Pilot Climbs in Through Window to Unlock Cockpit After Being Locked Out

A Southwest Airlines pilot was locked out of the cockpit before takeoff and had to climb in through the window to unlock the door.
The incident was witnessed by passengers, one of whom posted a photo on Twitter.
Southwest Airlines said this was an unusual occurrence.
The pilot unlocked the cockpit door from the outside and the flight departed shortly after.
Previous incidents of pilots being locked out of cockpits have occurred on other airlines.