Staff Instruction (SI)

Certification of Night Vision Imaging Systems

File No.: 5009-32-0 SI No.: 513-011
RDIMS No.: 1227010 -V12 Issue No.: 01
Issuing Branch: Aircraft Certification Effective Date: 2006-12-18
Activity Area: Qualifying    

1.0 INTRODUCTION

1.1 Purpose
1.2 Applicability
1.3 Description of Changes

2.0 REFERENCES AND REQUIREMENTS
2.1 Reference Documents
2.2 Cancelled Documents
2.3 Definitions and Abbreviations

3.0 BACKGROUND

4.0 DESIGN APPROVAL PROCEDURE

5.0 TEST PROGRAM
5.1 General
5.2 Aircraft Ground Test
5.3 Aircraft Flight Tests

6.0 TEST PROCEDURES
6.1 Daylight Readability of Cockpit Displays
6.2 Nighttime Readability of Cockpit Display
6.3 NVG-Aided Visual Acuity
6.4 NVIS Radiance
6.5 Aircraft Mounted External Light Source Evaluation
6.6 Crew Station Layout Assessment
6.7 Field of View Assessment

7.0 SAFETY CONSIDERATIONS

8.0 OPERATIONAL APPROVAL

9.0 CONTACT OFFICE



1.0 INTRODUCTION

1.1 Purpose

The purpose of this Staff Instruction (SI) is to provide guidance for the certification of aircraft for Night Vision Imaging Systems (NVIS) operations under Visual Flight Rules (VFR).

1.2 Applicability

This document is applicable to Transport Canada Civil Aviation (TCCA) Headquarters and Regional Aircraft Certification personnel, including delegates.  

1.3 Description of Changes

This SI is issued as a revision to Aircraft Certification Policy Letter (ACPL) No. 29 Issue 1 in order to provide information regarding the specific differences and/or additional TCCA expectations with respect to the FAA ACs in paragraph 2.1(g) and (h) below.  The scope of the document, which now applies to all aircraft, is also changed to provide guidance on test programs and procedures. 

2.0 REFERENCES AND REQUIREMENTS

2.1 Reference Documents

It is intended that the following reference materials be used in conjunction with this document:

  1. Staff Instruction (SI) 513-008-Flight Test Division Support of Regional Flight Test Activities;
     
  2. SI 513-007-Approval of Domestic Modifications and Repair Design;
     
  3. Advisory Circular (AC) 513-003-Flight Test Considerations for the Approval of the Design of Aircraft Modifications;
     
  4. AC 513-004-Flight Manual Requirements following Modifications;
     
  5. Commercial & Business Aviation Advisory Circular (CBAAC) No. 0251-Use of Night Vision Imaging Systems in Helicopter Operations;
     
  6. Commercial & Business Aviation Policy Letter No. 176-Approval of Night Vision Imaging Systems Programs utilizing Night Vision Goggles;
     
  7. Federal Aviation Administration Advisory Circular (FAA AC) 27-1B-Certification of Normal Category Rotorcraft-Miscellaneous Guidance (MG) 16-Certification Procedure for Rotorcraft Night Vision Imaging Systems (NVIS) Lighting Equipment;
     
  8. FAA AC 29-2C-Certification of Transport Category Rotorcraft-MG 16-Certification Procedure for Rotorcraft Night Vision Imaging Systems (NVIS) Lighting Equipment;
     
  9. Federal Aviation Administration Technical Standard Order (FAA TSO) C-164-Night Vision Goggles; and;
     
  10. MIL-L-85762A-Lighting, Aircraft, Interior, Night Vision Imaging System (NVIS) Compatible;

2.2 Cancelled Documents

As of the effective date of this document, ACPL No. 29, Issue 1, dated 2000-09-19—Use of Night Vision Imaging System (NVIS) – Helicopter Operations is cancelled.

2.3 Definitions and Abbreviations

  1. Night Vision Imaging System (NVIS) - A system which uses image intensifier tubes to produce an enhanced image of a scene in light conditions too low for normal navigation and pilotage.
     
  2. Night Vision Goggles (NVG) - These are goggles that pick up any light in the immediate area and amplify it several thousand times using an image intensifier. This works by the photoelectric effect. As a photon collides with a detector plate, the metal ejects several electrons that are then amplified into a cascade of electrons that light up a phosphor screen.
     
