Enhanced Vision System
An "Enhanced Vision System" (EVS), an "Enhanced Flight Vision System" (EFVS), and "Forward Looking Infrared" (FLIR) might refer to the same thing or maybe completely different, depending on what you are reading. The distinction can be important:
- The FAA thinks of EFVS as the infrared system viewed through a HUD while an EVS is viewed through a PFD. An EFVS can be used, under some conditions, to fly below published minimums. An EVS cannot.
- The European Union uses EVS to refer to what our FAA calls EFVS. (EU Ops 1, Subpart E, Section OPS 1.430)
- Gulfstream calls its EFVS an EVS, while the FLIR is simply the camera. When reading a Gulfstream manual, EVS is EFVS.
FLIR vs EVS vs EFVS, from Eddie's notes.
[G450 Aircraft Operating Manual §2A-34-90 ¶1.]
- The Enhanced Vision System (EVS) increases the ability of the pilot to see the external environment during periods of low light or reduced visibility by converting infrared radiation frequencies into visible imagery viewed on the Head Up Display (HUD). While normal human sight is limited to the 400 - 800 nanometer frequencies, the Forward Looking Infrared Receiver (FLIR) camera in the EVS detects frequencies down to the 1,300 - 4,900 nanometer range. The composite display imagery of flight guidance cues and infrared heat sources is particularly effective in low visibility approaches since the frequency range of the EVS encompasses the heat given off by runway and taxiway lighting and the higher temperature levels of the paved surfaces warmed by airplane ground operations. The EVS incorporates selective filtration to attenuate or lessen the heat bloom from runway lights and sequenced flashers, providing a more refined view of the airport environment.
- The infrared camera field of view is thirty degrees (30°) horizontally and twenty degrees (20°) vertically. Imagery captured by the camera is routed through a processor that converts the infrared picture to a raster format and communicates the formatted data to the HUD overhead unit. The overhead unit synchronizes the data with the navigational and situational symbology presented on the HUD combiner to display a congruent image with an extended visual range. The composite display imagery of flight guidance cues and infrared heat sources is particularly effective in low visibility approaches since the frequency range of the EVS encompasses the heat given off by runway and taxiway lighting and the higher temperature levels of the paved surfaces warmed by airplane ground operations. The EVS incorporates selective filtration to attenuate or lessen the heat bloom from runway lights and sequenced flashers, providing a more refined view of the airport environment.
Infrared Camera (FLIR)
[G450 Aircraft Operating Manual §2A-34-90 ¶2.B]
- The infrared camera is mounted in the nose of the airplane behind the EVS window. The installation of the camera requires careful alignment with transits and levels to focus the camera in the same line of sight as the Head Up Display (HUD) in order that the infrared image will conform to the data displayed on the HUD combiner. The camera assembly incorporates a series of lenses to focus the infrared energy received through the window onto a sensor plate. The sensor plate is composed an array of pixels arranged in a 320 X 240 format. The individual pixels are 30,000 nanometers square and detect infrared radiation. The patterns of infrared detected by the pixels are amplified and converted into electrical signals that forwarded to the system processor where they are formatted into raster images.
- The camera is enclosed within a casing that is temperature controlled by a cooling unit. The actual camera operating temperature is seventy-seven degrees Kelvin (77°K) or minus three hundred twenty-one degrees Fahrenheit (-321°F) / minus one hundred ninety-six degrees centigrade (-196°C). When the EVS system is initially selected ON, a time delay of approximately thirty (30) minutes is required for the cooling unit to reduce the temperature within the camera enclosure to operating range.
- The exterior of the camera enclosure, window hardware and processor also require cooling airflow to ensure proper operation. A duct routing conditioned air to the components provides an air supply at lower airplane operating altitudes. The valve, located in the lower cockpit supply duct, closes at eighteen thousand feet (18,000 ft) since temperatures at that flight level are low enough for ambient cooling and the EVS is not normally required above that altitude. The air supply valve is controlled by the same relay that extinguishes the landing lights.
Display Controller Menu
Figure: G450 Display Controller HUD Menu, from Eddie's aircraft.
The Display Controller HUD menu controls both the HUD and the Enhanced Vision System (EVS).
The HUD options are discussed here: G450 Heads Up Display System / Display Controller Menu. The EVS options are as follows:
[G450 Aircraft Operating Manual, §2A-34-100, figure 31.] EVS SELECTIONS ON HUD MENU:
- NUC (Non-Uniformity Correction): Selects NUC ON and OFF. Default is OFF.
