Dancing in the Dark
Night vision goggles can save a pilot’s life or, if he hasn’t had adequate training, take it.
"YOU READY FOR THIS?" THE EARPHONES INSIDE MY HELMET CRACKLED. It was a cold, moonless night over Texas and I was at 1,200 feet in a jet-black Bell 407 helicopter with Scott Baxter, an instructor with the Fort Worth-based Bell Helicopter Training Academy. From the left seat Baxter was teaching me the finer points of flying with night vision goggles, and it was time to demonstrate their usefulness during one of the more hair-raising events one can experience in a helicopter: autorotation after a simulated engine failure.
Well, was I ready? I had come to Bell's training facility to sample the thrills and chills of flying with night vision goggles. Bell's school is one of only two approved to teach civilian pilots like me how to fly with NVGs. I also wanted to learn why, over the past three decades, pilots have both praised and cursed the devices.
But I didn't come to drop like a rock into the Texas scrub. Fortunately, Baxter had 1,500 hours of NVG time, much of it in situations much more demanding than this, so I nodded: Ready. Simulating engine failure, Baxter chopped the power and the bottom fell out.
There's an old adage instructors use when they teach night flying: If you lose your engine, switch on your landing light and turn toward an area that's dark—presumably there are no houses there. If you don't like what you see when the ground comes into view, turn the light off. There's truth in the dark humor: You can't see the touchdown area with the landing light until you're about 100 feet above the ground, too late to change course very much and almost too late to halt an unpowered helicopter's steep descent.
Baxter planned to show me how NVGs change the equation. But to drive home his point, he wanted me to experience autorotation the old-fashioned way: with the unaided eyeball. So as we plummeted toward a landing at about 2,000 feet per minute, my job was to scour the depths until the landing light revealed whatever we'd be landing on. For an autorotation, you first drop rapidly, so airflow through the rotor disc increases rotor speed, then you convert the rotational energy to lift by pulling up on the collective control to increase the pitch of the blades. Finally, at just the right height above touchdown, you flare—pull the helicopter's nose up with the cyclic control. Start too low and too late and you hit the ground hard. Start too high and too early and you run out of rotor blade energy and hit harder.
Having flown with the NVGs on for only 20 minutes, I already missed them: I couldn't see anything. What looks like black emptiness to the naked eye is revealed in startlingly bright detail with NVGs. Earlier, Baxter had flown over a dark patch at 1,200 feet and had me view what looked like a large puddle of ink, possibly a good spot for an emergency landing. After clicking my NVGs into place, I could see that the ink was actually a lake with a bridge running across it. And there were fine ripples on the surface of the water, indicating wind direction.
I could see the lake, bridge, and ripples because the NVGs extended my visibility range from 690 nanometers, the high end for the human eye, to about 930, which is in the near-infrared region of the electromagnetic spectrum. A broader range renders visible objects illuminated by scattered light from natural sources—starlight, chemical reactions in the upper atmosphere, and auroras, for example—as well as objects lit by artificial sources, like city lights, headlights, fires, and flares.
The moment of enlightenment comes when you look into the darkness with NVGs and see a circular 40-degree emerald-green field of view in which night becomes not quite day but something like twilight. Though Baxter calls it "looking through a toilet paper roll," the view is quite engaging, despite the bulk of a flight helmet with an additional 1.2 pounds of hardware hanging off the front.
Before we cranked up the Bell 407, we preflighted our NVGs, adjusting the independent horizontal and vertical alignments of each tube, testing the electrical connections to the battery pack, and focusing the goggles on light sources and other objects in the waning twilight outside Bell's Fort Worth facility. We took off and buzzed along a river, through some fields and up and over a line of trees, a treacherous route made less stressful by the goggles and by Baxter's knowledge of the area. The pulse-pumping surreal experience made it clear to me that NVGs can lead, or, like a siren's song, lead astray.
"People think they're Superman," says Joe Roberts, chief of the flight instruction branch for the U.S. Army at Fort Rucker, Alabama. "It's like watching TV—the obstacles going by the airplane don't seem real like they do in the daytime." Roberts says this kind of illusion is one good reason why Army warrant officers get an initial 30 hours of NVG training at Fort Rucker, plus an "absolute minimum" of another 10 hours when they get assigned to units in the field.
Education is the tool of choice to counter the Superman syndrome, both in the armed forces and at Bell. The company's week-long NVG course, created by Baxter and C. "Mac" McMillian, Bell's chief flight instructor, demonstrates to students in the civilian sector both the advantages and the limitations of NVGs. Pilots can take the $8,500 package, which includes six lectures in the classroom and at least 7.5 hours in the air at night in the school's three NVG-equipped helicopters, before they take jobs with police or emergency medical services (EMS) operations. Baxter briefed me on the schoolwork before we flew, describing classroom modules on everything from cockpit lighting to mission planning.
