According to FAA documents, air traffic controllers across the country have violated new regulations intended to prevent sleeping on the job almost 4,000 times since they were instated.

Instances of sleeping on the job and other violations were reported from January through May at over 50 percent of airport control towers throughout the U.S., according to an internal FAA memo issued June 4.

The new rules were enacted after an air traffic controller was napping while working the midnight shift alone at the Reagan National Airport tower near Washington last year. Pilots of two separate flights were forced to land on their own when they received no reply from the napping controller supervisor.

The regulations disallow solo midnight shifts for controllers and require nine hours of rest between shifts. These and other rules were violated when instances of shift trading and scheduling snafus allowed several controllers to work 40 hours in just four days.