WASHINGTON » Federal safety officials urge parents to put their children in child seat on planes, but a California mother says that twice in the last month she has been thwarted by airlines when she tried to do the right thing.

Melissa Bradley, 39, said she was forced off a United Airlines flight at San Francisco International Airport on Wednesday in a dispute over an economy-class row too narrow to accommodate an infant carrier for her 1-year-old daughter. Bradley was involved in a similar incident two days before Christmas on a Skywest flight from Aspen, Colo., to San Francisco, although she wasn’t asked to leave the plane in that instance.

Bradley, who has three older children, said she has been using infant and child seats on planes for years without a hitch until the recent incidents. She said she buys separate seats for her children because she worries that she won’t be able to hold them in her lap if the plane encounters turbulence.

National Transportation Safety Board Chairman Deborah Hersman has been campaigning for regulations that would require all infants and young children be secured in child seats on planes rather than allowed to fly in a parent’s lap. She has said that children deserve the same safety protections as seat-belted adults.

A Transportation Department aviation advisory panel recommended last month that the Federal Aviation Administration conduct a new study of the issue. Glen Tilton, chairman of United’s parent company, UAL Corp., was a member of the panel.

United spokesman Rahsaan Johnson said Bradley and her traveling party were removed from Flight 75 to Honolulu on Wednesday because she was causing a disruption by taking pictures.

Bradley said she took a picture of the narrow row because an FAA inspector with whom she spoke after the Skywest incident had asked her if she had a picture. She denied that she was disruptive.

Bradley, who owns a real estate firm in Marin County, said she called a United customer service executive two weeks before the Honolulu flight to ask what she needed to do to make sure she’d be able to use the infant carrier. She said she was told to simply to let United employees know when she checked in, which she did. But when she boarded the Boeing 777, she discovered the rows in economy seating were too close together to accommodate the Graco Snug Ride infant carrier, which is approved for airline use.

Johnson acknowledged that the rows were too close together for the carrier, but he said Bradley couldn’t be moved to wider row because those seats were full.

United rebooked her, her family and their traveling companions on a later flight to Honolulu, Bradley said. The rows were far enough apart on that plane to accommodate the carrier, she said.

"Honestly, this was the last thing I wanted to have happen on that plane," Bradley said. "I begged them to accommodate me."