Learning To Fly with Night-vision Goggles

A variety of companies offer pilots training to fly with night-vision goggles (NVG), but one is also the pioneer of developing NVG for the civil aviation market and manufactures and maintains these precision optical-electronic devices: Aviation Specialties Unlimited (ASU). AIN visited ASU recently at its Boise, Idaho headquarters to learn more about NVG, including participating in a training class and flying ASU’s Bell 505 at night while wearing NVG.

NVG have seen dramatic improvements since military helicopter pilots first began flying with them in the 1960s. Now most medevac operations use NVG during night operations, and they are penetrating the fixed-wing market, such as for night agricultural flying and other types of operations with minimal ambient lighting. ASU offers training in its Bell 505 and a Cessna 206 equipped for NVG operations and says it is the only company offering fixed-wing NVG training. ASU also certifies and installs the required NVG-compatible lighting and avionics filters on airplanes and helicopters.

Early NVG were much lower resolution, heavier, and subject to more anomalous image artifacts that made using them difficult. NVG amplify existing light by 6,000 to 10,000 times, a great aid for pilots flying in areas with little natural or artificial lighting. The technology involved has improved greatly, and ASU is now employing the latest version of the image intensifier “tube,” the component that amplifies the light, in its lightest and most compact set of NVG, the E3. 

A simple description of a set of NVG would describe it as two lenses surrounding an image intensifier, and there are two of these components, one for each eye. Just because they are binocular, however, doesn’t mean that NVG provide a binocular view, like wearing glasses, for example. The view is monocular, which does affect depth perception, but there are techniques to overcome this, and I didn’t find it difficult. The sight picture through each goggle is limited to a 40-degree field of view, which means the pilot must look around to get a complete view of the outside world.

The image intensifier tube, which is only about half an inch long, is where the magnification happens. As light enters the tube, a photocathode converts light energy (photons) into electrical energy (electrons), as ASU describes the process.

The key component of the tube is the microchannel plate, a thin wafer with more than 10 million hollow fiber-optic channels. As the electrons move through the microchannel plate, they encounter passages coated with a special material and tilted at 5 to 8 degrees. This causes the electrons to multiply dramatically, thus providing the massive amplification. The electrons then pass through a phosphor screen, and this converts them back into photons, which then pass through a fiber-optic inverter consisting of light-transmitting fibers twisted 180 degrees to ensure proper orientation of the image.

All of this requires energy, and surprisingly just 3 volts from two AA batteries are sufficient for up to around 50 hours of operation. The power supply, an even more complicated device inside the tube, converts the 3 volts to the voltage required by each component. One of the functions of the power supply is autogating, automatically adjusting the voltage sent to the microchannel plate to manage brightness when looking at low-light conditions that suddenly change to bright light. “The image gets brighter and then, after a momentary delay, suddenly dims slightly to a constant level,” according to ASU.

ASU’s NVG Program

Joseph Estrera, president of ASU, is a scientist deeply involved in the design and construction of NVG, including their image intensifiers. He spent more than 20 years at L-3 Electro-Optical Systems, eventually becoming chief technology officer (CTO) of its Warrior Systems division, developing these products and deploying them into the military. “Ultimately, I decided I wanted to go back and do aviation night vision,” he said. “And then I ended up at ASU 10 years ago, and I became the CTO and the new product development head.” Now, he is focused on productionizing the E3 NVG. 

One of the challenges in designing the E3 system, according to Estrera, is that “the higher the weight of the optic, the more powerful the optic is.” ASU founder and former AH-64 Apache pilot Mike Atwood had challenged Estrera to make a new goggle system that wasn’t like a typical Russian system—effective but heavy. 

“Now the way you beat it is you have to innovate the optic,” Estrera said, “and if you make the optic lighter, you cannot lose visual acuity or the ability to have powerful optics that can see objects at long distances. So we had to develop an optic that beat the weight but kept the same performance, and that's part of how we innovated this goggle system.”

