Federal Aviation Regulations part 91 cover such issues as the age of pilots, how much flight experience a pilot has, and the risk for every pilot of being in a crash based on age and experience. Basically, the FAA does not allow any pilot to fly past the age of 60 years. This age limit has been set based on few studies but more research is currently being done investigating age, experience, and crash risk. One recent study found that pilots with over 5,000 hours of flight time had an almost 60 percent lower risk of crashing. It follows that these pilots, with high flight times, would be older pilots. Federal Aviation Regulations Part 91 also covers other pilot issues that can affect commercial flights. One concern is the prevalence of alcohol in the flight industry. Pilots and air crew fly long hours and have extended layovers, both of which sometimes lead to substance abuse in some people. To combat this problem the FAA has instituted a strict drug testing program for all employees.