AC 27-1B, Chg 1 2/12/03 (B) The aviation Authority should coordinate with engineering in evaluating the revised MEL.
VOTE: Any MMEL allowance should be determined considering the criticality of the credit effect resulting trom the HUMS application (s). MMEL allowances should be substantiated based on a Functional Hazard Assessment (FHA).
Page MG 15 - 18
CHAPTER 3
AIRWORTHINESS STANDARDS
NORMAL CATEGORY ROTORCRAFT
MISCELLANEOUS GUIDANCE (MG) AC 27 MG 16. CERTIFICATION GUIDANCE FOR ROTORCRAFT NIGHT VISION IMAGING SYSTEM (NVIS) AIRCRAFT LIGHTING SYSTEMS.
a. Purpose. The guidance in this MG is one method to show compliance with 14 CFR part 27 regarding aircraft lighting modification for NVIS compatibility Additional guidance is found in RTCA Document DO-275, Minimum Operational Performance Standards for Integrated Night Vision Imaging System Equipment, issued October 12, 2001. The applicant should also be familiar with RTCA Document DO-268, Concept of Operations: Night Vision Imaging System for Civil Operators, issued March 27, 2001. For operations within Europe, applicants should also be familiar with Joint Aviation Authorities Temporary Guidance Leaflet No. 34, Night Vision Imaging System (NVIS) Operations. For NVIS operations outside the United States, other similar documents may also apply.
b. Revisions.
(1) This revision focuses the guidance on NVIS lighting and night vision goggles (NVG) and NVIS lighting cockpit compatibility
(2) NVIS and NVG cockpit evaluation guides and checklists are located at http://www.faa.gov/aircraft/air_cert/design_approvals/rotorcraft/nvis/.
c. Definitions.
(1) Cultural lighting. Light emitted from cities, towns, residences, streetlights, or other artificial sources. Cultural lighting may help or hinder the pilot's external view through NGs depending on intensity, reflection off cloud cover, landing zone, and topography.
(2) Night vision imaging system (NVIS). A system that integrates all elements (including the NVG, windshield, and lighting system) required to operate an aircraft successfully and safely with the aid of NVGs.
(3) NVIS lighting component. Any component intended for use with NVGs that emits or transmits light within the flight deck or other crew compartments, or attached to the aircraft exterior, and does not degrade NVG performance.
(4) NVIS lighting system. An aircraft lighting system modified or designed to incorporate NVIS lighting components. It provides adequate illumination, under day and night conditions, of instruments, displays, and controls for the unaided eye without degrading NVG performance. NVIS lighting systems must meet part 27 lighting requirements.
(5) NVIS-friendly (as applicable to external lights). NVIS-friendly exterior lights can be viewed by the unaided eye, meet the position light requirements of §27.1385, and do not significantly interfere with NVG performance. An NVIS-friendly exterior light emits more NVG-detectable (usually infrared (IR)), wavelengths of energy as compared to lights that are completely NVIS-compatible. An NVIS-friendly exterior light will be detected when viewed through the NGs and not overwhelm the aircraft outline or cause shadowing or objectionable reflections off the aircraft. When viewed through NVGs, the light does not cause excessive "blooming," where lights merge together and obscure the outline of the aircraft.
(6) NG-compatible. Aircraft internal and external lighting is NVG-compatible when it does not adversely affect the NVG image.
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(7) Aided flight. A flight in which the flight crew references NVG imagery to assist visual flight.
(8) Unaided flight. A flight in which the flight crew does not reference NVG imagery.
(9) Transparencies. Windshields, windows, chin bubbles, and overhead windows through which the crew views the outside scene with NVGs.
(10) Inadvertent instrument meteorological conditions (IMC). An unplanned encounter with visual conditions that do not permit continued flight under VFR where conditions do not allow for the visual determination of a usable horizon (e.g., fog, snow showers, or night operations over unlit surfaces such as water). Some examples where inadvertent IMC may occur are flight into areas with no lights or other features that allow for visual contact with the ground or horizon; actual IMC-like entering clouds; brownout or white out during approaches or takeoffs from dusty or snow covered unimproved landing zones; or whiteout because of blowing and falling snow.
(11) Unimproved landing area. Any site that is not an airport, heliport, or other civil aviation authority approved landing site.
d. References (use the current versions of the following references).
(1) Regulatory (14 CFR sections).
