AC 29-2C, Chg 7 2/4/2016 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.
( ) 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 aide 4 d vi sual 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/AUTHORITY 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.
(ii) Prior to requesting FAA/AUTHORITY 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 requirementsIt is highly recommended that the applicant and installer perform ground day, night, and NVG -aided evaluations prior to the FAA’s evaluations.
(iii) 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 NVG compatible.
(iv) The FAA/AUTHORITY will review the data package to verify compliance. After certification package acceptance, the applicant should coordinate the FAA/AUTHORITY 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/AUTHORITY 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.
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(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 NVG-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 will be used for the NVIS evaluation should be flown to familiarize the test pilots with possible hazards in the test area.
(C) Installing dual controls for every flight test evaluation is recommended, as additional risk-mitigation procedures may be required to conduct the test safely. If it is determined that the normal configuration of the aircraft is required for the flight evaluation, it may not be possible to install dual controls (such as, for example, in a police helicopter where the second crew station is equipped with comprehensive police mission systems). In this case, appropriate training and authorization may be required for the FAA/AUTHORITY test pilot to conduct the in-flight evaluation. The occupant of the second crew position should be a pilot trained in the use of NVGs and familiar with the installation under evaluation. In addition, special test equipment may be installed during the evaluation to enhance flight test safety. Minimum crew should be used to conduct an evaluation. If additional personnel are required for the evaluation, install the appropriate crew stations and safety equipm ent.
(D) The flight test profile should consist of maneuvers representative of those performed during normal or special operations over terrain and cultural areas in various illumination and weather conditions. This test should include evaluation under low illumination conditions (e.g., no moon, and overcast sky, with little cultural lighting). RTCA Document DO-275, section 4.4.2 provides one acceptable test procedure and test sequence. Alternatively, as a minimum, complete the NVIS-NVG Compatibility Flight Evaluation found at http://www.faa.gov/aircraft/air_cert/design_approvals/rotorcraft/nvis.
g. Rotorcraft Flight Manual (RFM) (or Supplement (RFMS)).
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AC 2 9-2C, Chg 7 2/4/2016 An RFMS template is provided on the following pages.
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This section provides one acceptable template for use as a Rotorcraft Flight Manual Supplement (RFMS).
Other formats may be acceptable.
The following is an outline for a flight manual supplement to follow when developing a supplement for a specific STC. Information quoted in bold is expected to be in the RFMS verbatim. Following the headings are advisory and explanatory narratives in italics regarding the type of information you should include.
For example, under “2.1 NVG Compatibility, the explanatory text is not meant to be cut and pasted.
Note: Foreign civil certification authority requirements for flight manual supplement information will not be the same as represented here. If you are considering asking for a validation of your STC with, for example, EASA or TCCA, you may need to modify your RFMS. Coordinate with the appropriate foreign validation point of contact responsible for your project.
1. GENERAL. Include the following or similar statement:
“Any future modification, including role or mission specific equipment, involving a light emitting or reflecting device requires reassessment of the cockpit to ensure its compatibility with night vision imaging system (NVIS) operations.”
2. LIMITATIONS.
Add the following limitation if the aircraft has category A procedures and category A profiles were not certificated as part of the NVIS approval.
“Category A operations are prohibited when using NVG”
2.1 NVG Compatibility. The following NVGs are compatible with this cockpit lighting system: In this section, list the make and model of the NVGs used to determine compatibility. For example, if the STC holder shows its lighting system is compatible with ITT F4949 Class A and B NVGs, L- 3 M949, Class A and B NVGs, and Nivisys NVAG 6 NVGs, then the NVG compatibility list can be as follows.
2.1.1 NVGs that meet the performance requirements of TSO-C164. This covers NVG manufactured under a TSOA. 2.1.2 <Make, Model, and Part No. of NVG>. List the ITT/ExcelisF 4949 and Litton/Northrop-Grumman/L-3/Insight M949 NVG part numbers used to determine compatibility. If the STC is a foreign validation, coordinate with the validating authority to add foreign NVGs found compatible with the lighting system.
