DALLAS (CBSDFW.COM) – The FAA is investigating a window that cracked on a Southwest Airlines jet during flight.

The airline said the pilots did not declare an in-flight emergency on Flight 957 from Chicago to Newark, but did divert the Boeing 737 to Cleveland.

Kara O’Grady sat in the same row as the window that cracked. “It just sounded like a really loud pop, like someone throwing a rock at you.”

(photo credit: @ChaikelK/Twitter)

Photos of the window quickly appeared on Twitter.

They show the outer pane of the emergency exit window cracked.

Each exit row has three panes of glass.

O’Grady said, “It was a little frightening. I fly all the time for work and this is the most disturbing flight I’ve ever had. But the Southwest flight crew was very professional, they were very calm.”

She said the flight attendants moved them to other seats, and that the cabin remained pressurized at all times.

Passenger Rachel Colby said it was still a little unnerving. “I just said to my friend that was sitting next to me that that’s not normal, I’m not sure what that was. We kinda looked back behind us and there was some scurrying of some people that were kind of a little frantic.”

Like O’Grady, she praised the flight crew. “Everything was handled so well by Southwest honestly. It was smooth, we all felt comfortable, we all felt safe.”

The incident comes two weeks after another Southwest jet experienced an engine failure that sent shrapnel flying, and breaking a window.

A passenger, 43 year old Jennifer Riordan of New Mexico was killed.

The NTSB is investigating that case.

As for the cracked window on the jet Wednesday, they are rare.

Experts say there have been 26 failures of the outer window pane in the entire worldwide service history of the Boeing 737.

Retired airline captain Denny Kelly praised the Southwest pilots. “They did exactly as they should do. They landed the airplane.”

Kelly said there’s no telling what will happen to a cracked window. “They could have flown for another hour and it could have blown out. You just don’t know.”

Kara O’Grady said, “It was a freak thing. The Captain was great, the crew was great. But it’s something, I fly all the time and never had something that weird, freaky happen to me before.”

Southwest passengers in Dallas CBS11 spoke with are taking the news in stride.

John Dowdy who was headed home to St. Louis after a business trip to Dallas said, “I have no worries. Southwest has a good track record, so I’m sure they’re going to take care of it.”

The airline said it removed the jet from service, and that safety remains its top priority.