Cutting 170 grams was challenging, but ultimately achievable, and this enabled removal of counterweights that balanced the load on the front of the helmet. “When you look at this correctly,” he explained, “you need to put this four to five inches or longer from the actual base of the human head. And then you really feel the physical weight of this [device]. So this is what you're exposing the human neck and the human body to in a continuous mode because they're using these goggles for hours. And some are doing it for days and months.

"It's just a matter of time before this starts breaking the tissue in the back of your neck. That's what happens with a lot of pilots. They tend to have bad orthopedic problems in their spine and their neck over time. I'm not a pilot, but when you talk to pilots, that's one of their first complaints, which is why I wanted to build this device. But the disparity is it cannot be heavy and it cannot be a non-ergonomic feel and use of a system. That's what Mike Atwood was complaining about: not Russians in general, [but] the fact that it was heavy and not easy to use. And that's why I built this goggle, for that very purpose.”

Training Plan

ASU's NVG training includes a full day of ground school followed by three nights of flight training, either in the Bell 505 or Cessna 206. ASU also offers training at customer locations and will train personnel for companies wanting to start their own NVG training program, sell them goggles, and provide the required periodic NVG maintenance.

Our class included me plus two fixed-wing pilots whose company planned to expand its capabilities with NVG, and they would be flying in the 206. ASU chief flight instructor Bradley Brummett led the ground school and also teaches fixed-wing flying. Because it was early summer in Idaho, our night flying would have to wait until official darkness after 10 p.m. Afternoon naps were highly recommended.

During the ground school, we learned some NVG history; the technology of the tube; ASU’s founding in 1995 by Atwood and its growth as a developer of NVG, repair station, engineering center for NVG supplemental type certificates, and training provider; the regulatory framework surrounding NVG use; and instructions on how to mount NVG on a helmet and adjust the lenses. Brummett also delved into eye anatomy, day and night vision and constraints, how NVG can effectively make up for night-vision drawbacks, and NVG myths.

One myth, he pointed out, is that visual acuity, the ability to recognize details, is poor with NVG. In fact, while visual acuity at night drops to 20/200 “unaided”—that is, without NVG—most acuity is restored with NVG, bringing it back to 20/25.

Another myth says that there is no peripheral vision with NVG, which is true if the user is looking only through the goggles. But new NVG users soon learn that it’s easy to turn the head to look elsewhere and that looking under or beside the goggles with unaided vision is not only possible but necessary for viewing instruments and avionics or looking outside through a helicopter’s chin bubbles.

A third myth is that bright lights will “blow out” the NVG and make it difficult for the user to recover from the blast of light. The power supply’s “autogating” automatic voltage adjustment prevents that from happening.

Many believe that it’s impossible to see powerlines with NVG, but sometimes they’re visible when moonlight or the helicopter’s searchlight illuminates the wires, and with goggles, it’s usually possible to see the towers to which lines are attached. “Always assume wires are strung across valleys and ravines,” ASU advises.

It’s possible to see clouds and fog with goggles, but pilots may need to look under the goggles with unaided vision to see clouds and prevent an inadvertent IMC encounter.

Depth perception is affected because of the monocular view, but this can be overcome when looking at something close and another element further away. The flatter the terrain contour, the more difficult this can be, especially over water, which is why a radar altimeter is required for NVG operations.

An entire chapter in the ASU NVG Ground Training Guide covers terrain interpretation, and this is a topic that pilots need to study and that is covered during the three nights of flight training.

There are constraints that affect flying with NVG, as well as techniques to overcome them. 

The NVG could have visual deficiencies, and pilots need to check for these before flying. Deficiencies that make the NVG unacceptable for flight include shading that intrudes into the circle that should be visible through each monocular; edge glow, a bright or sparkling area in the outer portion of the viewing area; and flashing, flickering, or intermittent operation. Some blemishes are acceptable at a low level but may require repair of the NVG if they get worse. 

