Terry McVenes, a safety advocate at the Air Line Pilots Association, said Monday that FAA regulations should be modified.
"They were written 50 years ago when airlines flew piston planes and the types of schedules we see now weren't even contemplated," he said.
Pilots at some airlines had negotiated more restrictive rules for crew rest, but those have been relaxed in recent years as airlines have lost money and struggled to increase pilot productivity.
"The competitive economic environment in the airlines has brought all kinds of labor concessions," McVenes said. "Pilots are flying right up to the legal limits, and we really need to look at this back-side-of-the-clock flying and understand effects on safety and pilots' long-term health."
There was only one air traffic controller in the tower at the time of the accident, and that person had to coordinate several departures, ground movements and make weather reports.
Air traffic controllers are responsible for ensuring pilots are given the correct clearances and read them back properly, but they don't watch each airplane to make sure the crews follow instructions. Each airline captain is ultimately responsible for that.
The NTSB's Hersman said the lights on Runway 26, the short runway, were inoperative, and it would have been impossible for the air traffic controller to turn them on from the tower.
Air operations were nearly normal Monday, with another Comair jet filling in for the plane that was lost.
Sherri Miller of Richmond, Ky., stopped briefly at the airport's chain link fence to attach a bouquet of yellow flowers in remembrance of the people who perished.
"I knew Judy Rains," she said of a Lexington dog groomer who died on the way to St. Louis where she was to be married. "She groomed my dogs and she was a friend. But these flowers aren't just for her. They're for everyone who left us."
Experts say FAA should act on NTSB recommendations after Lexington
It was unclear Monday just when the pilots might have realized they were on a runway too short for their plane.
The FAA acknowledged violating its own policies when it assigned only one controller to the Lexington tower.