(NOTE: If the STC holder’s NVIS lighting system is shown to be only compatible with Class B NVGs, then add a limitation to use only Class B NVGs.)
2.2 Operational Limitations.
Include the following or similar limitation. This limitation may be different for RFMS’ acceptable by foreign authorities. Coordinate with the foreign authority for required wording:
“Installation of this NVIS lighting system does not approve flight operations with night vision goggles (NVG). The operator must coordinate with their FAA Flight Standards District Office to obtain operational authorization.”
2.3 Additional Required Equipment Functioning Correctly for NVG Operations (define this for each helicopter).
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AC 29-2C, Chg 7 2/4/2016
2.3.1 Vert ical speed indicator or equivalent.
2.3.2 List other aircraft equipment identified in the STC required for NVG operation like curtains separating the cockpit from the passenger cabin, chin bubble mats, etc.
If a design method (e.g., chin mats) is used to block the light from entering the cockpit, a caution such as the one below may be required. Only add requirements for chin mats or other light blocking items, like curtains, if they are required by the STC. Do not add generic statements or “if needed” statements to the limitations section of the RFMS.
“CAUTION:
Ensure <e nter chin mats, or whatever is used to block chin bubble light> are positioned and secured properly, allow sufficient view out of the chin bubble, and that they do not block or restrict operation of the flight controls.”
2.4 Minimum Crew. For foreign certifications, check with the foreign authority for correct wording.
2.4.1 Additional crewmember use of NVGs during single-pilot operations into and out of unimproved sites:
2.4.1.1 Landing. An additional NVG trained crewmember must be equipped with and use NVGs during landing to assist in obstacle identification and clearing.
2.4.1.2 Takeoff. An additional NVG trained crewmember must use NVGs during takeoff from unimproved sites to assist in obstacle identification and clearance if operational conditions permit (i.e., patient status allows).
2.5 Incompatible NVIS Lights. Specifically identify installed lighting in the cockpit and cabin that the STC did not modify and that are not useable during NVG operations. Additionally, include instructions on the use of non-NVIS lighting modified carry on equipment (e.g., cell phones, mission equipment, medical equipment) during NVG operations. For example, instructions should be the following or similar:
“Use of non-NVIS modified carry-on or personal equipment in the cockpit is prohibited during NVG operations”.
“The pilot must coordinate with other crewmembers and passengers before the use of non-NVIS modified carry-on equipment is used during NVG operations.”
3. EMERGENCY AND MALFUNCTION PROCEDURES.
3.1 NVG Malfunction or Failure. Describe procedures for NVG failure and for transition from aided to unaided flight, as may be required.
3.2 NVIS Lighting Malfunction or Failure in Flight. Describe procedures for handling NVIS lighting malfunctions, including procedures if the malfunction or failure degrades NVIS compatibility.
4. NORMAL PROCEDURES. Provide configuration and check procedures to ensure aircraft is capable of NVG operations. Suggested procedures are:
4.1 Operational Procedures.
4.1.1 Preflight.
• Check windshield, windows, and chin bubble windows for suitability (e.g., scratches, crazing, cleanliness).
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• Check filter condition for fogging, crazing, cracking, etc., which impairs unaided readability of the instrument or gauge to which the filter is applied.
• Check NVIS lighting for light leakage and compatibility.
• NVG adjustment and alignment.
• Check function of additional NVIS equipment.
• Interior configuration check for NVIS equipment (e.g., deselect incompatible light sources).
• Exterior configuration check for NVIS equipment (e.g., position lights, taxi and landing light, search light are selected to correct mode, if applicable).
• Adjust lighting as required.
4.1.2 In-flight.
• Control of cockpit and external NVIS illumination. Adjust lighting, as required.
• Transition to aided from unaided operations (and vice versa), as necessary.
• Radar altimeter and additional equipment procedures, as necessary.
4.1.3 Post flight. Report NVIS lighting or equipment and windscreen/transparency discrepancies.
5. WEIGHT AND BALANCE. The weight and balance should include the installation of NVIS equipment. Provide a sufficiently detailed system description. Refer to AC 43.13-1B, Chapter 10 for additional guidance.
(End of the section of one template for use as an RFMS.)
