION

<Provide a brief description of the system, its operation, installation, etc.>

FAA Approved Page <> of <> 

Date: ________
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Appendix 7. Installation of Enhanced Vision System and or/Synthetic Vision System on 

Rotorcraft

7-1. General.

This appendix provides guidelines for the installation of EVS and/or SVS installed in Rotorcraft 

as non-required safety enhancing equipment. To promote standardization installation of nonrequired safety enhancing equipment, the Rotorcraft Directorate published a policy memo to 

address a means of compliance for the installation of non-required safety enhancing equipment. 

Contact the FAA Rotorcraft Directorate for guidance. Also refer to AC 27-1B and AC 29-2C

for certification guidance.

7-2. Applicability.

There are unique aspects to rotorcraft that do not apply to fixed wing aircraft. Rotorcraft 

typically operate at altitudes much closer to the ground and obstacles than fixed-wing aircraft. 

Additionally, they are inherently unstable and, without a stabilization system, require hands-on 

control at all times accompanied by constant visual scans to keep them oriented correctly. There 

are advantages and disadvantages to presenting EVS or SVS information to the pilot. Particular 

issues of concern are the compelling nature of the display used in a VFR see-and-avoid 

environment, the presentation of misleading information relating to aircraft location relative to 

hazards (particularly in night operations), and the installation of EVS/SVS/CVS displays that 

interact with automated flight control systems and flight guidance systems.

7-3. Airworthiness Approval.

The Rotocraft Directorate has determined that installation of EVS/SVS/CVS on a primary flight 

display, either ADI or NAV display, requires ACO involvement through the STC process, under 

FAA Order 8900.1, Volume 4, Chapter 9 “Selected Field Approvals,” Figure 4-68, Major 

Alterations Job Aid. Installations on a primary flight display will involve human factors 

evaluations and flight test evaluations.

7-4. Design Considerations.

The FHA developed for the system should define the hazards of presenting misleading 

information to the pilot, and loss of an SVS/EVS feature. The system should be designed 

accordingly. The hazard classification will be based on display location, intended function of the 

system features, and phase of flight. The hazard classification of misleading information for 

SVS/EVS/CVS on the primary flight displays will be higher than the classification of misleading 

information on a display outside the pilot’s primary field of view. For example, the hazard 

classification of misleading information may be lower if the SVS/EVS/CVS is placed on 

ancillary displays not used for the display of flight information and not in the pilot’s primary

field of view. Additionally, see Appendix 8 of this AC for further guidance. However, the 

Rotorcraft Directorate does not accept “situation awareness only” information on primary flight 

displays (either PFD or MFD’s within the pilot’s primary field of view). Therefore the intended 

function of the SVS/EVS/CVS should be defined. If HTAWS or HTAWS-like features are 

incorporated, see TSO-C194 HTAWS
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Appendix 8. Additional Part 23 Considerations for Enhanced Vision System/or Synthetic 

Vision System for Situation Awareness Only

8-1. Introduction.

Synthetic vision may be so compelling that pilots may try to use it beyond the intended function. 

Current synthetic vision systems may not offer the depth/distance cueing necessary to be used for 

terrain avoidance. Another way of saying this is that error margins may still be too large to use 

any synthetic vision system alone. Current systems should be used with approved flight and 

navigation information. If other systems are not included to augment the synthetic vision system 

for terrain awareness, the applicant should show that the error margins due to field of view size, 

depth perception, resolution of the database used, resolution of the display, update rate of the 

display and any other factors are small enough that synthetic vision alone is adequate for terrain 

awareness in all flight conditions expected. Display size constraints may result in a 

“compressed” display that has the potential to cause misleading altitude and range estimation. In 

addition, cumulative errors from GPS, terrain databases, and barometric altimetry systems may

contribute to misleading distance and height cues. Adequate mitigation should be provided to 

avoid the effects of such hazards. Such mitigation may be incorporated in the design or may

include training or procedures to use other navigation sources. However, it is unwise to depend 

solely on Aircraft Flight Manual (AFM) limitations.

