Introduction:Illumination of civilian and military aircraft by laser beams in the National Airspace System (NAS) has concerned the aviation community for nearly two decades. The principal concern is the affect laser exposure may have on flight crew personnel during landing and departure maneuvers when operational requirements are critical. This study examines the frequency of aviation-related laser event reports by month, day of the week, and time of day. Methods:Reports of aircraft illuminated by high-intensity light sources have been consolidated from multiple information sources into a database maintained by the Civil Aerospace Medical Institute's Vision Research Team. Laser illumination event data involving civilian aircraft in the United States for a 5-year period (January 1, 2004 to December 31, 2008) were examined for this study. Results:There were a total of 2,492 laser events in the U.S. during the study period. In 1,676 (67.3%) of these, the cockpit environment was illuminated by a laser light. August through December were the most active months with 51% of all reports, while May through July were the least active with only 19% of all reported incidents. Sunday was the most likely day of the week for an aircraft to be illuminated by a laser (15.4%), with a relatively high number of aircraft illuminations occurring on Friday and Saturday. Weekdays exhibited the fewest laser illumination events. Time of day was provided in 2,429 (97.5%) aircraft laser illumination reports. Approximately 69.8% (1,696) of the aircraft illuminations occurred between 7 p.m. (1900 hours) and 11 p.m. (2300 hours) during the study period. Conclusions:Laser illumination events are most likely to occur from late summer to early winter months and on weekends between 7:00 p.m. and 11:00 p.m. Both weather conditions and daylight savings time may play important roles in determining an opportune time frame for laser activity in a particular locale. Knowledge of these findings may assist the aviation community and law enforcement officials in allocating their limited resources to increase the likelihood of apprehending those responsible for these criminal acts.