27.1 27.1322 27.1501
27.21 27.1351 27.1523
27.141(c) 27.1357 27.1525
27.603(c) 27.1367 27.1529
27.771 27.1381 27.1541
27.773 27.1383 27.1543
27.777 27.1385 27.1545
27.785 27.1387 27.1549
27.807(b)(3) 27.1389 27.1553
27.853 27.1391 27.1555
27.1301 27.1393 27.1557
27.1303 27.1395 27.1561
27.1305 27.1397 27.1581
27.1307 27.1399 27.1583
27.1309 27.1401 27.1585
27.1321
(2) Other reference.
Document Title AC 25-11 Electronic Flight Displays AC 20-74 Aircraft Position and Anticollision Light Measurements AC 20-88 Guidelines on the Marking of Aircraft Powerplant Instruments (Displays) AC 20-152 RTCA, Inc., Document RTCA/DO-254, Design Assurance Guidance for Airborne Electronic Hardware RTCA DO-268 Concept of Operations, Night Vision Imaging System for Civil Operators RTCA DO-275 Minimum Operational Performance Standards for Integrated Night Vision Imaging System Equipment SAE ARP 4754 Guidelines for Development of Civil Aircraft and Systems SAE ARP 4761 Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment Page MG 16-2
Document Title SAE ARP 5825 Design Requirements and Test Procedures for Dual Mode Exterior Lights TSO-C4c Bank and Pitch Instruments TSO-C8e Vertical Velocity Instruments (Rate-of-Climb) TSO-C87 Airborne Low-Range Radio Altimeter TSO-C164 Night Vision Goggles
e. Background.
(1) The guiding technical specifications document for NVIS lighting is RTCA/DO-275, Minimum Operational Performance Standards for Integrated Night Vision Imaging System Equipment, in addition to the means of compliance presented in this advisory circular. The lighting system should be designed to be used with NVGs that meet the performance requirements of FAA TSO-C164 Night Vision Goggles.
(2) We harmonized this guidance with the European Aviation Safety Agency (EASA) and Transport Canada Civil Aviation (TCCA) NVIS lighting guidance documents.
(3) Certification of NGs is not included in this guidance.
(4) The primary tenet of the use of NVGs in civil flight operations is that they are an aid to VFR flight. NGs are not intended to expand an aircraft's operational envelope or expand operational capabilities.
(5) NVGs used to evaluate NVIS lighting systems will be the same make-model part number used by the operator whose aircraft is being modified, and the NVGs should meet the performance requirements of TSO-C164 and RTCA Document DO-275.
(6) This guidance is for use with NVIS using NGs and does not apply to other night or low visual environment enhancement devices (forward-looking infrared system (FLIR), enhanced vision system (EVS), etc.).
(7) NGs enhance a pilot's night vision by amplifying certain energy frequencies. The NGs for civil use are based on performance criteria in TSO-C164 and RTCA Document DO-275.. These NGS are known as "Class B NVG" because they have a filter applied to the objective lens that blocks energy below the wavelength of 665 nanometers (nm). The Class B objective lens filter allows more use of color in the cockpit with truer reds and ambers. The TSO specifies Class B NVGs for civil use. Because NVGS will amplify energy that is not within the range of the filter, it is important that the NVIS lighting system keep those incompatible frequencies out of the cockpit. However, there are NVGs in civil use that do not conform to the TSO-C164 standard because they have Class A filters on their objective lenses. Class A filters block energy below the wavelength of 625 nm. As a result, Class A NGs will amplify more wavelengths of visible light requiring special care in the use of color in the cockpit. Applicants and operators are advised to review RTCA Document DO-275 to familiarize themselves with Classes of
(8) Modifications that make an aircraft NVIS-compliant are a major alteration or change, due to the fundamental effect visible and near-IR wavelength energy has on NVGs that, in turn, directly affects the pilot's visual perception.
(9) Any changes to a certificated NVIS lighting system are major changes under § 21.93(a) since they may affect the operational characteristics of the aircraft). Consequently, evaluate any changes in accordance with this guidance.
(10) There are two processes involved in the certification of aircraft NVIS lighting:
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(i) Installation and certification of the NVIS-compatible lighting on the aircraft. This process ensures the NVIS lighting installation is compatible with day and night-unaided (without NVG) use.