8-2. Terrain Alerting.

Any airplane equipment incorporating a synthetic vision system should also provide some type 

of terrain warning for pilots. The terrain warning feature should be incorporated on the 

Multifunction Display (MFD) or separate display unless the applicant can demonstrate that the 

feature is effective on the PFD. Synthetic vision systems on the PFD should provide adequate 

altitude and distance cues if used for terrain warning.

a. Applicants may use TSO-C151c, Class A, B, or C standards as applicable. 

Applicants may develop their own terrain warning system. However, the option of developing a 

terrain warning system is only available when there is not a specific carriage requirement for 

TAWS or HTAWS; it is not a substitute for any TAWS or HTAWS regulatory requirement. 

Applicants who want to develop their own terrain warning system should include:

1. A one-minute caution and 30-second warning if the airplane’s current 

flight path will collide with terrain or an obstacle.

2. Aural call-out for both the caution and the warning (CAUTION –

TERRAIN, TERRAIN; WARNING – TERRAIN, TERRAIN).

3. Terrain impact region highlighted on the moving map.

4. A safety margin or buffer of at least 100 feet for cumulative errors in both 

the GPS altitude and terrain database.

5. A terrain database/DEM developed using the criteria in RTCA DO-200A, 

“Standards for Processing Aeronautical Data,” September 28, 1998.
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6. The synthetic vision display must not provide any information that is in 

conflict with or incompatible with either the terrain warning or terrain awareness functions of the 

TAWS or HTAWS.

8-3. Moving Map Display that Corresponds to and Complements Synthetic Vision PFD 

Display.

a. Synthetic vision depictions on the PFD have the potential to provide pilots with 

enhanced terrain and landmark awareness during non-precision and precision approaches. 

However, the display may not provide depth perception and may not provide a field-of-view for 

pilots to know what is to the left and right of the display view area. When viewing the terrain on 

a limited field-of-view display, pilots may mistakenly infer the location of the aircraft relative to 

the terrain.

b. There should be a second, complementary plan view display. The second display

should depict the same terrain, obstacles, and features that appear on the PFDs synthetic vision

display. This complementary display mitigates the lack of depth perception and FOV limitations 

on the typical synthetic vision display. This display should be the navigation display, but it 

could also be an MFD or a third, separate display. Ideally, the TAWS OR HTAWS or terrain 

alerting system should be part of this display (unless incorporated into the PFD) so that 

hazardous terrain or obstacles are highlighted.

8-4. Minimums Audio Callout Capability.

Applicants are encouraged to incorporate either a pilot selectable or automatic altitude alert with 

audio callout to remind pilots they are approaching minimums. Pilots may “see” the runway

environment on their synthetic vision display and continue below minimums inadvertently

because they were so intent on following the approach guidance. This scenario is similar to 

pilots fixating on a flight director and descending below minimums. Alerting pilots that they are 

nearing minimums reduces the opportunity for this situation to occur.

8-5. Digital Evaluation Model (DEM) Resolution.

The DEM resolution is one factor that determines how well the synthetic vision terrain depiction 

will match the terrain environment. NASA experiments have shown that a terrain resolution of 

30-arc-seconds “rounds off” the terrain peaks and fills in valleys. This makes the terrain appear 

less hazardous for the peaks than it is and potentially reduces some safety benefit. Conversely, 

for the valleys, the terrain appears higher and is therefore conservative. The same set of NASA 

experiments pointed out that even though pilots preferred terrain created using higher resolutions 

(one and three-arc-seconds), a synthetic vision display using a 30-arc-second database could 

provide more situation awareness (and, therefore, safety) than the conventional instrument panel. 

