Nov 13 2014

Enhanced Vision Options for Helicopters Posted 10 years 46 days ago ago by Admin

 

In a perfect world, helicopters would always fly in bright, clear skies, all obstacles would be consistently visible, and dust would never obscure a landing zone. In the real world, visibility is an ongoing issue for helicopter pilots. Seeing through fog and dust is a challenge at best, and impossible at worst. Meanwhile nighttime flying, with its lack of contrast and hidden obstacles, can be a deathtrap for the unwary.

Fortunately, there are a number of enhanced vision systems available for today’s helicopter pilots. All provide better visibility in one way or another – and all have their limitations as well. This is why savvy helicopter pilots use them as tools to make flying safer, but remain mindful that no perfect enhanced vision solution exists.

Night Vision Goggles

When most people think of enhanced vision solutions, they think of night vision goggles (NVGs). In use in one form or another since World War II, NVGs operate by capturing ambient nighttime photons through a front lens and converting those photons into electrons using an image intensifier tube. These electrons are then sent through a micro-channel plate to increase their number, and then projected onto a phosphorus screen to convert the amplified electrons back into visible light that a viewer can see through the eyepiece. Because the color of the phosphor used is green, the image portrayed on the eyepiece lens is monochromatic green.

NVGs have evolved through a number of generations since they were first developed. Over time they have improved their ability to work in extremely low-light conditions, to provide sharper images, and to deal with sudden inputs of bright light that can overload the system and temporarily blind the viewer.

Extremely effective for most nighttime VFR helicopter operations, NVGs have become the standard for most EMS and law enforcement operations. This movement to NVGs in the civil helicopter markets over the last decade has had one of the greatest impacts on improving safety in nighttime helicopter operations.

That said, some NVG limitations still exist. They include a narrow field of view (typically 40 degrees), an inability to provide accurate depth perception to the wearer, and susceptibility to blooming when hit by a strong external light source or cockpit lighting that’s too bright. This is why many helicopter operators who rely on NVGs have their cockpits retrofitted with NVG-compatible lighting systems.
    
NVG systems are not designed to be used out of the box. To fly with them safely, helicopter pilots must be trained first. It’s not just a matter of learning to interpret the NVG images accurately. Even when wearing them, pilots need to retain situational awareness around the aircraft, which includes paying attention to light cues outside the NVGs’ field of view.

A case in point: In June 2013, two Royal Navy Lynx helicopters came within 50 feet of each other before anyone noticed. Both aircrews were wearing older NVGs and failed to notice the other aircraft outside their NVGs’ limited fields of view. According to the U.K. Airprox Board, which investigates near misses in British airspace, “The safety margins were reduced so far below normal that the situation had only just stopped short of actual collision.”

Onboard Camera Systems

Helicopter-mounted video camera systems are another option for enhancing visibility for rotorcraft pilots. Thanks to advances in technology, these camera systems feature high-resolution video not just in visible light, but also in the near infrared (NIR) and short-wave infrared (SWIR) bands.

Highly useful NIR and SWIR sensors can provide usable imagery in moonlight, starlight, and ‘nightglow,’ the faint light generated by the Earth’s atmosphere. NIR/SWIR sensors can also capture enhanced images by using short-range lighting (arrays of LEDs) or long-range illumination (aircraft-mounted laser beams and/or specialized spotlights).

One major benefit of SWIR camera systems is their ability to see through fog and dust. The latter quality is a major benefit when landing in desert conditions where prop wash can reduce visibility to zero.

Modern onboard camera systems, such as FLIR’s Star SAFIRE 260-HLD (HD laser designation), come with a range of sensors built into their camera enclosures. These include an IR sensor (640 x 480 lines of resolution), color HD CCD sensor (1080p HD), EMCCD (electron multiplying CCD for enhancing low-light images) and a laser designator, range finder, and illuminator/pointer.

The downside of using camera systems for enhanced vision include the need to keep checking the display to review imagery while flying; the requirement to track the camera manually for ongoing situational awareness, and the lack of depth-of-field due to the camera showing a monocular 2D image.

Max-Viz Enhanced Vision System

The Max-Viz Enhanced Vision System (EVS) is an interesting take on seeing in poor visibility conditions. Using an externally mounted camera connected to a cockpit display, the infrared-detecting EVS displays differences in heat, rather than differences in light.

The immediate benefit of EVS is that it can provide clearly defined imagery in extremely uniform, low-light conditions, such as haze, smoke, dust, or fog. It is also useful in areas that lack ambient light sources, such as overcast nights in remote areas where power lines and tall trees may be present, but human lighting, moonlight, and nightglow are not.

“The idea of Max-Viz EVS is not to replace a NVG solution, but to supplement it,” said Bob Yerex, Max-Viz’s director of rotorcraft sales and business development. By using thermal imaging, Max-Viz captures images that NVG can miss – and vice versa. Meanwhile, by offering a wider field of view than NVGs, Max-Viz EVS can help pilots avoid threats that lie directly in front of the aircraft.

“Weather-related accidents in rotorcraft occur – or are initiated – most often from cruise flight,” Yerex added. “Because EVS is generally much more effective in detecting the differences between a marginal VFR environment and one that is IMC, the fixed-mount design allows for much earlier and more effective avoid/abort decisions rather than penetrating the conditions in an unintentional manner.”
        
Marenco’s High-Visibility Cockpit

Sometimes enhanced vision doesn’t require advanced electronics. Sometimes it is simply providing the pilot with as much visibility in all directions – including up and down – by just maximizing the aircraft’s glass.

This is the concept behind the Marenco Swisshelicopter high-visibility cockpit, which has been built into the company’s SKYe SH09. Wherever possible, the pilot and copilot have nothing in front of them but glass, supported by the thinnest and most unobtrusive of support frames. Looking out front from the cockpit, all one really sees is the outside world, including when looking down or up.

“Our enhanced vision concept is, before everything else, neither an electronic device nor a mechanical part but simply our wide opening to the outside,” said Mathias Sénès, Marenco’s chief commercial officer. “The wide Plexiglas windows to the front, to the side, and a glass floor will bring added safety to outside landings in unprepared terrains, giving a view to the cargo when working with external loads, and also enhance surveillance missions.”

The only bad news is that the SKYe SH09, designed as an eight-person utility helicopter, is still under development. The prototype was unveiled in December 2013, and Marenco is aiming at producing the first units this year, with delivery starting in 2015. For the record, the SKYe SH09 will be built with composite materials, have a bearing-free five-blade system, a shrouded tail rotor for safety and reduced noise, and a single Honeywell HTS900-2 turbine engine with full authority digital engine control (FADEC).
    
Conclusion: No One Size Fits All

It is a good thing that a range of enhanced vision technologies exists, as no single system covers everything. In fact, there are poor visibility situations that even a combination of every available technology might not cover. That said, using NVGs, camera systems, EVS, and maximum glass will help improve the odds.

Moreover, no system can replace the pilot and their conscious duty to maintain situational awareness at all times. Sometimes the best system is simply to accept when it is not safe to fly, and to stay on the ground until conditions improve.