(ii) Certification that the installed NVIS lighting is compatible with NVG operations. The structure of this guidance is to assist in both the design and installation of the NVIS lighting system and in the certification that the lighting system is NVG compatible. Compatibility of the NVIS installation and NGs must be assessed using each make and model part number of the NVG that the applicant proposes for NVIS operations. Any subsequent change in the goggle specification or cockpit lighting configuration may render the current approval invalid and will require a re-evaluation for NVIS cockpit and NVG compatibility.
Notes: Aircraft intended for NVG operations must go through the NVIS certification process, whether modified by supplemental type certificate (STC) or produced by the aircraft manufacturer.
Basic aircraft approval for day and night VFR does not constitute NVIS certification. In addition, some rotorcraft may not be suitable for NVIS certification due to factors such as cockpit obstructions, inability of pilots to move their heads while wearing NVGs, inability of the cockpit to accommodate a pilot wearing a helmet, etc.
Certification ground and flight test scheduling should account for nighttime ambient lighting conditions. Type inspection authorization (TIA) flights should be accomplished in no-moon conditions to avoid masking possible low illumination, incompatible lighting effects during the NVIS cockpit, and NVG interface evaluations. In addition, fly the flight test in areas where there is little or no cultural lighting.
Installation of a NVIS lighting system does not authorize the operation of NVGs. The operator must coordinate with the FAA oversight office to obtain operational authorization.
Page MG 16-4
†. Procedures
(1) General. One method to show compliance is outlined in this AC and includes evaluation of the NVIS lighting system and cockpit through both day, night ground, night aided, and night unaided flight evaluations.
(2) Certification basis. The NVIS lighting design, not including the NVG, must comply with the same certification basis as that of the aircraft. The NVIS lighting design should not adversely affect other design approvals (e.g., category A and IFR).
Category A profiles are not normally flown during NVG/NVIS lighting compatibility evaluations.
Therefore, the aircraft's capability to support category A profiles during NVG operations is not known. As a result, use of NVGs during performance of category A profiles should be evaluated prior to authorizing their use The capability of the aircraft to support NVG use with flight operations that require special training and approval (such as agricultural and external load operations) is beyond the scope of this MG.
(3) Additional NVIS equipment and components. Due to the limitations of NVGs, the installation of additional instruments, equipment, or controls may be necessary for a successful NVIS certification.
Examples include attitude indicator(s), vertical speed indicator(s), radar (radio) altimeters), and two-way radio communication equipment. The applicable operating rules and RTCA Document DO-268 provide additional detail on minimum equipment requirements.
(4) Installation design.
(i) TSO approval does not ensure instruments will be acceptable in a particular cockpit installation or for all lighting conditions.
(ii) Basic aircraft lighting may have characteristics that may require changes to support certain types of NVIS lighting modifications. Depending on the type of NVIS lighting modification, any uncorrected problems in the basic aircraft lighting system may be exacerbated and lead to the modification being unacceptable. Prior to designing or installing a NVIS lighting system, ensure the basic aircraft is suitable for NG operations as follows:
(A) The basic aircraft lighting system will support the planned type of NVIS modification.
(B) All gauges are illuminated and lighting levels can balance across the cockpit.
(C) All flight instruments are legible at night with night lighting settings and balance with other instruments and gauges in the instrument panel.
(D) All lighted switches and panels illuminated by the basic aircraft lighting system are readable and light levels balanced with the rest of the cockpit.
(E) The basic, unmodified crew alerting system and caution warning panel is readable in both daylight (with sunlight on the display) and night lighting conditions.
(F) Annunciators and other push button switches with illuminated legends are readable during the day in full sunlight and their lighting levels can be balanced with the rest of the cockpit.
(iii) Ensure installation of the required flight instruments. Review the appropriate operating regulations (e.g., §§ 91.205(h) and 135.159, or the civil aviation authority equivalent) for required instruments. The type of operation the NVIS-modified aircraft is intended to support dictates where certain instruments are located. For example, to support helicopter medical services, the aircraft's radar altimeter should be located in the instrument panel as close as possible to the pilot's lateral primary field of view and vertically where pilots can easily view it from underneath the NG without having to lift or turn Page MG 16-5
AC 27-1B, Chg 7 2/4/2016 their heads to bring it into unaided view. Instruments the pilot uses to fly the aircraft should not be placed on the far side of the instrument panel from the pilot's seated location.
(iv) Ensure the cockpit can support pilots wearing helmets and NVGs in both the stowed and operational positions as follows:
(A) Pilots are able to sit in a normal posture in the cockpit and move their head with NGs in the operational and stowed positions without hitting cockpit or cabin structures.