Therefore, we had historically considered 30-arc-second resolution the minimum safety standard 

for synthetic vision displays. This allowed for the introduction of synthetic vision systems given 

the technology limitations. But technology has surpassed the need to allow as low a minimum 

resolution. New systems should meet 15 arc sec or better. Current systems do very well at twice 

the resolution minimum, but we want to encourage applicants to use the highest resolutions 

available in unclassified databases. Applicants may also consider using very high resolution 

databases near airports while reducing the resolution in the rest of the database. More 

importantly, applicants should clearly define the resolution and measuring units of the DEM used 
MM/DD/YYYY AC 20-167A

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by their synthetic vision system in the AFMS and the pilots’ handbooks so that pilots can 

understand any visual limitation caused by resolution limits.

Note: The DEM resolution needed on a synthetic vision display depends on the intended 

function of that display. Applicants need to consider how they are going to use the terrain 

database information for their synthetic vision display, and this information should be given to 

the FAA at the beginning of a synthetic vision certification program. Common elevation 

references are average elevation, maximum elevation, and sometimes, the elevation of the 

geometric center of the area. As post-spacing increases, the difference between the DEM value 

and the actual elevation of a point within a cell may differ significantly. The elevations used for 

a synthetic vision display should be conservative; use the highest elevation for a given cell. This 

concept is identical to the current sectional charts labeling the highest elevation in the given 

quadrangle (square sector) of latitude and longitude.

8-6. Aircraft Flight Manual Supplement (AFMS).

The AFMS should contain limitations for pilots on use of the applicant’s system. These 

limitations should be explained in detail. Warnings, cautions, and notes should also address the 

proper use and potential misuse of the display for terrain awareness and avoidance.

8-7. SVS Unusual Attitude Recovery.

Historically, the FAA required all but essential flight information is removed from the PFD in 

unusual attitudes. This “decluttering” was meant to aid pilots in recovering the aircraft. 

Therefore, the first synthetic vision systems removed the synthetic depiction and reverted to the 

traditional “blue-over-brown” display during unusual attitudes. Based on a past report, the FAA 

Civil Aeronautical Medical Institute (CAMI) observed little performance difference between 

recoveries with and without the synthetic depiction. Furthermore, there was a possibility pilots 

might be temporarily confused by the significant change to their primary attitude display. 

Therefore, applicants should consider leaving the synthetic vision depiction on the PFD for 

unusual attitude recovery. The SVS update rate will be evaluated in flight test against FAA 

Practical Test Standard maneuvers.

a. Some indication of both sky and ground should always be visible on the PFD for 

use in initiating unusual attitude recovery.

b. Pilots should be able to initiate a recovery toward the correct horizon and altitude 

within one second of recognition.

Note: For example, a test scenario could include climbing with a large mountain or 

plateau in the background into a stall condition or descending into rising terrain with decreasing 

airspeed into a stall condition.

c. The artificial horizon line and other attitude-relate symbology (for example, 

aircraft symbol and pitch ladder) should be very prominent and highly visible against all possible 

backgrounds and symbology, including the assignment of a level of priority over other 

symbology on the display commensurate with its importance.

8-8. Pilot Evaluation.
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There are hundreds of variables that can distinguish one display system from another. 

Depending on the design implementation, a synthetic vision system might not provide a safety

improvement. Because of the number of variables, a thorough FAA pilot evaluation will be 

necessary for the first implementation of any synthetic vision display system. Less FAA 

involvement may be possible on subsequent installations or system upgrades. Often, it is useful 

to gather subjective pilot assessments of the synthetic vision displays. Questionnaires used with 

flight evaluations and/or simulation are good tools to use for pilot assessment, but they need to 

be specific rather than merely solicit general impressions. Accepted and proven evaluation 

protocol, measures, and scales should be used where applicable to ensure the integrity of the 

evaluation process. The questions should target specific information presented on the display, its 

intended function, and whether it is usable for flight tasks required for typical instrument and 

commercial ratings. Besides using FAA pilots (including Designated Engineering Representative 

(DER) pilots), the applicant should consider conducting assessments with representative end 

user/operational pilots. Applicants should coordinate plans for any pilot evaluation with the 

responsible ACO.
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Appendix 9. Definitions and Acronyms

9-1. Definitions

a. Appliance (14 CFR 1.1) - Any instrument, mechanism, equipment, part, 

apparatus, appurtenance, or accessory, including communications equipment, that is used or 

intended to be used in operating or controlling an aircraft in flight, is installed in or attached to 

the aircraft, and is not part of an airframe, engine, or propeller.

b. Approach Lighting Designators

1. ALSF-I: High Intensity Approach Lighting System with Sequenced 

Flashing Lights, Category I Configuration.