Brummett explained the regulations that cover NVG-compatible installations and operations. Basically, for an aircraft to be NVG-compatible, its internal and external lighting must “not adversely affect the operation of the NVG during any phase of the NVIS [night vision imaging system] operation.”

This involves installing NVG-compatible LED lighting and filters over avionics displays, but none of this is allowed to change required colors, for example, on caution and warning lights. The internal lighting must also be adequately viewable unaided because a pilot needs to be able to look at instruments from under the NVG or with the NVG flipped up. Tablet apps like ForeFlight work well with NVG since it’s easy to dial down the screen brightness to view the app unaided without adding too much light in the cockpit. External lighting still has to do its job of helping with detection and separation by other aircraft. As mentioned, NVG-compatible aircraft must also be equipped with a radar altimeter.

FAA regulations require that pilots have 15 hours of time in type before flying NVG. Currency requirements include three hours NVG flying over a rolling 12-week period, but only half that as pilot flying, with three takeoffs and landings, two landings off-airport including one to an unlit area and one to a confined/semi-confined area, and three hovering tasks. Pilots and crew must complete annual checks. Equipment must be maintained in accordance with the NVG manufacturer’s requirements. Flight simulators can also be used for pilot training.

There is also a training requirement for additional personnel, who are not pilots but flight crew that wear NVG and can help monitor takeoffs and landings at unimproved sites. This could be a flight nurse on an aeromedical flight, for example.

Flying with NVG

The standard set of NVG since 1998 has been the ANVIS-9 system, which originally had green phosphor imagery. Recent ANVIS-9 and the E3 NVG are equipped with white phosphor tubes, and this has proven to work better because the eyes use day or bright light photoptic vision when viewing imagery in the NVG. A major advantage of the E3 goggles is that they weigh much less than ANVIS-9 and don’t require the addition of balance weights below the battery pack to even out the load on the helmet. This is a huge benefit for pilots who fly with NVG-equipped helmets for hours at a time.

We practiced mounting, flip-up, and flip-down procedures using the lock release with the NVG on our helmets and how to switch between the primary and backup AA batteries. Adjustments included eye span so each monocular is properly aligned with each eye, fore-aft, and tilt. These helped ensure each monocular was providing the full 40-degree field of view, which should look like a complete circle with a crisp, distinct edge.

I showed up for the Bell 505 flight at 9 p.m., and it was still light out. Once it was darker, Bell 505 instructor and ASU director of operations Tony Tsantles showed me how to adjust each monocular’s lenses for optimal viewing. I switched on the goggles and looked at a high-contrast lighted feature across the airport and adjusted each objective lens first, then each eyepiece lens, to get the sharpest image. 

Tsantles taught in Mike-model Sikorsky Black Hawks in the U.S. Army and now does all the helicopter flight training for ASU customers in the Bell 505. He wore the E3 goggles during our flight while I wore the ANVIS-9s, but then we swapped mid-flight so I could see and feel the difference.

While the E3 uses the same tube as the ANVIS-9, a big difference, other than the lighter weight, is that the E3 NVG doesn’t have a metal ring around the eyepiece lens. This results in a better view through the lenses but also a cleaner unaided view because it opens up some space around the eyepiece and makes it easier to look around, not through, the lens. “The sight picture you get is much better,” he said, “but the light weight is significant.” 

After official night, which is an hour after sunset, I climbed into the right seat of the 505 with Tsantles flying left seat. We flipped our goggles into position and started the engine, and then he did the liftoff from the ASU ramp at Boise Air Terminal. Once airborne, Tsantles handed over control, and I flew the 505 over to the assault strip, an unlit runway used for military training for the Idaho Air National Guard wing.

I flew a normal approach then landed on the strip, and even with the goggles on, I didn’t feel like depth perception was compromised. There was plenty of ambient light, but I looked through the goggles almost exclusively and felt like I could easily judge the helicopter’s height near the ground. We did use the 505’s searchlight and landing light to illuminate the ground, and this proved helpful, especially when peeking under the goggles to look through the chin bubbles.