(B) Pilots are able to scan across their entire field of regard with NVGs in an operational position and not hit cockpit or cabin structures.
(C) Previous modifications to the cockpit have not introduced structures that will occlude the NVG field of view.
(v) Ensure external modifications that can reflect light into the cockpit, such as wire strike kits or external load mirrors, are modified to support NVG operations. If not, then document those items and mitigations developed as part of the NVIS lighting modification.
(vi) Perform a failure analysis in accordance with section 27.1309 of this guidance to ensure the NVIS lighting system design does not introduce hazards to the aircraft.
(A) The failure analysis should identify NVG-compatibility hazards that may occur if the NVIS lighting (or another aircraft system that can affect NVG compatibility) fails in such a manner as to introduce incompatible light into the cockpit or into the NVGs' field of regard. The integrity level of the system is required to be commensurate with the assessed failure condition classification. The RTCA Document DO-275 defines the design assurance for NVIS lighting. Complete loss of the NVIS lighting system is classified as major, and therefore its loss shall be improbable. Inadvertent or uncommanded actuation of NVG incompatible light sources is classified as severe-major/hazardous, and therefore must be extremely remote. Design consideration should take into account that component failures and system design be failsafe. For instance, any incompatible lighting switch should include design features that prevent inadvertent activation, such as a lever lock or guarded switch. In addition, for designs that install a stand-alone alternate lighting system instead of altering the aircraft's original lighting system, the hazard classification for the failure of the stand-alone alternate lighting system should be the same as that for a lighting system on a VFR aircraft.
(B) One successful method used a single lighting system with NVIS white compatible lighting as the interior lighting source for both the cockpit and passenger cabin, which is useable for both unaided and aided flight. NVIS lighting that incorporates both conventional (non-NIS) and NVIS lighting sources requires an SSA to identify the hazards of inadvertent or un-commanded change to non-NVIS lighting in both the cockpit and cabin. The NVIS lighting system must support transition from aided to
(5) Mechanical installation. The designer should observe good engineering practices in specifying material type, wire routing, fastener type, light switches and controls, edge distance, and ergonomic considerations. If the NVIS lighting design involves modification of another manufacturer's installed equipment, the designer should adhere to the manufacturer's recommendations regarding
(6) Required equipment, instrument arrangement and visibility.
(i) In addition to the instruments and equipment required for flight at night, the following additional instruments and equipment will typically be necessary for NVG operations (to be defined for each helicopter). Review applicable operational regulations that specify aircraft equipment required for Page MG 16-6
(A) NVIS lighting.
(B) Helmet with suitable NVG mount for each pilot and crewmember required to use NVGs.
(C) NGs for each pilot and crewmembers required to use NVGs.
(D) Radar altimeter with suitable low height and failure indications.
For applicants who want EASA to validate their STCS, the applicant may want to notify the operator that a digital readout only radar altimeter will not meet EASA requirements and that the operator should ensure installation of the appropriate radar altimeter.
(E) Slip/Skid indicator.
(F) Gyroscopic attitude indicator.
(G) Gyroscopic direction indicator or equivalent.
(H) Vertical speed indicator or equivalent.
(I) Communications and navigation equipment necessary for the successful completion of an inadvertent IMC procedure in the intended area of operations.
(J) Any other aircraft or personal equipment required for the operation (e.g., curtains, NVG stowage, extra batteries for NVGs).
(ii) The mounting position of all instruments, switches, position labels, and controls should be visible to the pilot during unaided and aided flight and in all cockpit lighting conditions (day and night).
Instruments required for NVG operations should be located in or as close as possible to the pilot's primary scan. For example, a radar altimeter, which is required for NVG operations, should be located as close as possible to the primary instrument cluster. Locating the radar altimeter on the opposite side of the instrument panel increases the pilots' scan and workload. The instruments, switches, and placards should be free from reflections. Warning, caution, and advisory annunciation devices should be conspicuous, NVG compatible, and clearly visible to the pilot (day and night). Gauge and instrument markings should be clearly seen and the colors of the markings maintained. Limited NVG visual degradation of one element on the USAF Tri-Bar chart (12 %) is allowed tor master caution, master warning, and warning messages or annunciators since these lights need to attract the pilot's attention.