2. ALSF-II: High Intensity Approach Lighting System with Sequenced 

Flashing Lights, Category II Configuration.

3. MALSR: Medium Intensity Approach Lighting System with Sequenced 

Flashing Lights.

4. SSALR: Simplified Short Approach Lighting System with Runway

Alignment Indicator Lights.

5. MALSF: Medium Intensity Approach Lighting System with Sequenced 

Flashing Lights.

6. RAIL: Runway Alignment Indicator Lights (RAIL).

7. SF: Sequenced Flashing Lights (SF).

c. Combined Vision System (CVS) - A system which combines information from 

an enhanced vision system and a synthetic vision system in a single integrated display.

d. Command Guidance - Symbolic information that directs the pilot to follow a 

course of action to control attitude or thrust in a specific situation (for example, flight director).

e. Conformal (AC 25-11A) - Refers to displayed graphic information that is aligned 

and scaled with the outside view.

f. Decision Altitude (14 CFR 1.1) - A specified altitude in an instrument approach 

procedure at which the pilot must decide whether to initiate an immediate missed approach if the 

pilot does not see the required visual reference, or to continue the approach. Decision altitude is 

expressed in feet above mean sea level.

g. Decision Height (14 CFR 1.1) - A specified height above the ground in an 

instrument approach procedure at which the pilot must decide whether to initiate an immediate 

missed approach if the pilot does not see the required visual reference, or to continue the 

approach. Decision height is expressed in feet above ground level.

h. Ego-centric - Used to define the view of a display image that correlates to inside 

the aircraft. One example is what the flight crew would see out the window from a forward 

facing perspective.

i. Enhanced Flight Visibility (EFV) (14 CFR 1.1) - The average forward 

horizontal distance, from the cockpit of an aircraft in flight, at which prominent topographical 
MM/DD/YYYY AC 20-167A

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objects can be clearly distinguished and identified by day or night by a pilot using an enhanced 

flight vision system.

j. Enhanced Flight Vision System (EFVS) (14 CFR 1.1) - An installed aircraft

system which uses an electronic means to provide a display of the forward external scene 

topography (the applicable natural or manmade features of a place or region especially in a way

to show their relative positions and elevation) through the use of imaging sensors, such as 

forward looking infrared, millimeter wave radiometry, millimeter wave radar, and/or low light 

level image intensifying. The EFVS sensor imagery and required aircraft flight information and 

flight symbology is displayed on a head-up display, or an equivalent display, on which the 

imagery and symbology is clearly visible to the pilot flying is his or her normal position with the 

line of vision looking forward along the flight path. An EFVS includes the display element, 

sensors, computers and power supplies, indications, and controls.

k. Enhanced Vision System (EVS) - An electronic means to provide a display of 

the forward external scene topography (the natural or manmade features of a place or region 

especially in a way to show their relative positions and elevation) through the use of imaging 

sensors, such as a forward looking infrared, millimeter wave radiometry, millimeter wave radar, 

low light level image intensifying.

Note 1: EASA uses term “EVS” as equivalent to FAA description of “EFVS.”

Note 2: Unlike an EFVS, an EVS does not necessarily provide the additional flight 

information/symbology required by 14 CFR 91.176, cannot use a head-up display or an 

equivalent display, and cannot be able to present the image and flight symbology in the same 

scale and alignment as the outside view. This system can provide situation awareness to the 

pilot, but does not meet the regulatory requirements of 14 CFR 91.176. As such, an EVS cannot 

be used as a means to determine enhanced flight visibility or to identify the required visual 

references and descend below the minimum descent altitude (MDA) or decision height (DH).

l. Equivalent Display - In the context of 14 CFR 91.176, a display which has at 

least the following characteristics:

1. A head-up presentation not requiring transition of visual attention from 

head down to head up.

