4-14 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 performance value. 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.
Figure 3. Minimum Detection Range
4.5.1.10 The EFVS imagery displayed on the HUD or equivalent display 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 must be on a system that compensates for the interference caused by the provided imagery. Additionally, the system must provide an undistorted and conformal view of the external scene, 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:
Detection, accurate identification and maneuvering, as necessary, to avoid traffic, terrain, obstacles, and other hazards of flight.
Accurate identification and utilization of visual references required for every task relevant to the phase of flight.
Note: Although, the EFVS image requirements relate primarily to the approach and landing phases of flight, the EFVS image when viewed head up during ground operations should not create unacceptable distractions due to sensor proximity to the taxiway surface.
4.5.2 EFVS General System Criteria.
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4.5.2.1 For EFVS implemented on a HUD, the 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). When used in a given phase of flight, the HUD and EFVS FOR must provide a conformal image with the visual scene over the range of aircraft attitudes and wind conditions. A display that provides the pilot monitoring with EFVS sensor imagery is not required for EFVS Approach System operations. However, for EFVS Landing System 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. Any display used to monitor the approach must be located in the cockpit in accordance with 14 CFR §§ 23/25/27/29.1321 so that any pilot seated at the controls can monitor the airplane’s flight path and instruments with minimum head and eye movement. Aircraft that pre-date 14 CFR §§ 23/25/27/29.1321 must meet the arrangement and visibility requirements in those sections for the installation of pilot monitoring displays. Any symbology displayed must not adversely obscure the sensor imagery of the runway environment.
4.5.2.2 EFVS display criteria must meet the airworthiness certification requirements in 14 CFR parts 21, 23, 25, 27, and 29 (as applicable), see Appendix A. Some of these requirements could be specific to EFVS and could be in addition to all other requirements applicable to the HUD and the basic avionics installation.
4.5.2.3 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 25-11B. 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.
4.5.2.4 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:
4.5.2.4.1 Be suitable for and successfully perform its intended function.
4.5.2.4.2 Allow the accurate identification and utilization of visual references, using both EFVS and natural vision as appropriate.
4.5.2.4.3 Have acceptable display characteristics to accomplish the intended function.
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4.5.2.4.4 There must be a means to allow 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 and power controls, or their equivalent. (Ref 14 CFR §§ 23.773(c)(3), 25.775(e)(3), 27.773(c)(3), and 29.773(c)(3)).
4.5.2.4.5 Not degrade the presentation of essential flight information on the HUD or equivalent display.
4.5.2.4.6 Not be misleading and should not cause confusion or any significant increase in pilot workload.
4.5.2.4.7 Be aligned with and scaled to the external scene, and should include the effect of near distance parallax.
4.5.2.4.8 Not cause unacceptable interference with the safe and effective use of the pilot compartment view.
4.5.2.4.9 Not misleadingly alter the color perception of the external scene so as to preclude the pilot’s performance of any required tasks by causing confusion or any significant increase in its workload, e.g. discerning PAPI lights accurately on approach.
4.5.2.4.10 Allow the pilot to recognize significantly misaligned or non-conformal conditions to the external scene that may preclude the pilot’s performance of any required maneuvers.
4.5.2.5 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.
4.5.2.6 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 the EFVS is used. An accurate, easy, quickglance 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 25-11B for guidance on electronic flight deck displays.
4.5.2.7 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:
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4.5.2.7.1 The position and motion of the FPV should correspond to the aircraft’s earth referenced flight path vector.
4.5.2.7.2 The dynamic response of FPV should follow pilot control inputs. Refer to SAE ARP 5589 for dynamic response guidance.
4.5.2.7.3 The display of the FPARC should be suitable for monitoring the vertical flight path of the aircraft.
4.5.2.7.4 The system must provide the pilot a means to select the desired descent angle that is represented by the FPARC, and may also provide a means for the descent angle to be selected automatically from a database.
4.5.2.8 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.
4.5.2.9 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.
4.5.3 EFVS Detailed System Criteria.
4.5.3.1 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.
4.5.3.2 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.
4.5.3.3 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 relevant frequencies. The analysis should portray 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 attenuation
4-18 helpful in assessing performance and viability for the functions required under 14 CFR § 91.176.
4.5.3.4 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.
4.5.3.4.1 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 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.
4.5.3.4.2 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.
4.5.3.4.2.1 The 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:
HUD and EFVS sensor Field-Of-View;
Orientation of the HUD with respect to the aircraft frame of reference (for example, boresight and proximity to pilot’s eye); and Orientation (for example, attitude) of the aircraft.
4.5.3.4.2.2 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 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
4-19 for various aircraft attitudes and wind conditions using a critical altitude of 200 ft height above touchdown zone elevation for EFVS visibility.
