Flying Police Helicopters on NVGs
Of all the tools and equipment in use today in law enforcement aviation few things compare to the night vision goggle for enhancing mission capabilities and safety. The use of NVGs while flying is a fairly straightforward concept. Fly into San Diego's back country (or any mountainous region) unaided and you are flying into a black hole. Now simply flip down the set of night vision goggles attached to the front of your helmet and like magic you now see the mountain in front of you that you might have otherwise flown into.
Night vision goggle technology was first developed for military use, and came about during World War II. However it was not until the early 70s that NVG technology began to be adapted for military aviation, primarily by the U.S. Army. Almost all of what we know today about flying helicopters on NVGs can be attributed to the U.S. Military. In fact our unit policies and practices regarding NVG flight were taken right out of the U.S. Army's flight manuals.
Developing a program to fly helicopters on night vision goggles was in no way a simple or easy transition. Many military aviators paid with their lives as they discovered what worked and what didn't. Though the concept of flying on NVGs is straightforward, see the mountain or don't see the mountain, the act of operating a helicopter on NVGs, in low level flight, in mountainous terrain is not at all simple or easy. Night vision goggles do on one hand expand your mission capabilities, but on the other hand bring a whole new set of limitations, along with an entire new skill level that must be learned.
How do they work: While this is not a technical article on NVGs let's take a quick look at what they really are, and how they work. The NVGs that we use are known as ANVIS models, which stands for Aviators Night Vision Imaging System. Our night vision goggles come off of the exact same assembly line as the goggles presently used by our military helicopter pilots.
NVGs do not magnify the view in any way as does a set of binoculars. Magnifying the view would really cause problems for the pilot trying to maintain situational awareness. NVGs detect ambient light and amplify it many thousands of times. Light is light regardless of the source. Whether it is star light, moon light, city lights, flashlights, or spotlights, the goggles pick up the light and amplify it through image intensifier tubes, projecting the image onto a monochromatic green phosphor screen. Green is used because the human eye is most sensitive to the color green. The pilot is not actually looking through the goggles as you would a set of binoculars. The pilot is actually watching two small screens, similar to TV screens in front of his eyes. From the pilot's point of view however, it appears as though you are looking right through the tubes at the scene in front of you.
The night vision goggles we wear are powered by nothing more than two AA batteries worn in a battery pack on the back of the helmet. The pack actually contains 4 AA batteries but two are back up batteries. As one set of batteries begins to run low, the pilot or TFO will get a signal via a tiny red light within his or her field of view. The pilot then has plenty of time to reach up to the back of his helmet and flip the switch from one set of batteries to the other. We often joke that we fly million dollar police helicopters on two AA batteries, but that is exactly what we do.
Limitations of NVGs: So if night vision goggles allow you to see into the night, why then do we say that they come with an entire new set of limitations? Isn't it just that much easier to fly around at night with goggles? The answer is both yes and no. The goggles have limitations that the natural eye does not. Flying on goggles gives you reduced visual acuity, reduced contrast, reduced depth perception, greater visual fatigue, and most goggles limit your view to 40 degrees (40 degree field of view or FOV).
Knowing how the goggles are actually worn and used, will help to understand how we deal with the limitations of the goggles. First the goggles are adjusted to a position approximately one inch in front of the eyes. This gives the person wearing the goggles unaided peripheral vision as well as the ability to look underneath the goggles with direct vision. To read the instrument panel or to perform other cockpit functions the pilot or tactical flight officer simply looks underneath the goggles just as you can look underneath a set of sunglasses or reading glasses. We use NVG friendly lighting in the cockpit after dark to allow reading of the instruments with unaided vision.
Flying a police helicopter over the city at night time does not require night vision goggles for safe operation. However, many police pilots will continue to wear goggles over city lights for a variety of reasons. It still enhances mission safety and capability by allowing you to see things you might not otherwise see, but it also gives you distinct advantages over the bad guys who like to use darkness as cover while they go about their criminal enterprise. Oh and some of our cities out here in California still have mountains in the middle of them.
Back to the goggles and their limitations. So flying over city lights at night, on goggles, the pilot is still picking up all of the city lights with his or her unaided peripheral vision, providing more complete situational awareness. To put it in simpler terms, as I see the city lights moving past me in my peripheral vision, I still have my sense of movement, and direction. I can still get a strong sense of how fast I am flying (without looking at the flight instruments) and whether I am climbing or descending. All of these are extremely important visual cues our brains depend on in order to operate the helicopter safely.
