Friday, September 5, 2014
Lasers: The Continuing Threat to Aircraft
We have all seen the statistics concerning laser strikes versus aircraft over the last few years. Reported laser strikes on aircraft in the U.S. have increased from 300 in 2005 to 3,900 in 2013. These strikes can range in severity from a significant distraction, to a safety hazard which could cause an accident or temporary to permanent damage to the flight crews’ eyes.
I recently attended ALEA’s annual meeting in Phoenix, Ariz. where I went to a private briefing given by a gentleman who is developing an eye protection system to combat this threat. For now, my interest was engaged by the safety hazard these strikes present. I don’t believe all of the risks involved are well understood by the pilot community or their management.
Some homework to start with: Nanometers, abbreviated as nm, is the measurement of the wavelength of light. In lasers, blue light is 445-450 nm and green is 532 nm. Visible light is in the range of 400-700 nm. Infrared, abbreviated as IR, is light that measures above 700 nm and is invisible to the human eye. Milliwatts, abbreviated as mW, is a measurement of power output. There are one thousand milliwatts in a watt of power.
The FAA defines the risk of lasers by altitude and speed, and the lower and slower the aircraft is operating, the greater the risk. The U.S. Food and Drug Administration (USFDA) restricts laser pointers available to the general public to five mW, and in England that value is one mW. In a test conducted by the U.S. National Institute of Standards and Technology, lasers acquired on the general market exceeded 65 mW, 11 times the legal limit. In independent tests, lasers available for sale online have measured 2,000 mW, or 400 times the limit. Fact: The legal restriction on the power of lasers available to the public is ineffective. This fact is important because these elevated power levels raise the distance at which a crew could sustain eye injury by exposure to the light, or disorientation leading to an accident.
Green laser beams are generated by utilizing an IR diode source of 808 nm, then the frequency is increased, which changes the wave length to a value of 1,064 nm. That is then halved, resulting in a 535 nm green laser. So all laser pointers are required to have an effective IR filter, but that is obviously not the case. In tests, many of the higher powered lasers emitted as much as 77 percent of their total energy in the IR range. This is significant because the human eye reacts differently to green light and IR. Your eyes will blink and afford you some protection when exposed to green light, but not so to IR.
In reaction to this acknowledged threat, some operators have acquired “laser eye protection” for their staff. And regardless of their questionable effectiveness in the green spectrum of laser light, this still leaves blue, red and IR to contend with. In reality, what is more likely is that the bad optics, called low visual light transmission (VLT), of these cheap glasses may cause the crew to not wear them because of the detrimental effect on their night vision. If worn, and if they protect the user from the green band accompanying the IR light energy, they may do more damage to the users eyes because he does not perceive the IR threat that is present.
The way forward on this issue is multi-focused and includes a willingness by management to accept that this is a risk that they need to understand. For now, the only standard that really addresses this problem appears to be the European Union’s standard of En 207-208. The American standard at this time, ANSI Z136, is lacking in terms of visual acuity needed for flight operations, particularly at night. The FAA needs to come forward with an A.C. discussing this problem in real-world speak that doesn’t start by putting the onus on the crew to fly higher - blah, blah, blah. An aviation-derived standard needs to be established in the U.S. or, if appropriate, the FAA should adopt En 207-208. Finally, crews need to relinquish their prejudices about “it can’t happen to me,” and “the eye wear is too heavy, ugly,” etc., and realize that they only have one set of eyes, and a bad strike could cost them their career.