San Jose police say the woman allegedly saw a man texting about sexually molesting children.
“The conversations were very particular in regards to sex acts that were to be performed on ... children,” a San Jose police spokesman said, news.com.au reports.
The female passenger photographed the man’s texts and informed the cabin crew. The man has been named as 56-year-old Michael Kellar.
Kellar told police that the texts were just a sexual fantasy game.
As CNN reports, detectives later inspected the man’s phone and found he had allegedly texted Gail Burnworth, in Tacoma, Washington.
Seattle police said the messaged contained “information that the woman had access to the children either as a caregiver or a babysitter”.
A five-year-old and seven-year-old were found in the woman’s care.
As The New York Times reports, Kellar has been booked with two counts of attempted child molestation and two counts of solicitation of a sex crime.
Burnworth was arrested, not formally charged, and then released in Tacoma. She was arrested on Friday for conspiracy to produce child pornography.
San Jose Police Sgt. Brian Spears told CNN that the actions of the female passenger were incredible heroic.
"I'd like to highlight that if it wasn't for this particular passenger taking action to alert the staff and alert the police, this catastrophic event would have been horrific," he said.