  3. Heads Up Display (HUD)
     
  4. Visual Acuity (VA).
     
  5. NVIS Radiance (NR) - NVIS radiance is the amount of energy emitted by a light source that is visible through NVIS.
     
  6. Class B - Is a class of NVG that contains an objective filter that prevents light waves measuring below 665 nanometres from entering the image intensifier.
     
  7. Forward Looking Infrared Radar (FLIR).
     
  8. Transparencies - Window, windscreen, chin bubbles and overhead windows installed on the aircraft that the crew uses to look outside the aircraft.

3.0 Background

2. In the past most civil aircraft have been certificated for unaided night flight.  All aircraft certificated for NVIS operations have explicit statements that NVIS or NVG operations are approved, and this information is contained in the “limitations” section of the applicable Aircraft Flight Manual (AFM) or AFM Supplement.

4.0 DESIGN APPROVAL PROCEDURES

1. Although the FAA ACs 27-1B and 29-2C pertain to certification procedures for rotorcraft, MG-16 and this document identifies the procedures for certification of all aircraft for NVIS operations.  Modifications to the aircraft, or to on-board equipment, to achieve NVG compatibility with a particular aircraft is considered a major modification and shall be processed through TCCA Aircraft Certification headquarters or regional office, as appropriate to the applicant, using the procedures described in SI 513-007.

2. NVG are extremely sensitive to the light emitters and reflectors installed in and on the aircraft.  The details of the cockpit configuration, cabin configuration, and external lighting and configuration are critical to the NVG compatibility of each individual aircraft.  Since aircraft internal and external configurations differ between individual aircraft, the certification of an aircraft for NVIS is for an individual aircraft, or a group of aircraft with identical internal lighting, avionics display and configuration, and external lighting and configuration.  An applicant is required to make an application to TCCA as per subsection 4.0(1) if the applicant intends to install a previously approved domestic or foreign Supplemental Type Certificate.

3. FAA AC 27-1B and 29-2C MG-16 are acceptable for use in Canada for NVIS certification procedures.  In addition, however, to the procedures described in SI 513-007, FAA AC 27-1B and 29-2C MG-16, for the certification of NVIS, applicants should provide the following data to aid in determining the extent of ground and flight tests that will be required:

  1. System Safety Analysis for complex systems or Failure Mode Effects Analysis for simple systems;
  2. Draft AFM Supplement using the guidance in AC 513-004;
     
  3. Details of the cockpit configuration including various displays and avionics;
     
  4. Details of both internal and external aircraft lighting;
     
  5. Details of the external configuration of the aircraft including FLIR and mirrors;
     
  6. Additional data, such as drawings or schematics, required to completely describe the configuration; and
     
  7. The technical specifications, equipment model number and performance metrics of the NVG to be certificated in conjunction with the aircraft modification, and whether the NVG meets FAA TSO C164.

5.0 TEST PROGRAM

5.1 General

  1. The test program is conducted in two parts, that is, the aircraft ground test and aircraft flight test.  The purpose of the evaluation is to determine whether the aircraft is compatible with the particular NVG to be used.  The applicant will need to specify which NVG is intended for use in a particular aircraft, and the aircraft will be assessed with those NVG.  The aircraft can be assessed for suitability for NVG aided flight by evaluating the aircraft interior and exterior lighting, crew station layout, and field of view.  The aircraft suitability must be assessed from all crew stations that will require flight crew to maintain a visual scan, using NVG, outside the aircraft for terrain and obstacle avoidance.  This assessment may involve non-pilot crew members.
     
  2. Lighting—Three critical conditions have been identified to assess internal aircraft lighting suitability, and readability of aircraft displays, annunciators and instruments; daylight; night time unaided; and NVG-aided visual acuity.  Exterior lighting cannot be assessed on the ground and must be assessed in flight in an operationally relevant environment.
     
  3. Crew Station Layout—The crew station layout must be assessed to verify that the crew stations can be effectively used under daylight conditions, night unaided conditions, and under night NVG aided conditions.
     
  4. Field of View—The field of view must be assessed to ensure that there are no obstructions which would unacceptably degrade the pilot’s view of the scene outside the aircraft.

5.2 Aircraft Ground Test

1. The aircraft ground test is conducted in a darkened area such that the requirements of section 6.3 can be met and which is sufficiently dark to prevent undesired or outside light sources from interfering with any of the measurements.  The evaluator should scan the area around the target chart to verify that there are not any light sources/reflections that could interfere with the test.