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AC 29-2C, Chg 7 2/4/2016
h. Instructions for Continued Airworthiness (ICA).
(1) General. ICA must contain the information necessary for carrying out ongoing maintenance and inspections on NVIS equipment installed in the rotorcraft. Refer to section AC 29.1529 and Appendix A of this guidance RTCA Document DO-275, section 5.5, also contains information related to the development of NVIS lighting ICA’s. . At a minimum, the following should be included:
(i) Appliance, system or accessory maintenance manual, or section.
(ii) Maintenance Instructions and Inspection Requirements. Ensure that the ICA instructions are clear on whether the operator must remove the filter or other NVIS modification prior to returning an instrument, gauge, or light to the manufacturer for maintenance. Ensure the ICAs have sufficient instructions on how to de-modify and re-modify instruments and gauges. Additionally, we recommend periodic inspections to ensure the NVIS lighting system is still NVG compatible and the configuration of the aircraft still agrees with the approved data. One acceptable method is the inclusion of an annual or time-interval inspection procedure..
(iii) Airworthiness Limitations.
(iv) Illustrated Parts Breakdown. The ICA should cover (as a minimum) aircraft transparencies (windscreen, windows, etc.), NVIS lighting, and any additional aircraft equipment that support NVIS operations. The NVG manufacturer should have ICA and maintenance schedules f or its goggles that the operator should follow.
It is recommended that a storage location or compartment is provided on the aircraft to protect the continued airworthiness of the NVGs. However, storing the NVGs in a location that could cause damage to the aircraft or an aircraft component, hinder crashworthiness, or result in loss of the intended function of a component is prohibited.
(2) Modifications or Maintenance.
(i) Post - Type Certificate (TC) or STC Approved Modifications. Any subsequent aircraft modifications (internal or external), including operational equipment (FLIR, EMS equipment, etc.)
involving a light emitting or reflecting device should be considered major since it could affect the operational characteristics of the NVIS lighting system and should be re-assessed against the original requirements for the NVIS certification.
(ii) Multiple TC or STC Approvals. If an approval is granted for multiple aircraft, installation and production procedures should ensure all aircraft comply with the type design. Provide this information in the initial certification data package so that the FAA knows it is intended for multiple approvals. The production procedures should be sufficiently detailed to detect minor differences between the different aircraft. Expect that post-production tests will include the ground and flight tests described above for each individual aircraft.
(iii) STC and Type Certificate Data Sheet (TCDS) verbiage: The following verbiage was developed to help with f.(2)(i) and f.(2)(ii) above and should be included in the “Limitations” section of the STC and the TC TCDS:
“Any deviation from the cockpit or cabin configuration specified in the STC or TC Type Design may affect the compatibility of the NVIS and will require a re-evaluation for NVIS cockpit and NVG compatibility. The aircraft is not certificated for NVG operations until the evaluation is completed.”
Note: Find the NVIS/NVG cockpit evaluation guides/checklists at http://www.faa.gov/aircraft/air_cert/design_approvals/rotorcraft/nvis.
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CHAPTER 3
AIRWORTHINESS STANDARDS
TRANSPORT CATEGORY ROTORCRAFT
MISCELLANEOUS GUIDANCE (MG) AC 29 MG 17 GUIDANCE ON ANALYZING AN ADVANCED FLIGHT CONTROLS (AdFC) SYSTEM
a. Purpose.
(1) This MG provides certification guidance for installation of an AdFC system in rotorcraft. An AdFC is a flight control system that utilizes or replaces mechanical parts in conventional mechanical flight control systems with electronic parts such that there is no remaining direct mechanical link from the pilot to the control surfaces or swashplate.
Typical systems include fly-by-wire and fly-by-light. For the purpose of this document, conventional limited-authority or full-authority stability augmentation systems are not considered a subset of AdFC.
(2) This MG describes acceptable guidance for analyzing an AdFC system to determine compliance with all applicable sections of 14 CFR part 29. An applicant for a type certificate, amended type certificate, supplemental type certificate, amended supplemental type certificate, and technical standard order authorization may use the “Rotorcraft Advanced Flight Controls (AdFC) Handbook” (being published under Policy Statement PS-ASW-27,29-09), in conjunction with applicable ACs, to comply with relevant regulations.
b. References and Related Documents.
