Which commercial aircraft can stay in the air the longest?
A commercial airship, like the 'Zeppelin NT' can stay airborne for 24 hours.

The record (for a military US-Navy blimp in the 1950s) is 264 hours, 12 min. It covered more than 13,000 km.


  Record flight of 8,216 miles in 264 hours. Lakehurst NJ to west Africa to Key West FL non-stop. (Source)