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.
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 should include the 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.
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 the length of transmission over a path with generalised extinction coefficients at a given wavelength.
EUROCAE ED-291 Test Procedures for Quantified Visual Advantage Issue 1 contains an acceptable methodology for determining and quantifying the visual advantage for an EFVS-A or EFVS-L, and should be used as the basis for the flight test.
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 helpful in assessing performance and viability for the required functions.
Both the installed system and the individual system components should be verified to ensure compliance with the requirements in Book 1 Subpart A Section 3.
Airframe and equipment manufacturer-based tests or analyses, as applicable, should be developed and conducted to validate the detailed system criteria. No specific test procedures are cited because alternative methods can be used. Alternate procedures can be utilised if it can be demonstrated that they provide the totality of the required information. System performance tests are the most important tests as they relate to operational capability. Subsystem tests are used as subsystems are added during system build-up to ensure appropriate subsystem performance as it relates to overall system performance.
An evaluation of the system used during anticipated operational scenarios should be conducted.
The minimum detection EFVS range can be derived by using an assumed minimum distance of the aircraft at the nominal Category I (200 ft) DA before which the EFVS should image the visual cues required by AMC7 SPA.LVO.105(c) point (e).
Sensor resolution
As a minimum, the EFVS resolution performance shall adequately resolve (for pilot identification) the runway threshold and the TDZ to enable the intended function. For example, an EFVS should resolve a 60-ft wide runway from 200 ft height above the TDZE with a typical 3-degree glideslope. The sensor resolution has been 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 NPAs which may require greater distances.) A 60-ft wide runway has been chosen as the ICAO minimum runway width to support instrument approach procedures.
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 the TDZE with a typical 3-degree glideslope. The pilot needs to be able to detect and accurately identify the visual references in the image.
Performance demonstration
The performance demonstration, establishing aircraft system compliance, 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, missed approaches, failure conditions, crosswind conditions, and approaches into specific aerodromes as appropriate for the system's intended function. For EFVSs, performance at the lateral and vertical limits for the type of approach (for example, precision, non-precision, and approach with vertical guidance) for which operational credit is being sought should be demonstrated.
The applicant should demonstrate compliance through flight test using an aircraft that is fully representative for the purpose of the test in terms of flight deck geometry, instrumentation, alerts, indications, and controls (in the air or on the ground).
In addition, the applicant should use any of these three general verification methods to supplement flight testing:
- (a) Analysis: demonstrate compliance using an engineering analysis. - (b) Laboratory test: demonstrate compliance using an engineering bench representative of the final EFVS being certified. - (c) Simulation: demonstrate compliance using a flight simulator.
The individual verification methods that are to be used should be specified in the certification plan to be agreed by EASA. For extensions, features, and design decisions not explicitly specified in this certification specification, human factors evaluations should be conducted through analyses, bench, simulation, or flight testing.
Final approach course offsets greater than 3 degrees should be subject to additional flight test evaluation. The maximum allowable final approach course offset is established by flight testing. This testing should include the factors related to the offset, such as HUD/EFVS FOV, crosswinds, and the maximum drift angle for a conformal FPV.
Benchmark data establishing equivalence to normal visual operations with a specific aircraft should not normally be necessary. However, if flight test results show deviations from the standard criteria listed above, then benchmark data might be used to establish the equivalence of operations with EFVS-L to normal visual operations for that specific aircraft.
The image/symbology of EFVS-L should provide the visual cues for the pilot to perform the following actions without requiring exceptional piloting skill, alerting, strength, or excessive workload:
- (a) Speed control within +10/ -5 kt of the approach speed, whether manually controlled or with auto-throttle, up to the point where the throttles are retarded for landing. - (b) A smooth transition through flare to landing. - (c) Approach, flare, and landing at a normal sink rate for the aircraft. - (d) All touchdowns in the TDZ. Lateral touchdown performance should be demonstrated to be no worse than that achieved in visual operations with natural vision for a specific aircraft. Longitudinal touchdown performance must be demonstrated within the TDZ which is the first one third, or the first 3 000 ft, of the usable runway, whichever is more restrictive, and demonstrated to be equivalent to or better than that achieved in visual operations with natural vision for that specific aircraft. - (e) Prompt and predictable correction of any lateral deviation away from the runway centre line to smoothly intercept the centre line. - (f) Touchdowns with a bank angle that is not hazardous to the aeroplane. - (g) Demonstrated performance of the installed EFVS at representative visibilities for operations conducted with EFVS-A and EFVS-L, as described in this document, will determine any additional limitation (for example, crosswind and offset). - (h) A normal derotation.
- (i) Satisfactory and smooth control of the aeroplane from touchdown to a safe taxi speed. - (j) Satisfactory and smooth control of the path of the aeroplane along the runway centre line through roll-out to a safe taxi speed. - (k) A safe go-around at any time, including up to touchdown in all configurations to be certified.
EFVS-L performance demonstration
For EFVS-Ls and, 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 use of a visibility-limiting device for system performance demonstrations is selected. Visibility-limiting devices may not adequately simulate low-visibility conditions for all performance demonstrations of EFVS-Ls because of the unrealistically good external visibility outside the HUD FOV and the unrealistic image performance of the EFVS-Ls in good atmospheric conditions.
[Issue: CS-AWO/2]