2. Displays sensor-derived imagery conformal (as defined in SAE AS 8055) 

with the pilots external view.

3. Permits simultaneous view of the EFVS sensor imagery, required aircraft 

flight symbology, and the external view.

4. Display characteristics and dynamics are suitable for manual control of the 

aircraft.

m. Exocentric - Used to define the view of a display image that correlates to outside 

the aircraft. One common exocentric view would be a North Up Plan view shown on moving 

map displays.

n. Eye Reference Point (ERP) - The ERP is the point in the cockpit that allows for 

a finite reference enabling the precise determination of geometric entities that define the layout 

of the cockpit and displays.
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o. Field of Regard (FOR) (SAE ARP 5677) - The angular extent of the external 

world that is represented on a display.

p. Field of View (FOV) - The angular extent of the display that can be seen by

either pilot with the pilot seated at the pilot’s station. AC 25-11A provides the following 

diagram for primary field of view. See Figure 4 below.

Figure 4. Field of View

q. Flicker (RTCA/DO-315A) - High frequency luminance variations.

r. Flight Path Angle Reference Cue - Pilot selectable reference cue on the pitch 

scale displaying the desired approach angle.

s. Flight Path Vector - A symbol on the primary display (HUD or PFD) that shows 

where the aircraft is actually going, the sum of all forces acting on the aircraft.

t. Flight Visibility (14 CFR 1.1) - The average forward horizontal distance, from 

the cockpit of an aircraft in flight, at which prominent unlighted objects can be seen and 

identified by day and prominent lighted objects can be seen and identified by night.

u. Head Up Display (HUD) (AC 25.1329-1B) - A transparent optical display

system located level with and between the pilot and the forward windscreen. The HUD displays 

a combination of control, performance, navigation, and command information superimposed on 

the external field of view. It includes the display element, sensors, computers and power 

supplies, indications and controls. It is integrated with airborne attitude, air data and navigation 

systems, and as a display of command information is considered a component of the flight 

guidance system.

v. IFR conditions (14 CFR 1.1) - Weather conditions below the minimum for flight 

under visual flight rules.
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w. Instrument (14 CFR 1.1) - A device using an internal mechanism to show 

visually or aurally the attitude, altitude, or operation of an aircraft or aircraft part. It includes 

electronic devices for automatically controlling an aircraft in flight.

x. Jitter (RTCA/DO-315A) - High frequency positional oscillations.

y. Latency (AC 25-11A) - The time taken by the display system to react to a 

triggered event coming from an input/output device, the symbol generator, the graphic processor, 

or the information source.

z. Minimum Descent Altitude (14 CFR 1.1) - The lowest altitude, expressed in feet 

above mean sea level, to which descent is authorized on final approach or during circle-to-land 

maneuvering in execution of a standard instrument approach procedure, where no electronic 

glide slope is provided.

aa. Noise Equivalent Power (NEP) - Measure of the sensitivity of an optical 

detector or detector system.

bb. Noise Equivalent Temperature Difference (NETD) – A measure of the 

sensitivity of a detector of thermal radiation in the infrared, terahertz radiation, or microwave 

radiation parts of the electromagnetic spectrum.

cc. Non-Uniformity Correction (NUC) - Calibration of a detector utilizing more 

than one detector element.

dd. Precision Approach Procedure (14 CFR 1.1) - A standard instrument approach 

procedure in which a precision lateral and vertical path is provided.

ee. Primary Flight Display (PFD) - The displays used to present primary flight 

information.

ff. Rmax. - The maximum range the radar can detect.

gg. Situation Information (AC 120-29A, Criteria for Approval of Category I and 

Category II Weather Minima for Approach,) - Information that directly informs the pilot about 

the status of the aircraft system operations or specific flight parameters including flight path.

hh. Synthetic Vision (14 CFR 1.1) – A computer-generated image of the external 

scene topography from the perspective of the flight deck that is derived from aircraft attitude, 

high-precision navigation solution, and database of terrain, obstacles and relevant cultural 

features.

ii. Synthetic Vision System (SVS) (AC 25.1329-1) - An electronic means to display

a computer-generated image of the applicable external topography from the perspective of the 

flight deck that is derived from aircraft attitude, altitude, position, and a coordinate-referenced 

database.