(1) Applicable 14 CFR part 29 regulations:
29.141, 29.143, 29.151, 29.161, 29.171, 29.173, 29.175, 29.177, 29.241,
29.391, 29.395, 29.397, 29.399, 29.602, 29.663, 29.671, 29.672, 29.674,
29.675, 29.681, 29.683, 29.685, 29.687, 29.771, 29.773, 29.777, 29.779,
29.1301, 29.1309, 29.1317, 29.1321, 29.1322, 29.1329, 29.1335, 29.1351,
29.1555, 29.1581, 29.1585, and Appendix B
(2) Applicable ACs (current version):
(i) AC 20-174, Development of Civil Aircraft and Systems.
(ii) AC 20-175, Controls for Flight Deck Systems.
(iii) AC 29-2, section 29.1309; Equipment, Systems, and Installations.
(3) Applicable Orders (current version):
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AC 29-2C, Chg 5 6/13/2014
(i) 4040.26, Aircraft Certification Service Flight Test Risk Management Program.
(ii) 8110.4, Type Certification.
(4) Applicable guidance:
(i) Policy Statement PS-ASW-27,29-09, Rotorcraft Advanced Flight Controls (AdFC) Handbook.
(ii) SAE, International ARP 4754A, Guidelines for Development of Civil Aircraft and Systems.
(iii) SAE, International ARP 4761, Guidelines and Methods for Conducting the Safety Assessment Process on Civil Airborne Systems and Equipment.
c. Background. The FAA recognizes that technology utilized in commercial rotorcraft consistently lags behind state-of-the-art air transport aircraft and military technologies. AdFC technology has been in use for many years, but guidance material on the safety aspects of certification, continued operational safety, and especially the use of that technology has been limited within the FAA.
d. Application. Applicants seeking approval for the installation of an AdFC system in rotorcraft should apply this guidance as a means, but not the only means, for showing compliance with the applicable rules.
(1) Since part 29 regulations are inadequate for addressing the new and novel features of AdFC systems, special conditions, equivalent means of compliance, and methods of compliance issue papers may be required to establish safety standards in the following areas:
(i) Interaction of Systems and Structures. Since rotorcraft with AdFC systems may contain control functions that affect the structural integrity of the rotorcraft, additional safety considerations are necessary to address the effects of these systems on structural integrity, either directly or because of AdFC failures.
(ii) Pilot and Co-Pilot Dual Controls. Since the current regulations address mechanically linked controls only, additional safety considerations are necessary to address potentially confusing aspects of pilot and co-pilot dual, non-linked controls. As an example, a non-responsive control input could prevent compliance with § 29.779.
(iii) Lateral-Directional and Longitudinal Stability and Low Energy Awareness.
An AdFC allows for many possibilities in developing laws for novel flight control. In the simplest form, an AdFC could replace the function of a direct link between the flight controls and the swashplate. The current requirements were written with the conventional systems of the rotorcraft handling qualities in mind. A more likely situation Page MG 17 - 2
is the use of an AdFC to modify the relationship between control input and rotorcraft response.
(iv) Control Margin Awareness. Additional safety considerations are required to address pilot awareness when employing AdFC systems since certain provisions of § 29.143 are not adequate for AdFC systems.
(v) Flight Characteristics Compliance via the Handling Quantities Rating Method (HQRM). Additional safety considerations are required to address a methodology for compliance with § 29.1309 by using the HQRM to show an HQ rating of “satisfactory” for flying qualities in degraded modes.
(vi) Flightcrew Alerting. Additional safety considerations are required to address the unique alerting characteristics of AdFC systems. The current regulations may be inadequate to handle the display of possible degraded modes where a pilot needs to be aware of the state of the primary flight controls.
(vii) Data Integrity. Additional safety considerations are required to ensure that the primary signals from the flight control system cannot be altered unintentionally, that the altered signal characteristics will maintain stable gain and phase margins with sufficient power to each axis, and that un-commanded signals are extremely improbable.
