Dancing in the Dark
Night vision goggles can save a pilot's life or, if he hasn't had adequate training, take it.
- By John Croft
- Air & Space magazine, November 2004
USAF/Tech. SGT. Scott Reed
(Page 4 of 5)
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.