Other than master caution and warning lights and warning annunciators, no other light or reflection in the cockpit may degrade NVG visual acuity from the acuity measured viewing the target through the windscreen. Find a copy of the USAF Tri-Bar chart in the checklists at:
(iii) Interior Lighting. Internal lighting systems should not adversely affect the performance of the NVG. NVIS-modified instrument lights, illuminated instrument markings and applicable signs must comply with § 27.1381. Compliance should be demonstrated during both aided and unaided operations.
in past applications, the use of NVIS White provided good color discrimination on instrument markings. If a piece of equipment, instrument, switch, indicator, or panel was illuminated prior to the NVIS lighting installation, it should be illuminated by the NVIS lighting modification. Shades of red, amber, or green in the cockpit that are difficult to distinguish as red, amber, or green in all lighting conditions are not acceptable since pilots must be able to readily distinguish all aircraft cautions, warnings, advisories, and instrument markings without confusion. Similarly, NVG filtering should not result in different colored illuminations becoming difficult to distinguish from each other. For example, when using amber for cautions, the NVIS filtering should not result in amber caution lights and green advisory lights appearing similar in color. Because technology is available that allows "NVG-friendly" reds to appear red without interfering with Class B NVGs, the use of NVIS-Red (which appears orange or amber to the eye) is not Page MG 16-7
AC 27-1B, Chg 7 2/4/2016 acceptable when warning indicators in the cockpit are red. Additionally, NVIS-Red with orange hue is not acceptable in cockpits with amber caution lights or indicators since they are similar in color. Interior cabin, passenger, or emergency lighting should not interfere with NVG operations. Relying on a curtain between the passenger compartment and cockpit may not be acceptable as the sole means of keeping incompatible light from the cockpit if there are incompatible lights in the passenger cabin. Modifying the passenger cabin lighting with NVIS lighting would be recommended, due to the possibility of unacceptable light leaks, hot spots, and glare. Additionally, should a passenger or crewmember move the curtain, the glare and reflections could compromise pilot performance while using NVG.
(7) Exterior lighting. External lighting systems should not adversely affect the performance of the NVIS. The external lighting modifications must comply with §§ 27.1383 through 27.1401 and should use the guidance in AC 20-74. Evaluate external lighting under probable terrain, illumination, and environmental operating conditions. Non-NVIS position lights may cause unacceptable shadowing and interference with NVG performance in dark areas where there is little or no cultural lighting. NVIS-friendly position and anti-collision lights may be required. Landing lights and searchlights should be usable in the visible light mode. If a dual mode visible, IR landing, or searchlight is provided, the visible mode should be the default mode to allow the crew to more easily transition to unaided flight in case of NVG failures.
The crew should be able to illuminate landing zones sufficiently to allow unaided landing or obstacle identification and clearance in the event they need to transition to unaided operations.
(8) Reflections and glare. There should be no glare or reflections that interfere with unaided or NVG aided operations. Sources of reflection and glare could include aircraft interior surfaces (floor, panels, etc.), equipment, seats, etc. There must be demonstrated compliance with §§ 27.773, and
27.1381 in the ground and flight test.
(9) Controls.
(i) NVIS lighting controls should be readily identifiable and accessible.
(ii) NVIS control design should prevent the inadvertent selection of incompatible light sources in the cockpit. Typically, the use of a guarded or locking switch that does not allow inadvertently pushing of the switch to the incompatible light position is acceptable. If there is a capability to select an NVIS incompatible light source, the detrimental effects of incompatible light sources on the external view through the NVG should be evaluated. Some aircraft displays will power-up or re-boot in an NVG incompatible mode and require pilot action to select the NVG mode. This may be problematic should it interrupt power to a display in flight, and thus any possible effect on NVG performance should be
(ili) NVIS lighting should have a dimming range consistent with aided and unaided operations.
Compliance with §§ 27.771(a), 27.773, 27.1301, 27.1309, and 27.1381 must be demonstrated to ensure lighting balance does not unacceptably increase pilot concentration or fatigue. Lighting balance is important to assist in under-the-NVG scan. Native aircraft lighting may not have sufficient balance control to support NG operations.
(iv) Some installations incorporate master light switches to control special busses for the lighting systems. If providing this capability, it should be evaluated to ensure failure modes are not introduced that will result in the illumination of incompatible light sources or loss of all required lighting.
(v) If IR lighting is installed in conjunction with the visible lighting systems required by §
27.1385, the design must ensure that the control for the IR system does not turn the visible lighting system off when the IR system is activated.
