As it is a safety concern, the NTSB did release a safety recommendation to both the FAA and the NATCA. The issued recommendation analyzed four controller faulted runway "incursions" where, after investigation, the respective air traffic controller showed signs of fatigue. The report said, "Fatigue is known to degrade performance on cognitive tasks involving working memory and vigilance", and that the mistakes made by the controllers in the investigated instances were consistent with signs of fatigue. The board attributed this fact to both the shift-work used at most facilities which often does not allow sufficient rest time between shifts, and to the increase amount of overtime worked due to the decrease in controllers.