BILLINGS, Mont. (AP) — A United Airlines flight likely encountered severe "clear-air turbulence" over Wyoming when it began to lurch violently en route from Denver to Billings, causing injuries to 11 of the 114 people on board, federal safety investigators said.
A report from the National Transportation Safety Board said the Boeing 737-700 sustained minor damage in the Feb. 17 incident but continued on its way for an uneventful landing.
Two people were seriously injured, and nine people reported minor injuries.
Among those with minor injuries was a lap-held infant. Passengers had said a baby was wrenched from a parent's hold as the plane was shaken by the turbulence while travelling at an altitude of 34,000 feet.
The NTSB said clear weather was reported at the time of the event.
United has since returned the plane to service, The Billings Gazette reported Wednesday (http://bit.ly/1g8WAzh ).
According to the National Oceanic and Atmospheric Administration, clear-air turbulence "is the bumpiness experienced by aircraft at high altitudes (above 18,000 feet) in either cloud-free conditions or in stratiform clouds."
It occurs when undulations known as gravity waves in the upper atmosphere "become steep and unstable, then break down into chaotic motion," the NOAA said.
All but one of the injured, a female flight attendant, were released within a day of incident.
While it wasn't immediately clear how long the unidentified attendant remained in the hospital, a letter from her mother published Monday in the Gazette said the woman spent time at St. Vincent Healthcare and the New Hope Rehabilitation Center.
A final NTSB report on the event could take months to complete as investigators comb through interviews and other details from the flight.
Information from: The Billings Gazette, http://www.billingsgazette.com