An investigation into two near-misses at O’Hare Airport points to a perennial safety problem. The Federal Aviation Administration is now evaluating whether air traffic controllers face a recurring pattern of fatigue.

Air traffic controllers’ work schedules aren’t just long, they’re irregular. Sometimes, a controller can finish one shift and then have to show up again just eight hours later. Two close calls at O’Hare have the FAA reviewing whether that provides enough time for a good sleep.

But O’Hare air controllers’ union rep, Jay Moffat, says there’s little that can be done. Controllers must know how to work any shift, be it day or night.

“Across 25 years, all the variations we’ve tried, we’ve never come up with anything that is better than what we’re currently doing,” Moffat says.

The air controller’s union says it’s not clear whether fatigue caused the mishaps in the first place.

The National Transportation Safety Board listed several other reasons as well, though it did ask the FAA for the sleep deprivation review.