- FLIR: Selects FLIR camera ON and OFF. Selecting FLIR camera OFF also selects EVS OFF (if it is ON). It may take up to 10 minutes to appear when FLIR is selected ON.
- EVS: Selects EVS ON and OFF. Selecting EVS ON also selects FLIR camera ON (if it is OFF).
- AUTO / H / L: Toggles FLIR camera through AUTO, high (H) and low (L) gain settings. Default is AUTO.
The description notwithstanding, the EVS selections are actually not to hard to difficult:
- The system does a NUC for you at certain times but you can force it to do one anytime you like by pressing this button.
- The FLIR is the camera alone. You can turn the FLIR on by itself with no EVS, but if you turn the FLIR off, the EVS isn't going to work so it will turn itself off.
- The EVS is the infrared system that gets you below minimums and it can't work without the FLIR. So if you turn on the EVS and the FLIR is off, both systems come on.
- The FLIR gain can be forced into high setting if you find the need to do so.
Non Uniformity Corrections (NUCs)
[G450 Aircraft Operating Manual §2A-34-90 ¶2.C.]
- The [EVS processor] monitors window heat states and performance, initiates camera enclosure cooling, performs camera pixel sensitivity level tests called Non Uniformity Corrections (NUCs), and initiates a Built In Test (BIT) on command of the Monitor and Warning System (MWS) at EVS start up.
- The processor controlled NUC tests are essential to maintaining a proper signal to noise ratio for the camera sensor plate. The tests correct the sensitivity of each pixel to a normal response value at a standard temperature. When the EVS is initially powered, the processor initiates an extended NUC that involves calibrating pixel response at two distinct temperature levels that requires four (4) minutes to complete. During an approach when flaps are extended past ten degrees (10°), the MWS prompts a shorter duration NUC at a single temperature level to prepare the EVS for use during landing. A NUC can be manually selected at any time with a Line Select Key (LSK) on the HUD page of the Display Controller.
Qualification to Lower Minimums
[FAA GIV-X/GV/GV-SP FSB report, ¶1.9.3.] From February 1998 to August 2001 the GV FSB Chairman participated with the FAA Los Angeles Aircraft Certification Office in EVS development, proof of concept, and certification flight tests. Those flights included over 50 EVS approaches conducted at approximately 15 different airports during day, night, Visual Meteorological Conditions (VMC) and Instrument Meteorological Conditions (IMC). Gulfstream’s GV EVS Airplane Flight Manual Supplement was evaluated and found acceptable during the certification flight tests. In September 2001 two GV FSB members received EVS ground school, simulator, and airplane training from Gulfstream Aerospace Corp. (GAC), in Savannah, GA. It was found to be operationally suitable. EVS meets the requirements of EFVS (Enhanced Flight Vision System) as defined in FAR 91.175.
[FAA GIV-X/GV/GV-SP FSB report, Appendix 7] EVS meets the requirements of EFVS (Enhanced Flight Vision System) as defined in FAR 91.175. Flight crewmembers may use EVS to meet the visibility requirements of Title 14 CFR Section 91.175 provided that vertical guidance with reference to an obstacle-free path is used.
The G450 EVS can be used to fly below published minimums under specific conditions.
[FAA GIV-X/GV/GV-SP FSB report, Appendix 7]Flight crewmember training must include a review of Title 14 CFR Section 91.175 and a review of the associated EVS AFM system description, limitations, and procedures. Flight crewmember training must be accomplished using a level 'C' simulator, with a daylight visual display, or a level 'D' simulator that has been qualified by the National Simulator Program for EVS, or the aircraft. The FSB has determined that each pilot in command of an aircraft equipped with EVS should receive a minimum of 4 hours of ground school training followed by a minimum of 2 hours of simulator training in the left seat of a level 'C', with a daylight visual display, or level 'D' simulator. An EVS equipped aircraft may also be used in lieu of a simulator for training. In-flight training should consist of a minimum of 2 hours of flying in the left seat of the EVS equipped aircraft. The flight portion of the training should consist of a minimum of two (2) day and two (2) night approaches each with vertical guidance.
