The parents of an 18-month-old who fell to her death from an open window on a Royal Caribbean cruise ship in July announced Wednesday that they are suing the cruise line, contending that the accident was the company’s fault.

Alan Wiegand and Kimberly Schultz Wiegand, of South Bend, Indiana, were on a Royal Caribbean cruise ship in Puerto Rico when their daughter, Chloe, fell out of an open window from the ship's 11th story while she was in the care of her grandfather, Salvatore Anello.

Salvatore Anello with his granddaughter Chloe Wiegand. Courtesy Wiegand Family

Anello, who had placed Chloe near a window prior to her fall, has been charged with negligent homicide in her death. The grandfather told CBS News in November that he “thought there was glass” in the window pane, adding that “if there was some kind of warning sign there, we wouldn't have ever been near it.”

The lawsuit says Chloe was with her mother in a children's water park area on the pool's 11th deck, and that when the mother had to go attend to another matter, Anello came to supervise the child.

"Mr. Anello was closely supervising Chloe as she played," the suit says. When at one point "Chloe walked over to a nearby wall of glass on the same deck," her grandfather followed her.

The wall of glass featured three rows of glass, floor to ceiling, with a wooden rail between the middle and bottom rows. Lipcon, Margulies, Alsina and Winkleman, P.A.

"Unknown to Mr. Anello at that time, this was not, in fact, a wall of fixed glass," the suit says. Instead, some of the glass panes in the middle row could be opened by anyone, including other passengers.

In addition, a wooden rail that was about 18 inches from the wall of windows kept Anello far enough away that he could not tell a window in front of him had been slid all the way open, the suit says.

The distance between the window and the railing. Lipcon, Margulies, Alsina and Winkleman, P.A.

Upon reaching the windows, Chloe asked to be lifted up so that she could bang on the glass as she frequently did at her brother’s hockey games, the suit says. Anello lifted her up onto the railing and held her as she leaned forward to bang on the glass that they thought to be in front of them.

But with no glass in the opening, "she slipped from Mr. Anello’s arms, falling through the open pane and down approximately 150 feet below" onto the pier in San Juan, killing her, the suit says.

“This is not some freak accident,” the Wiegands' lawyer, Michael Winkleman, told NBC News. “This is something that was a preventable accident.”

“These windows are entirely not compliant with the standard for windows on cruise ships,” he said.

“Carnival and [Norwegian Cruise Line] and even newer Royal Caribbean cruise ships have windows that are wholly compliant with these window fall prevention codes,” Winkleman said. The ship from which Chloe fell to her death did not though, he claimed.

Royal Caribbean told NBC News early Wednesday, “We have not been served with a lawsuit related to this matter and have no further comment.”

Chloe Wiegand Courtesy Wiegand Family

The Wiegands are seeking an unspecified amount of damages for their daughter’s death. In the suit filed in federal court in Miami, they say the cruise line failed to “provide reasonably safe children entertainment areas,” failed to “adequately mark the open windows,” and failed to “install safety prevention devices on windows,” among other grievances.