(CNN) A new federal complaint describes lurid text messages between an airline passenger and a woman last month discussing performing sex acts on children and drugging the minors to facilitate the abuse, court papers show.

Michael Kellar, 56, and Gail Lynn Burnworth, 50, both of Tacoma, Washington, exchanged the flurry of text messages in July, including on the day Kellar was a passenger aboard a Seattle, Washington-to-San Jose, California, flight on July 31, according to the federal complaint.

A passenger sitting behind Kellar spotted the text messages, took photos of the conversation and alerted authorities. The couple was questioned and arrested

Kellar has been charged with attempted enticement of a minor and both face a charge of conspiracy to produce child pornography, according to the complaint unsealed Monday.

The complaint lays out the couple's plans to sexually abuse a 5-year-old and 7-year-old who lived with Burnworth, her ex-husband and his wife. Burnworth, who is not the children's mother, also promised to take graphic photos and videos at Kellar's request, the complaint said.

Among Kellar's requests were videos of molestation, bestiality, fetish behavior involving feces and "kids videos," the complaint said.

Authorities allege couple exchanged text messages.

In a July 28 exchange, Kellar asked Burnworth: "Do you really think you can do this or are you just saying this???" the complaint said.

Burnworth responded: "No I think I can do it if I don't have parents over my shoulder or worried about who's going to walk in on me. And then on Sunday I will have kids no parents, just kids," the complaint said.

Tipster says she's not a hero

Authorities were tipped off to the case by a plane passenger who was just trying to look out the window.

As the plane was descending, the woman leaned forward to look out the window in the row ahead of her, The San Jose Mercury News reported. But suddenly another passenger's phone obstructed her view.

"I don't know how I saw it, I just saw in big text, 'child in their underwear,'" the woman told The News. "I thought, 'What did I just see?' My heart started racing. Then I could see more texts coming in."

The woman is not being identified by the newspaper at her request due to safety and privacy concerns.

After seeing the alarming texts, "my instinct just told me to discreetly take some pictures," she said. "As he kept obsessively looking at the texts, I just decided to snap pictures of texts he was re-reading."

The woman said she then alerted a flight attendant, who then called police, The News reported.

"I'm being labeled as a hero. I don't need a bunch of attention. I'm just so thankful the kids are safe," the woman said, according to The News.

Suspects in custody

Kellar, who is in the Santa Clara County jail, is scheduled to appear Tuesday in a federal district court in San Jose. No information was immediately available on Kellar's defense attorney.

Burnworth appeared Monday before a magistrate in a Tacoma courtroom. She didn't make a statement in court other than acknowledging she understood the charges she faces. Burnworth has a detention hearing scheduled for Thursday.

She is being held in a federal detention center in Seattle. Burnworth's federal public defender, Jerome Kuh, did not return a phone call or an email to CNN on Monday.

The two young children, who were identified as victims, were safe, San Jose police said last week.

Couple first met on dating website

In a July 31 interview with Seattle police, Burnworth said she met Kellar on match.com about a year ago and she visited his home several times, the complaint said. Kellar is divorced with two children, the complaint said.

Burnworth told authorities she and Kellar had engaged in sexual intercourse and fetish behavior involving feces, recording several encounters, the complaint said.

Burnworth told police she "sexually assaulted and produced approximately ten depictions of child pornography" involving one child, the complaint said.

In all, Burnworth said she took photos and videos of "as many as fifteen to twenty depictions" involving the two minors and emailed them to Kellar, the complaint said.

A third minor also lived in the home, authorities said.

Burnworth told police Kellar had ultimately backed out on the arrangement before the appointed time, telling her, "Well, I'm not coming because I know you won't go through with this," the complaint said.

"Burnworth stated she did not even have access" to the two children at the time she and Kellar planned the encounter, the complaint said. She also told police that if she had the chance, she would have let Kellar have sexual intercourse with one of the children and doing so may have required drugging her, the complaint said.

Kellar, who was traveling on the Southwest Airlines flight for work, acknowledged he knew that Burnworth lived with three minors, two of whom he described as "young," the complaint said. But when confronted about specific references to abusing children, Kellar told police "he was engaged in fantasy," the complaint said.

Police retrieved the deleted messages between Kellar and Burnworth from Kellar's phone, the complaint said.

In another graphic exchange, also on July 28, Kellar allegedly texted: "Do you think you can knock them out enough with the Benadryl?"

Burnworth responded: "I don't know what we can sure give it a big try."

"Only if you think it will be safe!" Kellar responded, the complaint said.