2. The ground test consists of the following as a minimum:

  1. Crew station layout under night unaided and NVG aided conditions, section 6.6;
     
  2. Field of view under night unaided and NVG aided conditions, section 6.7;
     
  3. Night time readability of cockpit displays, annunciators and instruments, section 6.2; and
     
  4. NVG-aided visual acuity, section 6.3.

3. The NVIS radiance test, detailed in section 6.4, will help identify which component or components in the cockpit are causing the problems if problems are noted performing the NVG-aided visual acuity test.

5.3 Aircraft Flight Tests

1.The aircraft flight test can be performed once the ground test has been completed successfully.  The flight test is used to confirm the results of the ground test, to verify daylight performance, and to also assess all aircraft mounted external light sources under night NVG aided conditions.  The aircraft should be flown at operationally representative altitudes, over the expected terrain to assess the effects of aircraft light sources reflecting off the terrain/obstacles.  The night portion of the flight test should be performed under a wide range of ambient light conditions – from bright moonlight on a clear night, to a moonless overcast night far from any built up areas, to a dark night over a brightly lit city.  As a minimum, the aircraft must be flown under a moonless sky, such that the illumination is 1.0 millilux or less, away from any built-up areas.

2. The flight test consists of the following as a minimum:

     e. Crew station layout under daylight conditions, section 6.6;

     f. Field of view under daylight conditions, section 6.7;

     g. Daylight readability of cockpit displays, section 6.1;

     h. Night time readability of cockpit displays, section 6.2; and

     i. Aircraft exterior lighting evaluation, section 6.5.

6.0 TEST PROCEDURES

6.1 Daylight Readability of Cockpit Displays

1. A qualitative assessment of cockpit displays for daylight readability can be performed under operationally representative conditions.  The daylight readability must be assessed whenever the cockpit lighting or displays have been modified to accommodate the use of NVG.  Filters intended to make cockpit lighting NVG compatible may degrade display readability and may reduce their ability to attract attention under daytime conditions.

2. The daylight readability can be assessed by flying the aircraft under bright sunlight conditions at altitudes that are representative for the aircraft type being assessed.  The altitude range should include low altitude, and the aircraft’s maximum certificated altitude, as well as at least one intermediate altitude.

3. The aircraft displays’ readability and their ability to attract attention must be assessed for various sun angles.  The sun angles should encompass the range of angles possible given the attitude limitations of the subject aircraft.  Generally direct sunlight at low sun angles have caused the greatest display readability problems.

6.2 Nighttime Readability of Cockpit Displays

This is a subjective determination of the readability of the displays under nighttime operational conditions, with and without NVG.  The displays, annunciators, and instruments are evaluated for their ability to attract attention and the presence of any shadows.  The intent of this test is to verify that night unaided flight has not been degraded by whatever modifications were required to make the aircraft compatible with NVG, and also to verify that cockpit controls, displays and instruments can be used with the pilot’s unaided field of view restricted by the NVG worn by the pilot.  An individual who is familiar with the aircraft adjusts the cockpit lighting to an operationally representative level.  The evaluator then comments on the readability of the displays, annunciators, and instruments, and the uniformity and harmony of the lighting at each crew station.  The evaluator should identify any objectionable light leaks, bright spots and reflections.  This test should be repeated with the NVG turned ON, since the NVG eyepiece brightness will require the evaluator to adjust the lighting/display brightness to higher levels to achieve adequate readability,

6.3 NVG-Aided Visual Acuity

1. NVG-aided visual acuity (VA) is assessed during NVIS compatible cockpit lighting evaluations. MIL-L-85762A specifies that a specific resolution target be placed a specific distance from the evaluator and be illuminated such that 1.6X10-10 NRB (for Class B NVG) is reflected from the white portion of the target. NVG-aided VA measurements are obtained from the evaluator seated in the cockpit with all lighting degradation in VA due to the cockpit lighting should be observed. If degradation exists, the incompatible light source(s) should be identified.

