A Southwest Airlines plane flying from Chicago to New Jersey was forced to make an unscheduled stop after the outer pane of a window cracked.
Some on board immediately thought back to just two weeks ago when a jet engine blew apart and broke a window during another Southwest flight, killing one passenger who was partially sucked out of the window.
"It made you nervous because something like this just happened," said passenger Paul Upshaw of Chicago, who was about two seats from the window.
There were no reports of injuries after Flight 957 heading from Chicago to New Jersey landed safely after making an abrupt turn toward Cleveland, according to tracking data from FlightAware.com.
Photos taken by passengers and posted on social media showed one window with a large, jagged crack.
Some of the plane's 76 passengers said the crew quickly checked the window near an emergency exit and handled the situation smoothly.
"People just started scattering," said Mr Upshaw, who added there was no yelling or screaming.
"We didn't panic."
Dallas-based Southwest said that the plane was diverted to examine damage to one of the three layers in the window, but did not immediately release details on how it was broken.
Southwest Airlines spokeswoman Brandy King said there were no other mechanical problems with the Boeing 737.
Robert Mann, an airline consultant and former American Airlines executive, said windows are periodically polished to remove crazing, the formation of tiny cracks from exposure to chemicals and the sun's rays.
He said he couldn't recall a similar incident caused by crazing and that the pilots were right to make a quick landing.
The timing of the incident could hardly be worse for Dallas-based Southwest, the fourth-biggest airline in the United States.
Airline executives said last week they have seen ticket sales slow since the 17 April engine failure than sent debris flying into a plane, breaking a window and killing a passenger, 43-year-old Jennifer Riordan of Albuquerque, New Mexico.
Southwest estimates the drop in sales will cost it between $50 million and $100 million.
The window on the flight that landed in Philadelphia blew out after being hit by a loose engine part.
Ms Riordan died of injuries suffered after she was partially sucked out.