(10) NVIS power sources. Determine whether the electrical power source capacity is adequate for the system installation under all foreseeable operating conditions including engine failure. Duplicate systems should be powered from separate busses and, in some cases, from independent sources if required by the airworthiness regulations (see §§ 27.1309 and 27.1351).
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(11) NVIS cockpit and NVG integration.
(1) Accessibility and workload.
(A) The NVIS configuration should not compromise the ability to perform all necessary duties. Consider scanning and control accessibility. The applicant should determine the representative flight profiles and environmental conditions under which the workload should be evaluated. The purpose of this evaluation is to ensure that the workload associated with NVIS operations does not compromise safety of flight. It is important to assess the lighting system's support of transition from aided flight to unaided flight. Demonstrate compliance with §§ 27.771, 27.773, 27.777, and 27.1523. Carefully consider the installation suitability for single pilot operation taking into account workload, cross cockpit view, and reduced field of view with the consequent need for greater head movement.
(B) If taking credit for the use of the landing light, this should be selectable and controllable without removing either hand from the primary flying controls.
(C) The design of the NVIS should consider flight into inadvertent IMC, unusual attitude recovery, and the transition from aided flight to instrument flight. This will also address the consequences of loss of external view through the NVG. Therefore, the applicant should plan this evaluation during all phases of aided flight (such as cruise flight or takeoff and landing, if requested) to ensure that workload is acceptable and the required instruments are within the pilot's primary scan.
(D) Assess the NVIS lighting for readability, uniformity, balance, light leakage, reflections, and degradation of NVG performance. See the NVIS and NVG cockpit integration checklists at http://www.faa.gov/aircraft/air_cert/design_approvals/rotorcraft/nvis/. In addition, RTCA Document DO-275, section 4.0, provides an expanded explanation. Assess the cockpit using the make, model, and part number of the NVG that the applicant intends to show that are compatible with their NVIS lighting
(il) Controls.
(A) Accessibility of NVIS lighting system controls. Pilots should be able to readily identify, access, and operate, with one hand, the NVIS lighting controls in-flight from their normal seated position.
(B) Inadvertent actuation of controls. Provide appropriate protection to prevent the inadvertent actuation of NVIS lighting controls and non-NVIS light sources.
(iii) Visibility.
(A) Windshield. The windshield and transparencies should not decrease NVG light sensitivities more than 12% (equivalent to one resolution element on a tri-bar chart). If the aircraft has a windshield anti-ice function, the visibility should be evaluated with anti-icing on and off to assess effect on the NVGs. Operation of windshield anti-ice should follow manufacturer's procedures and limitations.
(B) Glare and reflectivity. Internal and external light sources can produce glare and reflectivity.
(C) Internal light sources.
(1) Reflections should be no worse than the original unaided lighting. However, NVGs may pick up more reflections than seen with unaided vision. Additionally, NVIS-incompatible light sources in other areas of the aircraft can cause interference. Block those reflections to ensure they do not interfere with the pilot's ability to see outside the aircraft while wearing NVGs.
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(2) Glare is an indication of an NVG-incompatible energy emission. Glare can result from poorly filtered or fitted lighting. Assess light sources causing glare and develop mitigating solutions to keep them from interfering with the pilots' view through NVGs.
(D) External light sources.
(1) Assess external light glare and reflectivity during the night flight for both unaided and aided operations. Evaluating the effects of glare and reflections that interfere with NVGs from external aircraft lighting is very important when operating in remote, dark areas. There are NVIS lighting position and anti-collision lights available. Consider using them if operations are conducted in very dark areas where there is little to no ambient cultural lighting.
(2) Methods to reduce glare or reflections caused by external aircraft lighting depend on where the light enters the cockpit and what aircraft structure reflects the light. For example, light that reflects off skids or wire cutters might be mitigated by using non-reflective paint on the reflecting surfaces.
If using physical barriers or baffle materials to block glare from entering the cockpit, pay particular attention to restrictions in the pilot's field-of-view through the chin bubble, particularly during take-off, landing, and hover operations. Also, pay attention to the potential of the mat or baffle moving or dislodging during flight, thereby causing interference with the tail rotor pedals or other aircraft controls.
(3) Use of blocking methods should be evaluated during both ground and flight test.
It is possible that a non-compatible landing light used for NVG aided landings, which was found to be acceptable when landing on grass or a dark surface (e.g., asphalt), could cause unacceptable reflections when used over a light-colored concrete surface. For this reason, evaluate the effect of the light's reflection off of various ground surfaces such as asphalt, concrete, etc., over which the aircraft may operate.