2. NVG-aided VA data are obtained using a 50% contrast United States Air Force 1951 Resolution Resolving Power Target (Tri-Bar chart) placed 20 feet from the eye point of the evaluator seated in the cockpit.  The chart consists of a large number of target elements, encompassing a wide range of sizes, divided into groups of six.  The elements progressively decrease in size (increasing in spatial frequency) at relative intervals of approximately 12%.  Each element contains two patterns, each composed of three dark lines and separating white spaces all of equal width; one pattern is horizontal and the other vertical.  Each group is identified by a different number, while the elements in each group are numbered 1 through 6.  Due to the wide range of element sizes encompassed, a series of elements, which brackets the resolution performance limit of a viewing device, may be found at any reasonable fixed viewing distance.  For a given viewing distance, the group/pattern numbers correspond to known Snellen visual acuity values (i.e. 20/20, 20/25, 20/45) varying at fixed intervals of approximately 12%.

3. Prior to the assessment of NVG-aided VA, the evaluator adjusts the NVG to obtain maximum VA.  NVG-aided VA measurements in the aircraft are obtained from an evaluator seated in the cockpit under the following conditions:

  1. Viewing forward through open air with all cockpit lighting extinguished;
     
  2. Viewing forward through the windscreen and all cockpit lighting extinguished; and
     
  3. Viewing forward through the windscreen and HUD combiner (if so equipped) with the cockpit lighting adjusted to an operationally representative level. The annunciators must all be illuminated and cause no unacceptable degradation of NVG aided VA.

4. The aircraft cockpit lighting is considered compatible if no degradation of NVG-aided VA is measured between conditions 3(b) and 3(c). Visibility through the windscreen on NVG-aided VA is assessed by comparing NVG-aided VA between conditions 3(a) and 3(b).

5. A limited amount of degradation in NVG performance, as measured by the tests described in this section, may be acceptable.  The following describes the acceptable levels of degradation in NVG-aided visual acuity (VA):

  1. The design and/or composition of transparencies may result in the loss of energy to which the NVG is sensitive, which can result in image degradation. A loss of one resolution element (approximately 12%) is acceptable. Windshield anti-ice systems may cause distortion in the area being heated. The distortion may in turn cause some degradation of the outside scene when viewing through the affected area during daytime or when using NVG. The effect should be evaluated during flight test to determine the impact to operations, and, if necessary, relevant procedures should be developed and incorporated into applicable aircraft manuals. No added degradation to resolution due to this distortion is acceptable. The evaluator should review operating limitations when testing the anti-ice system. Damage to the windshield can occur if the system is actuated inappropriately.
     
  2. A maximum loss of one resolution element (approximately 12%) is acceptable when attributed to warning, master caution and/or master warning messages/annunciators.

6. All other interior aircraft lighting shall not degrade NVG-aided VA. The combination of all degrading effects shall cause a maximum loss of no more than one resolution element.

6.4 NVIS Radiance

1. This test need only be performed if the NVG-aided VA test detects that the aircraft lighting degrades the NVG-aided VA.  MIL-L-85762A specifies that NR be measured from the cockpit displays.  NR theoretically represents the amount of energy within the spectral response range of the NVG that would be reflected by a defoliated tree under clear starlight conditions.  MIL-L-85762A establishes NR limit values to ensure that the cockpit lighting is no brighter than the outside scene during this operating condition.  NR limit values are specified in Table IX of MIL-L-85762A, and are established for Class B (NRB) NVG.  Any lighting that produces radiance greater than the appropriate specified NR value is incompatible by definition.

2. NR is measured using a NVG inspection scope (such as the Hoffman NVG-103).  The inspection scope contains an internal reference source that is adjusted to the NR limit value (1.7 x 10-10 NR as appropriate for Class B lighting systems) specified in MIL-L-85762A.  An intensified image of both the internal reference source and the scene of interest is visible in the eyepiece of the inspection scope.  The cockpit lighting is adjusted to an operationally representative level by an individual familiar with the aircraft cockpit, and then scanned by the evaluator using the inspection scope to identify any light sources appearing brighter than the internal reference source.  The radiance of any bright sources is measured.  The inspection scope is fitted with a Class B filter when scanning for bright light sources.