4.5.3.4.2.3 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.
4.5.3.4.3 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 view. The EFVS should preclude off-axis information from folding into the primary FOR imagery, creating the potential for misleading or distracting imagery.
4.5.3.4.4 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.
4.5.3.4.5 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. The EFVS and HUD cannot exhibit flicker greater than that of the HUD itself.
4.5.3.4.6 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 should 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.
4.5.3.4.7 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
4-20 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.
4.5.3.4.8 Sensor/sensor processor.
4.5.3.4.8.1 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).
4.5.3.4.8.2 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 non-critical 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 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).
Abnormal imagery should be removed from the display to eliminate the potential for any misleading information.
4.5.3.4.8.3 Sensor resolution. As a minimum, EFVS resolution performance shall adequately resolve (for pilot identification) the runway threshold and the touchdown zone to enable the intended function. For example, an EFVS should resolve a 60 ft wide runway from 200 ft height above touchdown zone elevation with a typical 3- degree glide slope. The 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 nonprecision 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.
4.5.3.4.8.4 Passive sensor optical distortion. Optical distortion should be 5 percent or less across the minimal FOR as defined in
4-21 paragraph 4.5.3.4.2 and no greater than 8 percent outside the minimal FOR.
4.5.3.4.8.5 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.
4.5.3.4.8.6 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.
4.5.3.4.8.7 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.
4.5.3.4.8.8 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 4.5.3.4.6, Image artifacts, by a secondary on-demand process (for example, the NUC process).
4.5.3.4.8.9 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 closely-spaced location of the element.
4.5.3.4.8.10 Parallax. The effects of parallax caused by lateral, vertical, and longitudinal offset of the sensor from the pilots’ design eye points may not impede the EFVS from performing its
4-22 intended function, as evaluated during flight test. Parallax should not cause unsatisfactory landing 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.
5-1 CHAPTER 5. SYSTEMS INSTALLATION CONSIDERATIONS
5.1 EVS/SVS/CVS Installations Considerations
5.1.1 EVS/SVS/CVS Pilot Controls.
5.1.1.1 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.
5.1.1.2 The EVS/SVS/CVS controls, except those located on the pilot’s control inceptor (e.g., control wheel, yoke, stick, etc.), must be adequately illuminated for all normal background lighting conditions and must not create any objectionable reflections on other flight instruments.
5.1.1.3 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.
5.1.2 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 8110.54A), or other methods, techniques, and practices acceptable to the Administrator.
5.1.3 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.
5.1.4 The electrical system must be able to furnish the required power at the proper voltage for the EVS/SVS/CVS.
5.1.5 EVS/SVS/CVS System Safety Design Criteria. The overall safety requirement of the aircraft is based on installed equipment. A complete functional hazard assessment (FHA) and system safety analysis (SSA) should be conducted to identify failure modes and classify the hazard levels. To meet the safety criteria in 14 CFR §§ 23/25/27/29.1309, 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.
5.1.6 EVS/SVS/CVS Required Safety Level.
5.1.6.1.1 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
5-2 Effects Analysis (FMEA). A system safety assessment should be performed in accordance with 14 CFR §§ 23/25/27/29.1309 that addresses both the loss as well as the incorrect display of information, including hazardously misleading information. Undetected failure conditions which cause a hazardously misleading EFVS depiction must have a probability no greater than that appropriate for the hazard effects they create.
5.1.6.1.2 To support the 14 CFR §§ 23/25/27/29.1309 analysis (as applicable), the applicant must perform a safety assessment 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 ramifications of a “frozen EVS/SVS/CVS display” that is undetected by the flight crew.
5.1.6.1.3 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.
5.1.6.1.4 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 should 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
5-3
5.1.6.1.5 The normal operation (without malfunction) of the EVS/SVS/CVS may not adversely affect, or be adversely affected by other normally operating aircraft functions. 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 §§ 23/25/27/29.1309, AC 25-11B chapter 4, and AC 23/25/27/29.1309, 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 §§ 23/25/27/29.1309, AC 25-11B chapter 4, and AC 23/25/27/29.1309. As applicable, similar criteria are found in SAE ARP 4754, and ARP 4761.
5.1.7 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-160F (or as revised) Environmental Conditions and Test Procedures for Airborne Equipment. These criteria must also include the high-intensity radiated fields (HIRF), 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 be designed in a manner that lightning strikes on the EVS/SVS/CVS system does not cause catastrophic effects on the aircraft.
5.2 EFVS Display (HUD or Equivalent) Installation Considerations
5.2.1 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.
5.2.2 EFVS Display.
5.2.2.1 Display resolution. 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.
5.2.2.2 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.