Nakagawara VB, Montgomery RW, Wood KJ. Laser illumination of flight crewmembers by altitude and chronology of occurrence. Aviat Space Environ Med 2011; 82:1055–60.Introduction: The illumination of flight crew personnel by lasers while they perform landing and departure maneuvers has concerned the aviation community for the past two decades. This study examines the frequency of illumination events in the United States by altitude and chronology of occurrence to determine where and when aviators and the flying public may be at greatest risk. Methods: Reports of aircraft illuminated by high-intensity light sources are maintained in a database at the Federal Aviation Administration's Civil Aerospace Medical Institute. Reports of flight crewmembers exposed to lasers from January 1, 2004, to December 31, 2008, were collected and analyzed. Results: Cockpit illuminations at or below 2000 ft (~610 m) increased from 12.5 to 26.7% over the 5-yr period, while the percentage of illuminations between 2000 and 10,000 ft (~610–3048 m) decreased from 87.5 to 58.4%. The months of November and December had the highest frequency of laser events (23%), while May and June had the least (12%). Sunday was the most likely day for an aircraft to be illuminated (18.3%), while Wednesday was the least likely day for such an incident (15.4%). More than 91% of all aircraft illumination events occurred between 1800 and midnight. Conclusion: The continuing increase in the number of laser illuminations reported at or below 2000 ft (~610 m) represents an escalating threat to aviation safety. Information provided in this study may allow law enforcement to deploy their resources more efficiently to apprehend those responsible for these crimes.