In the rush to save energy by replacing incandescent light bulbs with LED (light-emitting diode-based) lights, airports and the FAA are trying to deal with visibility issues caused by LEDs installed in the runway environment.
On Dec. 19, 2007, President George W. Bush signed into law the Energy Independence and Security Act. One of the stipulations in the law mandated improved light bulb efficiency and not, as many believe, an outright ban on incandescent bulbs. Nevertheless, as a result of this law some airports have switched to LED lights for runways and taxiways and obstruction lighting, apparently without considering how LED lights can affect visibility for pilots. This is of particular concern during night approaches because airports have had a problem matching the intensity of LEDs to that of approach light systems. In a situation where incandescent approach lights are comfortably viewable by pilots, LED runway and taxiway lights can emit much brighter light, according to NBAA, “causing pilots to be blinded by the brighter LEDs.”
Pilots’ reports about relative brightness in the NASA Aviation Safety Reporting System database, though few in number, confirm that there is a problem. AIN was able to find three such reports, one of which was filed before the new law was enacted. In this 2006 report, the pilot wrote, “I feel there are [problems] with the new LED [taxiway] lights. In ATL, they are replacing the old incandescent lights with new LED lights. They are very bright, making it difficult to taxi. Please look into this as it is a big human-factors event waiting to happen.”
A 2011 report by an airline pilot using Albuquerque (N.M.) International Sunport complained about LED runway, taxiway and airfield marking lights. “When I landed, the lights throughout the airfield were on low, and they were exceptionally bright. The excessive brightness, particularly in the approach and flare, can lead to a lack of depth perception and could lead to very poor landings and touchdowns. The lights are so bright it leads to a loss of night vision not unlike a light being flashed directly in your eyes. The turn-off taxi lights are also disorienting as they reduce depth perception due to ‘flash’ blindness.” This pilot recommended “a thorough test of the effects of LED lights on pilots’ vision needs to be accomplished. The LEDs are not good…[and] could lead to a disorienting situation.”
Two years ago, the captain of an Embraer EMB-135 wrote a report about taxi lights at Richmond International Airport in Virginia. “The problem is these lights aren’t able to dim. When it is pitch black outside, it is very annoying and difficult to taxi with extremely bright taxi lights. The green taxi centerline lights are the worst. I have asked controllers numerous times if they could dim them and have always been told that they are either not able to dim or they are already on the dimmest setting. The bright taxi lights are an unnecessary hazard. While they might not directly cause an accident they are more than capable of being another link in the accident chain. Is there any way that these lights can be dimmed?”
The FAA asserts that its William J. Hughes Technical Center in Atlantic City, N.J., and Airport Engineering Division (AAS-100) have addressed pilots’ issues with runway lighting. The solution involves replacing three-step regulators with a five-step version, as specified in Advisory Circular 150/5340-30H. “This upgrade allows better control of the step (brightness) level,” according to the FAA. The agency also issued Engineering Brief 67D, which redefined “the dimming curves for white and color (red, yellow, blue and green) LED light fixtures based on pilot inputs, which has the effect of lowering the light intensity of LED runway lighting.” After making these changes, the FAA said, “We have not received any further brightness complaints from pilots on runway or taxiway lighting.”
Approach lighting systems haven’t yet been switched to LEDs. It turns out, according to NBAA, that two different FAA departments control airport lighting. Runway, taxiway and surface lighting falls under the jurisdiction of FAA airport personnel, NBAA explained, while FAA technical operations personnel control approach lighting systems and visual approach path indicators. So far, LED approach lights have been installed at only one U.S. airport, the FAA’s Hughes Technical Center in Atlantic City, where testing continues. Green LED threshold lights have been tested at two public airports–Phoenix Sky Harbor and Grand Forks International in North Dakota–with encouraging preliminary results, according to the FAA.
Last October, the FAA invited industry representatives to a symposium on LED lighting. “The agency said it intends to sponsor the development of an LED flight-test plan, which will include all the appropriate FAA services and offices, as well as input from those in the aviation industry who wish to participate,” NBAA explained after the meeting. NBAA also reached out to pilots, asking for feedback about LED lighting problems at airports. Airports are supposed to report installation of LED lights to the FAA to provide information for an FAA LED database.
LED and Enhanced and Night Vision Systems
While LED lights last longer, are more reliable and use less electricity, they are not visible by infrared enhanced vision systems (EVS) or night-vision imaging systems (NVIS).
According to a 2009 FAA Safety Alert for Operators, “Aviation Red light ranges from about 610 to 700 nanometers (nm), and NVGs approved for civil aviation (having a Class B Minus Blue Filter) are sensitive only to energy ranging from 665 to about 930 nm. Because LEDs have a relatively narrow emission band and, unlike incandescent lights, do not emit infrared energy it is possible for them to meet FAA requirements for Aviation Red but be below the range in which NVGs are sensitive.” LED lights used to illuminate obstacles may be below the range detectable by NVGs. “Crews that fly using NVGs are warned to use extra caution when flying near obstacle areas and to report any hazardous sites to the nearest Flight Standards District Office (FSDO) or the appropriate military Safety Officer.”
The issue of how LEDs in approach lighting systems could affect pilots was brought up in a 2009 letter to the FAA from avionics manufacturers Elbit (Kollsman) and CMC Electronics, airline Federal Express and aircraft manufacturers Gulfstream and Bombardier. They noted that to be effective for EVS users, LEDs “must maintain a minimum requirement of 48 Watts of irradiance per emitter in the [1,300 to 2,400 nanometer] spectrum.”
With regard to EVS, the SAE G-20 committee was formed in 2010 to study interoperability issues with LEDs. The committee is involved in the testing at the Hughes Center. The NVIS efforts have been combined with the work being done by the Operational Flight Test Group formed at the October symposium. “We expect to see recommendations and results from this group this calendar year,” the FAA noted.
One solution to the incompatibility with EVS is to embed an infrared emitter in the LED bulb that makes the bulb visible to pilots using EVS or night-vision goggles (NVG).
Rockwell Collins has taken a different approach and developed the multi-spectral EVS-3000, which has two sensors, one for heat-emitting infrared sources and one for LED lights, ensuring that pilots can see LED runway lighting in EVS displays.
Meanwhile, NBAA is working with the FAA and other industry stakeholders to resolve issues related to LED airport lighting, both on runways and taxiways and for the approach. John Kernaghan, member of the NBAA Access Committee’s airspace, air traffic and flight technologies subcommittee, explained that the next step is flight-testing at the Atlantic City installation. This will involve all types of operators, from airlines to charter and Part 91 corporate and light aircraft, including some equipped with enhanced flight vision systems. The testing will include seemingly arcane issues such as aircraft with and without windshield wipers. “There are lots of variables going into this,” he said. “Right now we’re coming up with the flight-test protocols.”
“Everything and anything is on the table,” he said. Solutions could involve separate LED and incandescent lighting that could be switched when necessary, or adding infrared emitters to LED bulbs. It all comes down, he said, “to what is the most effective equivalent.”
NBAA will place a link to an online survey on its website to seek more input from pilots on LED lighting issues. “If somebody experiences an issue with LEDs, whether positive or negative, we want feedback,” Kernaghan said. “It’s truly a team effort between the FAA and industry stakeholders to come up with a viable system that offers one level of safety.”