After taking off from the assault strip, Tsantles had me fly south to a low set of hills. Here he asked me to land in a small area at the top of one of the hills next to some old railroad tracks. I was able to touch down fairly precisely, not too bad given that I didn’t have much time in 505s before this, and had never flown one at night. After landing, he asked me to flip my goggles up, and it was almost completely pitch black, with one dim light visible on a hill in the distance. With the goggles on, I could see every divot in the dirt and each blade of grass dancing in the wind from the rotors. 

After taking off, I followed a draw to the north and over Lucky Peak Reservoir to a Forest Service helipad, where again I landed in what was pitch-black conditions without the goggles. There was no moonlight that night. 

After taking off from the pad, Tsantles took the controls briefly so I could see what a dying campfire looked like with goggles on and off. Without the goggles, I couldn’t see anything but with the goggles on, the small fire bloomed into view, only blocked when some trees obscured it as we flew circles over the spot. Tsantles told me about a customer who had been flying just two weeks with NVG and found a lost hiker by spotting their flip phone screen from 8 miles away. The amount of light amplification with the goggles is stunning.

We swapped our goggles so I could feel the lighter-weight E3 setup, and it does indeed add less pressure on the neck. I was fairly comfortable with the view through the ANVIS-9 goggles by then, but the E3 monoculars are easier to look around for unaided views and, although more expensive, would definitely be my choice.

Tsantles did the next landing near Little Grouse Creek, where we were surrounded by high terrain with no apparent ambient light but plenty of illumination in the NVG. I then flew us over the hills and downtown Boise and the capitol and back to the airport for a landing on the ASU ramp. I took advantage again of the 505’s generous chin bubbles to look at the ground briefly during the landing, although it was easier to hover the helicopter steadily by looking in the distance using the NVG. My touchdown was only a little bit firm.

The plan wasn’t for me to go through the full flight training portion of the ASU program, but flying the 505 with NVG gave me an excellent feel for what it’s like. I did return the following night to sit in the back seat of the 206 while one of my ground school classmates flew his second lesson. For this operation, I chose not to wear a helmet but just held the monoculars to my eyes when I wanted to get a view through the NVG so I could more easily compare the NVG versus non-NVG views and take photos and videos through the goggles.

For this flight, which again was a moonless but clear night, Brummett had the goggle-wearing student fly some steep turns for handling familiarity before heading to Ontario Airport for takeoffs and landings. As we neared the airport, Brummett—who did all the radio work—reported our position, then asked local pilots not to switch on the radio-controlled lights so the student could land at an unlit airport using the goggles. We did two landings there, then flew to nearby Weiser Airport for some more dark-airport landings. From Weiser, we flew southeast, looking at various lighted elements on the ground like cars on the freeway, flashing police car lights, transmission towers, and mountain ridges. The next stop was at Emmett, where the airport is bracketed on one side with high terrain. After two no-light landings there, we headed back to Boise.

It was interesting to look at the features along the way, and the airports, with and without the goggles. As Brummett had explained during ground school, there are some obstacles lit with LED lights that are barely visible with the NVG. In this case, it’s important to look at the base of the obstacle and use that to try to judge distance. Sometimes lights seen through the goggles look much closer than with no goggles. Looking at the airports where we were landing without the goggles held to my eyes was slightly disconcerting, but a quick move to look through the goggles brought the world back into view.

Flying with NVG was an amazing experience; so little ambient light was needed to provide a clear view through the goggles. Looking up into the night sky with the goggles reminded me of visiting a planetarium as a school kid; every scrap of the sky was filled with bright stars. However, the main takeaway from this experience is that night operations of any kind can be flown much more safely with NVG. I can’t imagine flying medevac missions to unlit areas without goggles, and the high takeup rate of aeromedical operators using NVG underscores that sentiment.