Checking requires a proficiency check conducted in a level 'C' simulator, with a daylight visual display, in a level 'D' simulator, that has been qualified by the National Simulator Program for EVS, or on an EVS equipped aircraft. The proficiency check will include at least one instrument approach to published minimums and landing utilizing the EVS. This check can be accomplished concurrently with a proficiency or competency check under 61.57, 61.58, 121.441, 135.293, or 135.297. Currency: If 61.57 (c) is being used for currency, at least one of the 6 required instrument approaches must be accomplished using EVS to published minimums.
EVS Window and Heating Controls
[G450 Aircraft Operating Manual §2A-34-90 ¶2.A.] The EVS window is manufactured from one quarter inch thick synthetically grown sapphire is highly transparent to infrared thermal frequencies, allowing 98% transmissivity to airfield and approach lighting systems. The window is mounted in an aluminum frame beneath the radome and incorporates a grid of resistive metallic elements and three thermostats. The window is heated to a temperature between 12° - 14°C to prevent the formation of ice and to ensure uniform radiation transparency.
[G450 Aircraft Operating Manual §2A-34-90 ¶2.B.] The camera is enclosed within a casing that is temperature controlled by a cooling unit. The actual camera operating temperature is -321°F. When the EVS system is initially selected ON, a time delay of approximately 30 minutes is required for the cooling unit to reduce the temperature within the camera enclosure to operating range.
EVS II Power On Operation
[G450 Aircraft Operating Manual §2A-34-100 ¶2.A.] When power is applied to the EVS II system and the airplane is on the ground, a Power-up BIT (PBIT) is performed, taking 15 seconds. When power is applied in the air, the EVS II skips the Power-up BIT and completes initialization within 5 seconds. Then an automatic Built-In-Test (BIT) sequence is initiated; all system functions are checked. The BIT takes approximately 1 minute. When initially powered, the EVS II FLIR may take up to 15 minutes to cool its detector to operating temperature and activate for an initial power-on. If the EVS has been previously activated, this activation period may be shorter depending on the deviation from nominal operating conditions that has occurred since power-off. When the aircraft is parked overnight in temperatures below -40°C, the EVS II FLIR may take up to 35 minutes to heat the electronics to operating temperature and to cool the detector to operating temperature. Once the FLIR is cooled to temperature, the EVS II will perform a NUC and then enable video to be displayed on the HUD. The NUC completes its cycle within 1 minute.
EVS II Failure to Power-up
Enhanced Vision System (EVS) II have been experiencing a nuisance failure upon application of electrical power. The symptoms of the condition are the amber EVS Fail (A) and blue EVS Maintenance Required (B) Crew Alerting System (CAS) messages, accompanied by the Central Maintenance Computer (CMC) Active Maintenance Message "FLIR Rx Fiber Fault". After cycling power as described below, the system behaves normally.
- Ensure EVS is commanded ON (not STANDBY) (Display Controller Head-Up Display [HUD] Menu) then pull Forward-Looking Infra-Red (FLIR) camera and processor Circuit Breakers (CBs) for one second (pilot's overhead CB panel).
- Close FLIR CB then the processor CB.
- Allow up to 15 minutes (most likely around 10 minutes) for FLIR to cool and video to be valid before selecting EVS on the HUD.
The operator may choose to view EVS temperatures on the CMC screen during the FLIR cool down to check that FLIR-to-processor communications are working. If the FLIR temperature is 127 degrees Celsius or higher, FLIR-to-processor communications are not operating properly. If valid temperatures are displayed, FLIR-to-processor communications are functioning normally.
EVS II Limitations
[G450 Aircraft Operating Manual §2A-34-100 ¶5]
- The HUD or HUD II section of the G450 Operating Manual must be immediately available to the flight crew whenever use of the EVS system is contemplated.
- At 100 feet HAT, visual cues must be seen without the aid of EVS or EVS II to continue descent to landing.
- EVS may be used only by qualified pilots who have been trained in accordance with requirements listed in the FAA G450 Flight Standardization Board (FSB).
- Flight Director or autopilot with vertical guidance is permitted for all IMC EVS approaches.
- EVS, as installed, meets the requirements of EFVS (Enhanced Flight Vision System) as defined in 14 CFR Part 91.175.
EASA Air Ops Annex 1 to VIII, European Aviation Safety Agency, 09 May 2017
Gulfstream G450 Aircraft Operating Manual, Revision 35, April 30, 2013.