A United Airlines flight attendant mysteriously broke a huge rule and cost the airline a ton of money (UAL)

A United Airlines flight attendant on Monday intentionally deployed the emergency slide on a Boeing 737 in Houston, Texas.

The incident occurred about noon as United Flight 1246 pulled into the gate after arriving from Sacramento, California.

According to the airline, a female member of the cabin crew deliberately opened the right front door of the jet, deployed the emergency-evacuation chute, and jumped out of the aircraft.

The airline has removed the flight attendant from flight duties and reviewed footage of the incident with the employee. But United has not revealed what caused the flight attendant to engage in the mysterious act.

Although there was a medical situation reported on board, it was unrelated to the incident, United told Business Insider.

Flight operations at Houston's George Bush Intercontinental Airport were not delayed. The Boeing 737-900 was taken out of service, and the slide was refitted on the aircraft.

But the incident could cost the airline between $6,000 and $12,000 just to repack the undamaged slide into its container. Repairing and repacking a damaged slide could run as high as $30,000.

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