(4) Evaluate external light sources that pilots could use to assist them with NVG flight for their effect on NVG performance. Assess any installed landing lights, searchlights, etc., to determine their effect on the aided visual range. For instance, if the pilot uses a searchlight or landing lights to help assess a landing area or while landing with NVGs, then the light's effect on the range of vision within and beyond the light boundaries should be evaluated and documented.
(5) During integration evaluations, record sources of non-compatible light glare and reflections and any mitigating strategies developed.
(12) Ground and flight tests.
(i) The purpose of FAA certification tests is to verify that the rotorcraft meets the certification requirements for both aided and unaided operations. Testing will include a ground and flight assessment of crew stations to ensure that the crew can use all systems for both aided and unaided operations.
These assessments may result in changes to the limitations or operating procedures in the RFMS.
(il) Prior to requesting FAA certification flight tests, the applicant should submit the certification plan, ground and flight test plans, and type design details (to include relevant data, drawings, bench tests, component tests, environmental qualifications, installation configurations, and test equipment and calibration) that were used to demonstrate compliance with the requirements. It is highly recommended that the applicant and installer perform ground day, night, and NVG-aided evaluations prior to the FAA's evaluations.
(Ili) Ground and flight test plans should include the types of operations for which the applicant intends to use the aircraft. For instance, dual pilot operations or training will require both a right and left pilot seat evaluation. Emergency medical service (EMS) aircraft, for example, require an evaluation of visibility within the passenger compartment and the adequacy of cockpit protection from passenger compartment lighting if those lights are not NG compatible.
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(iv) The FAA will review the data package to verify compliance. After certification package acceptance, the applicant should coordinate the FAA ground and flight test plan and test schedule. The test plan and schedule should include all proposed tests to show compliance. RTCA Document DO-275, section 4.0, and its appendices describe one acceptable method of demonstrating compliance. The checklists found at http://www.faa.gov/aircraft/air_cert/design_approvals/rotorcraft/nvis/ also outline another acceptable test sequence. Upon test plan acceptance, prior to commencing any certification tests (ground or flight), a conformity inspection should be performed. Once the conformity is completed, any changes from the conformed configuration (e.g., removing filters or changing bulbs in light sources) may require another conformity inspection at the discretion of the certification office.
(v) The applicant is responsible for meeting all pre-test requirements and providing the FAA certification office with the following:
(A) A list of test equipment the applicant will use (i.e., tri-bar charts, illumination source, illumination measuring device, NVG test set, or NVG eye lane).
(B) A description of the test facilities to be used (type of darkened location).
(C) A description of the proposed flight area including cultural lighting, terrain, obstacles, and landing areas.
(D) Weather and illumination information including moon cycle, anticipated climatic conditions, etc.
(E) Any additional training necessary to operate in a NVIS environment (novel or new technology briefing).
(F) The flight equipment to be used (helmets, mounts, NVGs, flashlights, etc.).
(vi) Ground Test Procedures.
(A) Conducting ground testing prior to flight testing will optimize the test program and minimize flight test risks. Conduct this evaluation from all crew stations intended to be used (including the cabin) in NVG operations. The power supply used for ground tests, with the aircraft electrical generating system not operating, should provide power representative of flight conditions. Consider using power representative of flight conditions with generator and battery power to assess how the lighting system functions on low power.
(B) Flight-testing should be commenced after satisfactory completion of ground testing.
The schedule should allow for sufficient time between ground and flight test to resolve deficiencies discovered during ground testing. RTCA Document DO-275, section 4.4.1 and its appendices provide one acceptable test procedure and test sequence. Alternatively, as a minimum, complete the FAA Ground NG-Cockpit Compatibility checklist, found at http://www.faa.gov/aircraft/air_cert/design_approvals/rotorcraft/nvis:
(vii) Flight test procedures.
(A) Flight test should be scheduled for a low illumination (no moon) night, preferably in an area where there is little cultural lighting. Evaluation of NVG and NVIS lighting integration should be conducted in low ambient light conditions, because high ambient lighting conditions may mask the effects of inadequate cockpit lighting and reflections or glare.
(B) Prior to commencing the flight test evaluation, a daylight familiarization flight of the flight test area should be performed. Any specific flight regimes, maneuvers, terrain, or landing areas that Page MG 16-11