Friday, August 17, 2018
Transport Canada - Aviation Safety Letter Night Vision Goggles Blind to LED Lights

Night Vision Goggles Blind to LED Lights

by Stéphane Demers, Civil Aviation Safety Inspector, Rotorcraft Standards, Standards, Civil Aviation, Transport Canada

Aviation eats up technology at an ever-increasing speed. Today, we see numerous technological advances being adapted from the military and from other areas into a broad spectrum of aviation-related applications.

Night vision goggle (NVG) technology is becoming mainstream, especially in the rotorcraft community. The ability to have a discernable horizon, see terrain details that were previously masked by darkness, and greatly increase night-operation safety makes the decision to use NVGs a wise choice. Pilots who use NVGs regularly now consider unaided night operations more of an emergency measure and would reluctantly fly without them.

Light emitting diode (LED) lights are another great tool, and their use is fast becoming the norm. In the past two to three years, these little lights have made their way into all forms of lighting fixtures, from tiny flashlights to automotive lights. In aviation, LED lights are now being used for obstruction and aircraft lighting. LED bulbs have a terrific appeal because they last much longer, and their size allows for more flexibility in designing navigation lights and beacons.

Ironically, we have inadvertently combined two technologies without fully calculating their impact on each other. In the past year, I have received numerous complaints from military, police, and emergency medical services (EMS) pilots indicating that their NVGs could not discern LED lights.

I first encountered this problem while working as a heliport inspector in Alberta, testing portable lighting systems for heliports. During testing, the pilots reported being unable to see green LED. We initially believed the colour was causing the problem: NVGs tend to make everything appear in greenish hues, and so we thought they must be drowning out the green LED.

Within weeks of our testing, we received other calls, but now about red and white LED lights. A military crew operating near a wind farm in Ontario reported that their NVGs could not see the red obstruction lights on the windmill towers. Some Royal Canadian Mounted Police (RCMP) pilots had reported being unable to see red LED lights on towers and on some automobiles; red LED Christmas lights were also invisible.

As the problem became more widespread, we contacted the National Research Council Canada (NRC) in Ottawa, Ont., to look into the matter. Dr. Gregory Craig confirmed that the NRC crews had made the same observation in their work. Dr. Craig provided the following numbers on NVG sensitivity and the LED spectrum (all measured in nanometres). The bottom line is this: The most commonly used LED lights peak at 623 nm; NVGs begin “seeing” at 645 nm and peak between 660-850 nm.


Photo: Jeff Calvert

Night vision goggles are becoming mainstream

Some LED lights peak at around 660 nm and would thus be visible to NVGs. However, it is unclear how prevalent their use is. The easy answer would be to simply use 660 nm LED lights. However, current regulations do not specify this nanometre reading as a requirement.

Furthermore, current obstruction lighting regulations do not require towers of lower than 300 ft to be lit unless they are an obvious hazard to aviation—such as very close to an airport or along an air route. This regulation has some flaws as it was conceived with fixed-wing operations in mind. However, the heaviest use of NVGs occurs away from those areas and often at or below 300 ft. As NVGs gain popularity, more fixed-wing aircraft will undoubtedly be using them. It may also be possible to see pipeline, wildlife, anti-poaching patrol, police, or even spray aircraft using them, all of which operate at or below 300 ft as required by their missions.

As Transport Canada Civil Aviation (TCCA) and the NRC continue to work together and with other interested agencies, it is important to get the word out to industry that obstructions may not be lit even when you think they should be. For those using NVG technology, be aware that you may not see LED lights on towers or even on another aircraft.

So, going night flying anytime soon? Check NOTAMs, plan your route carefully, do a dry run during daylight hours (if possible), and mark obstructions on your map or in your global positioning system (GPS). And remember that while your NVGs are a great tool, they do not exactly turn night into day. So keep vigilant, and take the odd peek outside under your nogs just to spot those elusive LED lights.

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