A study released today concludes an increase in sightseeing helicopter tour crashes in Hawaii due to poor visibility is possibly related to a 1994 regulation setting a high minimum altitude for flying.

But the Federal Aviation Administration disputes that, saying there is no link between the regulation and pilots flying into bad weather.

The study, conducted by the Center for Injury Research and Policy of the Johns Hopkins Bloomberg School of Public Health in Baltimore, noted that there was a decrease in the number of helicopter crashes in the 13 years after the regulation compared with the 13 before.

But the study, which will appear next month in a peer-reviewed monthly journal, “;Aviation, Space and Environmental Medicine,”; reported eight fatal crashes before the rule and eight after. “;The proportion of crashes that were fatal increased due to the increase in VFR-IMC (poor visibility) crashes, which have a high fatality rate.”;

The regulation, which became effective in October 1994, required air tour helicopter pilots to fly a minimum of 1,500 feet above the ground. According to the study, the rule was implemented to address the increasing number of air tour helicopter crashes. But some helicopter air tour pilots say the rule was adopted to address noise complaints.

Researchers who conducted the study found an increase in the crash rate attributed to poor visibility. The number rose from two crashes between 1981 and 1994, or 5 percent, to seven crashes between 1995 and 2008, or 32 percent.

Researchers concluded the regulation might influence helicopter pilots to fly at altitudes where clouds are prevalent. Researchers recommended the FAA return to allowing helicopters to fly 300 feet above urban areas.

FAA spokesman Ian Gregor said officials reviewed the 1,500-foot minimum altitude regulation for air tour operators in 2007. Their review involved examination of every Hawaii air tour accident that occurred 13 years before and after the regulation took effect.

Based on the review, officials found “;no causal link between the rule and pilots flying into bad weather,”; Gregor said in a written statement. “;The rule is not responsible for pilots flying into bad weather.”;

The National Transportation Safety Board also did not identify the 1,500-foot regulation as a contributing factor in weather-related crashes that occurred in Hawaii.

The Associated Press contributed to this report.