(viii) Flight Envelope Protection (FEP). Additional safety considerations ar e required to ensure that an FEP system, if implemented, prevents the pilot or autopilot from making control commands that would force the aircraft to exceed its structural or aerodynamic operating limits.
(2) Evaluation Methodology. There should be an evaluation of the AdFC system’s performance, the same as with conventional flight control systems, to demonstrate adherence to the safety requirements under all failure conditions. In each case, the software and hardware used must be under configuration control to comply with the regulations. We recognize the following evaluation methods; however, there may be other acceptable methods:
- Computer Analysis.
- Pilot-in-the-Loop Simulator Test.
- Bench Test.
- Ground Test.
- Flight Test.
(i) There may be a relationship between the levels of integrity provided to satisfy a determined failure condition category and the methodology used to validate the adequacy of the provided integrity. The below table, Figure AC 29 MG 17- 1, addresses this relationship:
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AC 29-2C, Chg 5 6/13/2014 Failure Condition Categories Suggested Verification Method Possible Additional Methods Minor Analysis Flight Testing *3 Major Analysis Ground Test Simulation Flight Test Hazardous/Sever e-Major Analysis Ground Test Limited Flight Tests *1 , *2 Simulation Catastrophic Analysis Simulation Ground Test Limited Flight Tests *1 , *2 * - Notes:
1 - This should be determined on a case-to-case basis.
2 - Minimize flight testing as a verification methodology, for this combination of provided integrity and failure condition category, due to safety in testing considerations. However, desirable flight testing may be feasible for some aspects if observing proper identification of flight test risk and assessments, and risk mitigations, in accordance with FAA Order 4040.26.
3 - For analysis or verification, those probable failures evaluated as having minor effects, flight testing is an option if the effects are not obvious or if there can only be evaluation of closed loop effects in flight.
Figure AC 29 MG 17-1 Verification Methodology
(ii) Due to AdFC inherent complexity, AdFC systems that typically have a large number of test cases of single and multiple failures should be investigated to verify the safety functions under all failure conditions.
(A) Non-Real Time Computer Analysis. At the beginning of the development process, when system components are not yet available in hardware, non-real time computer simulation is a useful tool for supporting the preliminary system safety assessment. This allows, at an early stage of the development, a prediction of the effects and an assessment of the criticality of failure modes of the flight control system.
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(B) Pilot-in-the-Loop Simulator Test. It may be practical to use a flight simulator (FS) to qualitatively verify safety assessments for certain AdFC failure conditions that would be high risk or unsafe to perform in flight. These assessments may be part of the SA process used to show compliance with specific regulations. For example, use the FS to gather data on aircraft transients caused by a failure, crew recognition of the abnormal event, recoverability after the failure transient, and the ability to continue safe flight and landing after recovery. There can be accomplishment of these assessments for critical, selected conditions using the FS without presenting a safety risk to the flight test crew.
(1) Test Environment. The test environment for pilot -in-the-loop simulator tests includes:
- Cockpit, equipped with AdFC representative displays and controls.
- Computer Generated Imagining (CGI).
- Simulated AdFC system.
- Simulated rotorcraft visuals and behavior.
(2) Verification of Simulation Tools.
(i) Before final evaluation of failure mode effects using a FS, validate the FS for the specific test conditions identified in the test plan. This validation may be done quantitatively, qualitatively, or both and must be in a manner suitable to the FAA..
(ii) There should be control of the FS configuration, including hardware and software, to ensure there is no corruption of the functional performance, as validated, during the certification process. The FS should be assessed to identify and preclude opportunities for misleading simulator results that could affect the certification process and ultimately the design of the AdFC systems.
(3) Test Procedure and Expected Results. The test procedure for pilot -inthe-loop simulator tests includes real-time simulation of performance with simulated failures. The expected test results are:
(i) Evaluation of pilot intervention time (recognition and reaction time) for the occurrence of failures under various flight conditions.
(ii) Assessment of handling qualities during recovery maneuvers.
(iii) Assessment of man-machine interface (controls and displays, warnings, cautions, and advisories).
(iv) Evaluation of rotorcraft transients.
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