Image copyright San Jose Police Image caption Police arrested Michael Kellar and Gail Burnworth after a plane passenger spotted text messages

A nursery school teacher has been called a "hero" after she spotted a plane passenger allegedly sending text messages discussing child sexual abuse.

The woman, who has not been named, was able to read the messages of the man in front of her on the Seattle-San Jose flight because they were in a large font on a large smart phone.

She took pictures of the screen and informed airline staff, police say.

It led to the arrests of Michael Kellar, and later Gail Burnworth.

Two children, aged five and seven, have been identified as the alleged victims.

Southwest Airlines employees alerted police to the texts. After landing at Mineta San Jose International Airport, in California, Mr Kellar was detained on the spot.

But Detective Sergeant Brian Spears of San Jose Police stressed that, without the teacher's decision to act, "he would have been lost".

"I let her know, right off the bat, that she is my hero," he told reporters.

Image copyright AFP Image caption Mr Kellar was travelling from Seattle to San Jose

He told NBC Bay Area: "If it wasn't for that young lady's actions, another sexual assault would have occurred."

Det Sgt Spears added it was worrying Mr Kellar had "seemed so nonchalant" about the messages he was sending that he had not even noticed the woman taking photographs.

"It was close to advertising the conversation," he said.

According to MercuryNews.com, Mr Kellar reportedly said the messages were just fantasy, but further investigation led police to Ms Burnworth, who is understood to have been dating him for about a year.

They also identified two alleged victims.

Mr Kellar, 56, of Tacoma, Washington State, was arrested on suspicion of two counts of attempted child molestation and two counts of solicitation of a sex crime, San Jose Police said.

Ms Burnworth, 50, also of Tacoma, was arrested on charges of sexual exploitation of a minor, rape of a child and dealing in depictions of a minor engaged in sexually explicit conduct.