Information in Bell's course is largely drawn from the harsh lessons that the military, particularly the Army, learned when it first put NVGs into aircraft in the 1970s. "They gave them to us and said, ‘Go fly,' " says Roger Anderson, a former Army helicopter pilot who is now a marketing manager with NVG maker ITT Industries.
While archaic by today's standards, the first aviation goggles, called PVS-5s, were quite advanced compared to the IC-16 infrared night scopes, known as Gen 0 (generation zero) technology, that appeared in the field in the 1950s in order to gain the tactical advantages of being able to see an enemy who couldn't see you. Since that time, night vision systems took two paths: Infrared sensors like the IC-16 evolved into forward-looking infrared (FLIR) systems, which include a bulky sensor pod outside the aircraft and an electronics box and display unit inside, while goggles evolved into image intensifiers. FLIRs, while well suited to view details of a target area from a head-up or panel-mounted display, are not good candidates for piloting, partly because the view doesn't follow the pilot's line of sight.
In Vietnam in the 1960s, ground forces used unwieldy Gen 1 image intensifiers called starlight scopes, in which three image intensifier tubes were stacked end to end, like flashlight batteries. Gen 2 came out in the 1970s with the introduction of the microchannel plate, which eliminated the need to stack multiple intensifiers and paved the way for compact helmet-mounted goggles like the PVS-5.
While the technology had improved, inexperience with human factors issues in night vision systems for aviation proved troublesome and often disastrous. Unlike today's NVGs, the PVS-5 clamped onto the pilot's face like a weighty scuba mask. In order to see the instrument panel, crews had to either focus one side of the goggle outside and the other on the instrument panel, or have one pilot focus outside and one inside.
Dutch Fridd, an EMS pilot and the first civilian appointed as an NVG instructor by the Federal Aviation Administration in 1999, began using the full-face PVS-5 in 1978 in Army helicopters. Fridd says crews went out with no guidance on the use of the goggles and no information about their performance in various weather conditions. Some pilots were refusing to fly and others who tried had trouble controlling their helicopters or became ill from spatial disorientation. "During formation takeoffs, you had people flying backwards, sideways," Fridd says. "Others were hitting wires or trees." During his first 40 or 50 hours of PVS-5 flight time, he "absolutely detested it," he says.
But the pilots felt that they had to make it work: "The only way we'd survive [in hostile airspace] would be down in the trees, and we needed goggles to do that," Fridd says. A major threat for helicopters then, as now, was shoulder-launched missiles. Anderson says the PVS-5, though not designed for aviation, gave the Army a real edge. "It didn't take long for the strategists to figure out that we'd have a huge advantage working at night," he says.
Both Fridd and ITT's Anderson say pilots eventually discovered that cutting away some of the casing below the PVS-5 eyepiece would give them a much more comfortable view both outside and inside the cockpit, a finding that was later built into Gen 3 units, which sit an inch or so away from the eye. Also problematic at the time were instrument panel lights that swamped the NVGs with photons, making it hard to see the outside scene. Pilots dealt with the problem by turning off the instrument lights and illuminating the panel with chemical light sticks—"chemsticks," which emitted light in a narrow part of the spectrum. Today's NVG-compatible aircraft emit light in the blue end of the visible spectrum or have glass filters to cancel out the white lighting of older cockpits.
In 1980, Operation Eagle Claw, the attempt to rescue 53 U.S. hostages in Iran, proved disastrous when an RH-53 helicopter collided with an EC-130 refueling aircraft, killing eight soldiers. The mission had been planned as a night operation, but pilots had received only 15 hours of NVG training, and instrument panels had to be taped over to prevent interference with the PVS-5s. As is often the case, disaster spawned research.
Gen 3 NVGs, which introduced image-enhancing gallium arsenide photocathodes, longer life (10,000 hours, up from 2,000), and other enhancements, came into service in the early 1980s and, when combined with experience gained in training and in designing compatible lighting, proved themselves in night operations in the 1991 and current Iraq conflicts. Almost every U.S. military aircraft is now equipped with compatible lighting, and crews are training to use NVGs for every night flight. Goggles continue to improve, though the technology is still called Gen 3.
Widespread use in the military has slowly begun driving NVG devices into civilian aviation; when military pilots retire or finish their tours, they bring their Gen 3 experience to the private sector. Lately, petroleum companies, medical transports, pipeline patrol outfits, and even mosquito-spraying companies are clamoring to certify their aircraft and crews to fly with NVGs.
The FAA, not wanting to duplicate the entire history of NVGs in the military, 10 years ago began developing guidelines for civilian use. Unlike police units, civilian operators must get FAA approval for their goggles, interior lighting systems, and training programs. On tap for next year are minimum standards for goggle performance, in part to prevent pilots from using substandard night vision equipment now available from "Eastern bloc countries," says FAA rotorcraft specialist William H. Wallace. Bell uses NVGs made by Northrop Grumman; that company and ITT Industries are the principal U.S. manufacturers of the devices.