3. To derive NVIS radiance values, MIL-L-85762A requires that the brightness of primary and secondary displays be adjusted to produce 0.1 foot-Lambert (fL), and the brightness of monochromatic electronic and electro-optical displays be set to produce 0.5 fL.  However, during lighting evaluations the displays are adjusted to operationally representative levels that may or may not equal 0.1 fL, so their actual luminance values are measured with a photometer.  MIL-L-85762A allows a scaling factor (specified luminance divided by measured luminance) to be used to adjust the NR value to match the operationally representative luminance.  The scaling factor can influence the overall determination of NR.  For example, a measured luminance greater than the specified luminance will produce a small scaling factor.  When that scaling factor is multiplied by the measured NR, the result is a smaller overall NR value.  Luminance measurements for this evaluation are obtained using a spot photometer with a close-up lens providing a measuring field diameter of 0.5 mm at minimum focus distance.

6.5 Aircraft Mounted External Light Source Evaluation

All the aircraft’s external light sources must be assessed for objectionable glare and reflections from all crew stations under both NVG-aided and unaided night flight conditions.  If components of the aircraft, such as FLIR, landing gear, or directional spotlights, can change the external configuration of the aircraft then they should be assessed in their worst possible configuration.  The following is a partial list of external aircraft mounted light sources:

  1. Position lights;
     
  2. Anti-collision lights;
     
  3. Landing lights;
     
  4. Search lights; and
     
  5. Formation lights.

6.6 Field of View Assessment

The field of view must be assessed for operational suitability at all flight crew stations.  This must be performed under both NVG-aided and unaided night flight conditions.  As a minimum, the assessment must include the following:

  1. All manoeuvres planned for the in-flight evaluation must be briefed during the pre-flight briefing;
     
  2. Aircraft structure does not interfere with required crew movements.

6.7 Aircraft Mounted External Light Source Evaluation

All the aircraft’s external light sources must be assessed for objectionable glare and reflections from all crew stations under both NVG-aided and unaided night flight conditions.  If components of the aircraft, such as FLIR, landing gear, or directional spotlights, can change the external configuration of the aircraft then they should be assessed in their worst possible configuration.  The following is a partial list of external aircraft mounted light sources:

  1. Reflections on aircraft transparencies;
     
  2. Detection of obstacles/terrain; and
     
  3. Suitability for operational manoeuvres.

7.0 SAFETY CONSIDERATIONS

The flight test procedures proposed will result in the aircraft being flown in poor illumination conditions at night, possibly in close proximity to terrain and obstacles.  The following are proposed as means to mitigate the risk inherent to this type of flight test:

  1. All manoeuvres planned for the in-flight evaluation must be briefed during the pre-flight briefing;
     
  2. The evaluation crew must familiarize themselves with the area used to evaluate the aircraft at night.  Particular attention must be focused on the terrain, obstacles, and off-site landing area.  Suitability of area must be assessed during the day prior to flight at night. Emergency landing areas should be identified;
     
  3. Flight crew spatial awareness must be maintained at all times.  If either crew member has any doubts about the safety of the aircraft then the aircraft must be placed at a suitable altitude, in non-manoeuvring flight until the flight crew is comfortable continuing with the test program;
     
  4. Prior to commencing the test ensure that all the barometric altimeters are set to the current altimeter setting, and that the radar altimeter (if installed) is serviceable. Set an appropriate "decision height" in the radar altimeter;
     
  5. Ensure that the surrounding terrain is visible, and that obstacles can be seen and identified with the NVG.  Remain vigilant for uncharted obstructions;
     
  6. Maintain awareness of other air traffic; and
     
  7. Manoeuvres should be immediately abandoned if visual contact is lost with any obstacles or terrain during a test sequence.

8.0 OPERATIONAL APPROVAL

Commercial and Business Aviation Advisory Circular (CBAAC) No. 0251 and Commercial and Business Aviation Policy Letter No. 176 referenced in section 2.0 of this document should be consulted for operational approval and use of NVIS in helicopter operations.

9.0 CONTACT OFFICE

For more information please contact:
Policy Standards Coordinator (AARDH/P)
Phone:              613-990-8234
Facsimile:            613-996-9178
E-mail:              AARDH-P@tc.gc.ca

Suggestions for amendment to this document are invited and should be submitted via the Transport Canada Civil Aviation Issues Reporting System (CAIRS) at the following Internet address:

http://www.tc.gc.ca/eng/civilaviation/opssvs/secretariat-cairs-menu-209.htm

or by e-mail at: CAIRS_NCR@tc.gc.ca

Original signed by Gilles Morin

Chief, Regulatory Standards
Aircraft Certification Branch



Date modified: