Investigators probing a commuter plane crash near Buffalo criticized federal regulators Thursday for failing to impose safety improvements that might have prevented the…accident…which killed 50 people…The National Transportation Safety Board (NTSB) investigation found that Colgan Air [part of Pinnacle Airlines]…did not act on the [Federal Aviation Administration’s] alerts. The alerts were not mandatory…safety alerts urged airlines to better train pilots in how to recognize and prevent fatigue…[;and] to identify pilots who had "persistent performance deficiencies" and to give them remedial training.