Until the civilian rules are in place, FAA approvals are granted on an individual basis and can be somewhat ad hoc. In 1999 Rocky Mountain Helicopters became the first air taxi company to earn FAA approval to use NVGs for its EMS helicopters. The company later was bought by Denver-based Air Methods, where Fridd is an NVG instructor.
Chuck Antonio, a former Navy fighter pilot and flight surgeon who later helped develop the NVG training programs for various aircraft in the Navy, Marines, and Air Force, leads a government and aviation industry committee that is advising the FAA on formulating the rules. Based on the military's experience then and now, Antonio believes most NVG accidents are caused by inadequate training, poor crew coordination, and flying too fast for the limited contrast and visual cues that NVGs provide. Antonio studied Air Force, Navy, and Marine accidents in fast-moving jets like the F/A-18, AV-8B, F-16, and A-10 and found that pilots would neglect their flight instruments in favor of the emerald world outside and become disoriented.
The military's safety record today is probably better than it was in the early days, but it's hard to tell. From 1980 to 1989, the Army alone had 79 accidents and 32 fatalities involving helicopter crews wearing NVGs, prompting an investigation by Congress, and the Marines had a similar rash of crashes. As a result the military delved into the human factors issues behind the incidents and created specialized night vision training programs starting in the early 1990s. As for the safety record, experts like Antonio say it's difficult to get a feel for trends since the military is conducting more and more complex night operations with goggles. "This undoubtedly leads to more risk and therefore a greater opportunity for mishaps," says Antonio.
A search of the National Transportation Safety Board's accident records for civilian or government-owned aircraft turned up only one accident where NVGs appeared to play a role. A crash of a Bell OH-58A on October 22, 2001, in Bartow, Florida, killed the police department pilot and observer when the helicopter hit the ground in a swampy area one mile from the departure airport. Though the NTSB found goggles in the wreckage and deputies who had flown with the pilot stated that he had "always used" NVGs for night flight, including landings, the board ruled that continued flight into instrument weather conditions and failure to maintain altitude were the probable causes, not the goggles. The sparse accident record may be a result of the newness of NVGs to the sector, or a byproduct of missions that are less sporty than the military's. "We're not flying nap of the earth, just using [the goggles] to avoid obstacles in getting from point A to point B," says Fridd of the EMS community. Baxter, a member of Antonio's advisory committee, says the industry wrongly believes that pilots with NVGs will fly into clouds and have no clue how to get back out. "It gets back to the training issues of how we identify poor weather," he says. "We teach techniques that help you avoid it." (Bell, which has been training police pilots how to use NVGs for years, got FAA approval to teach civilians in 2002.)
Those weather-avoiding techniques emerged in part from experience in combat operations in the Persian Gulf. In 1987, as a new Army pilot with 17 hours of NVG time, Baxter took part in a classified mission called Operation Prime Chance, designed to escort Kuwaiti oil tankers out of the Persian Gulf during the Iran-Iraq war. The mission called for crews to fly armed OH-58 helicopters at night, 20 feet above the water, to protect the ships from attacks by smaller boats and to deter the Iraqis from laying mines. "It wasn't doable without goggles," Baxter says. Some say Prime Chance, which ended after two years, was the first successful night combat operation performed entirely with NVGs.
The mission gave Baxter 1,100 hours of flying time, 500 with NVGs. That experience was of great comfort when, during my autorotation, I looked in vain for the 407's landing light to strike gold or hit rock.
No sooner had I called out "I have it" (the ground in plain sight) than Baxter, who with his NVGs knew where he was going all the time, yanked the rotor pitch control up just before we plunked down and skidded 100 feet down Bell's practice runway, a landing that looked easy because of the right training, the right equipment, and the NVG's magic emerald image.
Then Baxter, like every good pilot, issued the requisite self-critique. "I coulda used even less runway," he said.
Sidebar: The Physics of NVGs
NVGs amplify ambient light that is virtually undetectable to the naked eye and convert it to the visual spectrum on two-dimensional screens in front of each eye. In each tube of the goggles, photons reflected from an object enter through optics that focus the image of the object on the front side of a gallium arsenide photocathode. The photocathode ejects electrons from its back side in proportion to the amount of photons coming in from the front. The process is accelerated by an electrical field that is generated by two AA batteries mounted on the helmet.
The freed electrons ricochet through a micro-channel plate, a thin wafer the size of a quarter with 10 million tiny glass tubules offset eight degrees from the incoming stream and coated on the inside with a material that releases additional electrons with each ricochet, amplifying the input signal thousands of times. The cascading electrons light up a phosphor screen in the eyepiece, painting just an inch or so from the pilot's eyes a representation, in shades of green, of the scene outside.