Note: “Topography” defined as maps or charts of natural and man-made features of a 

place or region especially in a way to show their relative positions and elevations, as applicable 

whenever deemed appropriate and practicable.

jj. Thermal Crossover - The natural phenomenon that normally occurs twice daily

when temperature conditions are such that there is a loss of contrast between two adjacent 

objects on infrared imagery.
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kk. Threshold Crossing Height (TCH) (Pilot/Controller Glossary) - The theoretical 

height above the runway threshold at which the aircraft’s glideslope antenna would be if the 

aircraft maintains the trajectory established by the mean ILS glideslope.

ll. Visual References - Visual information the pilot derives from the observation of 

real-world cues, out the flight deck window, used as a primary reference for aircraft control or 

flight path assessment.

9-2. Acronyms.

AC Advisory circular

ACO Aircraft certification office

AFM Aircraft flight manual

BIT Built in test

CVS Combined vision system

DA Decision altitude

DEM Digital elevation model

DH Decision height

DTED Digital terrain elevation data

EASA European Aviation Safety Agency

EFB Electronic flight bag

EFIS Electronic flight instrument system

EFVS Enhanced flight vision system

EMI Electromagnetic interference

EVS Enhanced vision system

FAA Federal Aviation Administration

FHA Functional hazard analysis

FLIR Forward looking infrared

FMEA Failure mode and effects analysis

FOR Field of regard

FOV Field of view

FTA Fault tree analysis

HAT Height above touchdown

HDD Head-down display

HIRF High intensity radiated fields

HMI Hazardously misleading information

HTAWS Helicopter terrain awareness and warning system

HUD Head-up display

IFR Instrument flight rules

ILS Instrument landing system

MDA Minimum descent altitude

MDH Minimum descent height

MFD Multi-function display
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ND Navigation display

NETD Noise equivalent temperature difference

NUC Non-uniformity correction

PFD Primary flight display

PIO Pilot Induced Oscillation

RFM Rotorcraft flight manual

RVR

SSA

Runway Visual Range

System safety analysis

STC Sensitivity time control; supplemental type certificate

SVS Synthetic vision system

TAWS Terrain awareness and warning system

TC Type certificate

TCH Threshold crossing height

TDZE Touchdown zone elevation
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A10-1

Appendix 10. Related Publications

10-1. Related Publications.

a. FAA Documents:

1. Order 8110.4C, Type Certification.

2. Order 8110.54A, Instructions for Continued Airworthiness 

Responsibilities, Requirements, and Contents.

3. AC 23-18, Installation of Terrain Awareness and Warning System 

(TAWS) Approved for Part 23 Airplanes.

4. AC 23.1309-1E, Equipment, Systems, and Installations in Part 23 

Airplanes.

5. AC 23-1311-1C, Installation of Electronic Display Instrument Systems in 

Part 23 Airplanes.

6. AC 25-11A Electronic Flight Deck Displays.

7. AC 25-23, Airworthiness Criteria for the Installation Approval of a 

Terrain Awareness and Warning System (TAWS) for 14 CFR part 25 Airplanes.

8. AC 25.571-1D Damage Tolerance and Fatigue Evaluation of Structure

9. AC 25.629-1A Aeroelastic Stability Substantiation of Transport Category

Airplanes.