Now let's take the same helicopter and crew and put them over mountainous terrain, with a very bright full moon directly overhead, but zero city lights. The mission has definitely become more difficult, as there are not as many visual cues coming in from the peripheral vision. Because of the full moon however, it is so bright that you can see the shadow of the helicopter moving along the ground beneath you when viewed on goggles. Because of the less visual cues and the 40 degree FOV the pilot must move his head more in order to get the same sense of movement and situational awareness.
Now, same crew and police helicopter, but zero moon, zero city lights and you need to fly into a dark canyon in the back country and pick up a couple of cold, wet, lost hikers one of which is a small child. (Think it doesn't happen, during my initial NVG training we picked up 5 cold wet hikers, 4 of which were children with the youngest being only about 8 years old. The senior pilot/NVG trainer flew that mission while I performed the TFO duties.) Yes we have night vision goggles that amplify the ambient light thousands of times, but this is a much more difficult mission. One that requires significant training, as well as a tremendous amount of mental focus. This is without question where the goggles enhances your mission capabilities, but only so far as you properly manage all of the goggle's limitations. Remember the reduced visual acuity, reduced contrast, reduced depth perception, 40 degree FOV, and visual fatigue. This is when it all comes into play.
For a mission such as this you would generally fly to the area and hope to locate the victims with some type of light source. Even a tiny pen light or a match carried by the lost hiker can easily and quickly pinpoint their position to a helicopter crew wearing NVGs. Once the subjects are located you would recon the area for a possible LZ, knowing that on a dark night you may not know if there is a suitable LZ until you get down into the area and look for one. This is going to require an approach to a hover, then the crew can search for a suitable LZ from a hover.
The approach to an off field, unimproved LZ on goggles is performed "painfully slow." This requires excellent crew coordination, checking for obstacles throughout the approach. Because of the reduced visual acuity, contrast, etc., the pilot must constantly move his head back and forth picking up visual cues to the helicopter's movement by looking out to the side. Once the helicopter and crew are in a hover, they can set about choosing a suitable LZ, with the TFO helping to keep the helicopter and tail rotor clear of obstacles.
During the entire process the pilot will be managing all of the lighting on the police helicopter to his or her benefit. Once low level in a dark environment, the Anti-Collision strobe is often turned off as it can be very distracting to the point of being dangerous. Helicopter position lights can be left on or turned off. On our MD530F helicopters the position lights are mounted on the very front of the skids. The red position light on the pilot's side throws off an enormous amount of light once it is amplified by night vision goggles. Sometimes this light is helpful sometimes it isn't. Every mission and location is different. Once in a hover the pilot can use his landing light, and or belly light to light up the area and assist checking for obstacles and LZs. Use of the belly light or landing light in a hover allows the pilot to transition to unaided vision by looking under the goggles if preferred, or gain back some of his peripheral vision if he chooses to continue using NVGs.
There are many aspects of flying helicopters on night vision goggles that this article will not address. In many ways I have only scratched the surface. How does the brain compensate for reduced depth perception? There are night illusions while flying on NVGs that a pilot must be aware of if he or she wishes not to become a statistic. There are some missions that just can't be performed even with NVGs, due to lighting, location, and other environmental factors.
Though originally developed for military use, there are a multitude of civilians who have been plucked out of cold, wet, dark and treacherous locations thanks to night vision goggle technology.
Night Vision Goggles and crime fighting: When it comes to simply chasing and catching bad guys the night vision goggle is bit like having a pair of those x-ray glasses you used to see advertised when you were a kid. Only the NVGs actually work. Ok, you can't see through clothing, or through walls, or into people's houses, but you can see into dark corners, and fields, and yards and other places where the criminal element often lurks at night.
Without giving away all of our secrets I will tell you that it is quite difficult for a person on foot to outrun a helicopter, a spotlight and two pair of NVGs, (pilot & TFO). Of course NVGs are not the only tools we have on board for locating or catching wanted subjects. The FLIR or Forward Looking Infrared camera senses heat or heat differential in objects within it's view. You can see then that NVGs and FLIR cameras work on completely different principles, but often seek to perform the same mission only by different means, at least when it comes to locating wanted subjects.
Most often while the Tactical Flight Officers is performing a FLIR search, the pilot is watching the flir screen with his unaided vision, watching the scene below (where the TFO is searching) on goggles, while never forgetting that his or her first and primary function is the safe operation of the police helicopter. Even with NVG and FLIR capabilities the criminal suspect is not always caught. Any cop or crook could tell you that. But compared to the early years of police aviation where all a police helicopter crew would have is a spotlight and the naked eye, the NVGs coupled with the FLIR make it much more difficult for the criminal suspect to elude capture.
Night vision goggle technology is now a permanent and essential part of law enforcement aviation.