KNOXVILLE, Tenn. (WVLT) -- Your pilot's shift starts well before your flight takes off. By the time they've made the takeoff announcement, some pilots have been in the air all day.

Commercial pilot and flight instructor Joseph Chance told us, "That's where most of the issue with airline flying and stress level for pilots is coming from is lack of sleep."

According to The National Sleep Foundation pilots don't sleep enough. They average 10 hour shifts. They also tend to commute more than 45 minutes to their base, or crash at hotels and even airport lounges.

Another flight instructor, Daniel Walters said, "You got to get your bags, you got to get on the bus, get to the hotel. Take a shower, decompress...Then by that time you only get 4-5 hours sleep because you've got to get up get packed, get on the bus, get to dispatch, figure out your legs for the day. It's just stressful."

Most airlines require eight flight hours a day, plus time just spent waiting.

"You've got to think about sitting on the tarmac where they're sitting with the engine running and getting just a little bit amount of air in the cabin," Walters added.

The physical demand is part of the reason commercial pilots have to meet rigorous physical and mental health requirements. The FAA won't give you a commercial pilot's license if you have a history of mental illness, but it doesn't always check pilot's mental status after they pass the initial test.

That's why Chance said, "You have to be kind of personally responsible for whether you're stressed out or not."