AWO.A.EFVS.104 CS AWO.A.EFVS.104 Enhanced flight vision system display

The EFVS imagery should not degrade the 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, should not be hindered or compromised by the EFVS image on the HUD.

The EFVS imagery displayed on the HUD or equivalent display must account for the pilot compartment view requirements found in CS 25.773 or CS 23.2600, including validation that the display of imagery does not conflict with the pilot compartment view. The display of the EFVS sensor imagery should be on a system that compensates for the interference caused by the provided imagery. Additionally, the system should provide an undistorted and conformal view of the external scene, a means to deactivate the display, and should not restrict the pilot from performing specific manoeuvres. The following tasks associated with the use of the pilot's view should not be degraded below the level of sa fety that existed without the video imagery:

- (a) Detection, accurate identification and manoeuvring, as necessary, to avoid traffic, terrain, obstacles, and other hazards of flight. - (b) Accurate identification and utilisation of visual references required for every task relevant to the respective 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 distraction to the pilots due to sensor proximity to the taxiway surface .

For EFVSs that are implemented on a HUD, the image should be compatible with the FOV and head motion box of a HUD designed against SAE ARP5288 Transport Category Airplane Head Up Display (HUD) Systems. When used in a given phase of flight, the HUD and the EFVS FOR must provide a conformal image with the visual scene over the range of aircraft attitudes and wind conditions.

EFVS display criteria must meet the CS-23 or CS-25 airworthiness specifications (as applicable) (see Appendix 1 to the AMC to Section 3 of Subpart A). Some of these specifications could be specific to EFVSs and could be in addition to all other requirements applicable to the HUD and the basic avionics installation. The amount of new test data can be determined by the individual application, availability, and relevance of data.

Easy Access Rules for All-Weather Operations (CS-AWO)

The current certification specifications for HUDs apply with respect to EFVSs. These criteria include well-established military as well as civil aviation standards for HUDs as defined in MIL-STD-1787C Aircraft Display Symbology and in AMC 25-11. SAE design standards for HUD symbology, optical elements, and video imagery are also prescribed within SAE AS8055 Minimum Performance Standard for Airborne Head Up Display (HUD), SAE ARP5288 Transport Category Airplane Head Up Display (HUD) Systems, and SAE ARP5287 Optical Measurement Procedures for Airborne Head Up Display (HUD). The specific design standards for image size, resolution and line width, luminance and contrast ratio, chromaticity, and grayscale should be applied.

A HUD modified to display EFVS imagery should 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, quick-glance interpretation of attitude should be possible for all unusual attitude situations and other 'non -normal' manoeuvres to permit the pilot to recognise the unusual atti tude and initiate recovery within 1 second. The use of chevrons, pointers, and/or permanent ground-sky horizon on all attitude indications to perform effective manual recovery from unusual attitudes is recommended. Refer to AMC 25-11 for guidance on electronic flight deck displays.

EFVS latency should be no greater than 100 milliseconds (ms). Latency should not be discernible to the pilot and should not affect control performance nor 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 manoeuvres in the absence of other visual cues.

EFVS field of regard (FOR)

The minimum fixed FOR should be 20 degrees horizontally and 15 degrees vertically. In applications where the FOR is centred on the flight path vector (FPV), the minimum vertical FOR should be 5 degrees (± 2.5 degrees) and 20 degrees horizontally.

- (a) The minimum EFVS FOR should not only consider the HUD FOV (i.e. the size of the area that is 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 aspects: - (1) HUD and EFVS sensor FOV; - (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, if FOR is centred on FPV. - (b) SAE ARP5288 Transport Category Airplane Head Up Display (HUD) Systems 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 should be established as a minimum design criterion to be qualitatively checked during the certification flight test for sufficiency in meeting its intended function. The EFVS FOR should result from consideration of the minimum FOR criteria for various aircraft attitudes and wind conditions using a critical altitude of 200 ft height above TDZE for EFVS visibility.

- (c) A variable FOR is permissible assuming a slewable sensor (i.e. variable FOR), centred on the FPV, with a minimum ±2.5 degrees about the FPV to allow for momentary flight path perturbations and to allow for sufficient fore/aft view of the required visual references.

Off-axis rejection

A source in object space that is greater than 1 degree outside the FOV should not result in any perceptible point or edge-like image within the FOV. The EFVS should preclude off-axis information from folding into the primary FOR imagery, creating the potential for misleading or distracting imagery.

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 ARP5288. This implies that the EFVS and the HUD cannot exhibit jitter greater than that of the HUD itself.

Flicker

Flicker is brightness variations at frequency above 0.25 Hz as per SAE ARP5288. The minimum standard for flicker should meet the criteria of SAE ARP5288. Flicker can cause mild fatigue and reduced crew efficiency. Therefore, the EFVS and the HUD should not exhibit flicker greater than that of the HUD itself.

Image artefacts

The EFVS should not exhibit any objectionable noise, local disturbances, or an artefact that prevents the system from meeting its intended function. The EFVS design should minimise display characteristics or artefacts (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.

Image conformality

The accuracy of the integrated EFVS and HUD image should not result in a greater than 5 mrad display error at the centre of the display at a range of 2 000 ft (100 ft altitude on a 3-degree glideslope). In accordance with SAE ARP5288, 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 ARP5288. 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 that 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 TDZE, the EFVS conformality error introduces error in the pilot's ability to track along the extended centre line / vertical glid e path as the pilot flies the FPV and glide path reference line toward the EFVS image of the runway.

Dynamic range

The minimum required dynamic range for passive EFVSs should be 48 dB. For active EFVSs, side lobes should be 23 dB below the main beam, and 40 dB dynamic range plus sensitivity time control.

Sensor image calibration

Visible image calibrations and other built-in tests that cannot be achieved within a total latency of 100 ms should occur only either on 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 should be removed from the pilot's display. This prohibits excessive times to compl ete 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 the effect based on training and experience). Abnormal imagery should be removed from the display to eliminate the potential for any misleading information.

Passive sensor optical distortion

Optical distortion should be 5 % or less across the minimal FOR and no greater than 8 % outside the minimal FOR.

Sensor sensitivity

In this context, the EFVS sensor sensitivity should be at least a noise-equivalent temperature difference (NETD) of 50° mK tested at an appropriate ambient temperature for passive EFVSs or -20 dB sm/sm (square metre/square metre) surface at Rmax from 200 ft height above TDZE with a typical 3° glideslope for active EFVSs. Passive sensors for different visible or short-wave infrared sources can require very sensitive detectors, as specified by low noise-equivalent powers.

Blooming

The sensor should incorporate features to minimise blooming, which can create an unusable or objectionable image. Objectionable blooming is defined as the condition that obscures the required visual cues. Blooming to the extent the required visual references are no longer distinctly visible and identifiable is unacceptable.

Image persistence

The image persistence time constant should be less than 100 ms. 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. Image artefacts should be removed by a secondary on-demand process (for example, the non-uniformity correction (NUC) process).

Dead pixels

Dead pixels or sensor elements replaced by a 'bad pixel' replacement algorithm shou ld be limited to 1 % average of the total display area, with no cluster greater than 0.02 % 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.

Parallax

The effects of parallax caused by lateral, vertical, and longitudinal offset of the sensor from the pilots' design eye points should not impede the E FVS from performing its intended function, as evaluated during flight test. Parallax should not cause unsatisfactory landing performance parameters (e.g. flare height, sink rate, touchdown location, ground speed during landing, exit and taxiing) between EFVS operations and visual operations in the same aircraft.

[Issue: CS-AWO/2]