The delayed delivery of a laser has held up evaluations of the US Federal Aviation Administration's guidelines for laser exposure within 10 nautical miles of an airport. The tests, which were scheduled to begin earlier this year at the agency's Mike Monroney Aeronautical Center, were put off until a laser is received and set up. Many scientific experiments that use outdoor lasers also have airplane tracking systems to prevent the beam from interfering with a pilot.Van Nakagawara, vision research team coordinator, said researchers hope to begin testing in a few months. Using a flight simulator, they plan to test about 30 pilots, in two situations -- a standard instrument landing and a departure with a steady-state turn. During the simulation, the pilots will be illuminated with a 5-µW/cm2 burst of 532-nm light from a frequency-doubled Nd:YAG. This level can create a veiling glare that is about as bright as the high beams on an automobile, said Greg Makhov, president of Lighting Systems Design Inc. in Orlando, Fla., and a member of the research group. The burst of light is the maximum amount of uncontrolled laser light permitted within the aviation administration's 10-mile "critical flight zone" around an airport. The group had planned to use an argon-ion laser but chose an Nd:YAG instead because it needs less maintenance. "The ideal laser," Makhov said, "would be a 1-W, continuous-wave, diode-pumped, frequency-doubled Nd:YAG. The stumbling block is that nobody wants to give up their laser." The group plans to fiber-couple the laser into the flight simulator cockpit and to bracket the exposures to include 1-s bursts at 0.5 and 50 µW/cm2, which are still below the maximum permissible exposure level set by the American National Stan- dards Institute. The project is a collaboration among researchers at the Federal Aviation Administration, Brooks Air Force Base in Texas and the International Laser Display Association, a group of laser light show firms that will help set up the experiments. These companies hope a review of the federal guidelines will lend them scientific credence. This, said Makhov, should ease pilots' fears that the current guidelines were not established with the cockpit work environment in mind. British guidelinesAcross the water, officials at the Civil Aviation Authority in London recently revised the guidelines for outdoor lasers used within 10 miles of an airport. The new guidelines ask that laser operators notify aviation officials at least four weeks before use. They request a 20-W peak power cap on the lasers and ask that the beams be terminated by buildings or land features. If the beam termination is impractical, laser operators should arrange direct contact with airports so that the laser could be shut off immediately.John O'Hagan, principal scientific officer at the National Radiological Protection Board in Oxford, UK, which helped to establish the guidelines, said that pilots in the UK are more concerned with the dangers posed by high-power scientific lasers than with laser light shows.