10. AC 25.1309-1A, System Design and Analysis.

11. AC 25.1329-1B, Approval of Flight Guidance Systems.

12. AC 25.1523-1, Minimum Flight Crew.

13. AC 27-1B, Certification of Normal Category Rotorcraft.

14. AC 29-2C, Certification of Transport Category Rotorcraft.

15. AC 90-106A Enhanced Flight Vision Systems

16. AC 91-16, Category II Operations General Aviation Airplanes.

17. AC 120-29A, Criteria for Approval of Category I and Category II Weather 

Minima for Approach.

18. AC 120-57A, Surface Movement Guidance and Control System.

19. AC 120-76B, Guidelines for the Certification, Airworthiness, and 

Operational Approval of Electronic Flight Bag Computing Devices.

20. FAA HUD, Certification Working Paper PS-ANM100-2001-0085.

b. RTCA, Inc. Documents
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1. DO-160F, Environmental Conditions and Test Procedures for Airborne 

Equipment.

2. DO-178B, Software Considerations in Airborne Systems and Equipment 

Certification.

3. DO-200A, Standards for Processing Aeronautical Data.

4. DO-254, Design Assurance Guidance for Airborne Electronic Hardware.

5. DO-276A, User Requirements for Terrain and Obstacle Data.

6. DO-309, Minimum Operational Performance Standards (MOPS) for 

Helicopter Terrain Awareness and Warning System (HTAWS) Airborne Equipment.

7. DO-315A, Minimum Aviation System Performance Standards (MASPS) 

for Enhanced Vision Systems, Synthetic Vision Systems, Combined Vision Systems, and 

Enhanced Flight Vision Systems.

c. SAE International Documents.

1. ARP 4101, Flight Deck Layout and Facilities.

2. ARP 4102, Flight Deck Panels, Controls and Displays.

3. ARP 4103, Flight Deck Lighting and Visual Interface.

4. ARP 4105, Nomenclature and Abbreviations for Use on the Flight Deck.

5. ARP 4754, Certification Considerations for Highly-Integrated Or 

Complex Aircraft Systems.

6. ARP 4761, Guidelines and Methods for Conducting the Safety 

Assessment Process on Civil Airborne Systems and Equipment

7. ARP 5288, Transport Category Airplane Head Up Display (HUD) 

Systems.

8. ARP 5589, Human Engineering Considerations for Design and 

Implementation of Perspective Flight Guidance Displays.

9. ARP 5677, Human Engineering Considerations for Cockpit Integration of 

Enhanced/Synthetic Vision Systems.

10. AS 5703, Minimum Performance Standard for Enhanced Vision System.

11. AS 8055, Minimum Performance Standard for Airborne Head Up Display

(HUD).

10-2. How to Get Publications.

a. Order copies of 14 CFR, from the Superintendent of Documents, Government 

Printing Office, P.O. 979050, St. Louis, MO 63197. For general information, telephone (202) 

512-1800 or fax (202) 512-2250. You can order copies online at www.access.gpo.gov. Select 

“Access” then “Online Bookstore.” Select “Aviation,” then “Code of Federal Regulations.”

b. You can get copies of FAA ACs from the FAA website at www.airweb.faa.gov or 

www.faa.gov/reugulations_policies/advisory_circulars/.
MM/DD/YYYY AC 20-167A

A10-3

c. You can find a current list of TSOs on the FAA Internet website Regulatory and 

Guidance Library at www.airweb.faa.gov/rgl. You will also find the TSO Index of Articles at 

the same site.

d. Order copies of RTCA documents from RTCA, Inc., 1150 18th St., NW, Suite 

910, Washington, DC 20036, telephone (202) 833-9339, fax (202) 833-9434, or website: 

www.rtca.org

e. Order copies of SAE documents from SAE World Headquarters, 400 

Commonwealth Drive, Warrendale, PA 15096-0001, USA, telephone: (877) 606-7323, or 

website: http://www.sae.org.

f. Order copies of military documents from the Department of Defense Index of 

Specifications and Standards (DODSSP), Building 4/Section D, 700 Robbins Avenue, 

Philadelphia, PA 19111-5098. Telephone (215) 697-2179, fax (215) 697-1462. You can also 

order copies online at http://dodssp.daps.dla.mil