PARIS, France — By the time Gregory Hendricks noticed his wife’s passport was missing during their Paris-bound flight from Washington Dulles International airport, it was already too late. After they arrived at Paris’ Charles De Gaulle airport, the Hendricks were escorted through a security checkpoint to board a return flight home.

The in-flight theft that Gregory Hendricks blames for ruining the surprise French vacation he gave his wife might be more common than you think. While no government agency or industry group keeps statistics on in-flight theft, it’s not hard to find examples of the crime.

Last month, five business-class passengers traveling from Tokyo on an overnight Air France flight to Paris woke to find 4,000 euros in cash and other currency missing. A police investigation is ongoing in that case.

In April, the son of television actress Cybill Shepherd is scheduled to stand trial for in-flight theft. Cyrus Shepherd-Oppenheim, 22, was arrested last month after passengers identified him as the person who stole cash, a digital camera and other items from the carry-on bags of fellow travelers during a flight from San Francisco to Philadelphia.

“There’s a false sense of security on a plane,” said Steven Frischling, a frequent flyer turned airline industry blogger, who has written about the subject. “People feel safe because they’re in a confined metal tube. What can happen?”

Once passengers disembark and the items are gone, there is little anyone can do. The Tokyo-Paris flight may have attracted attention because it involved a large sum and it occurred in a business-class cabin, which is generally smaller and thought to be safer.

Nevertheless, an Air France spokeswoman said, “Passengers bear the sole responsibility for baggage that is not checked-in.” The company maintained that such occurrences are “infinitesimal” when considering that the airline transports about 150,000 passengers on 1,700 flights daily.

Detectives in flights’ destination cities do follow up on cases and network with each other, according to Paul Sireci, the chief of police at Tampa International Airport. His department, for instance, generated seven in-flight theft reports in 2008, compared to 131 theft reports airport-wide.

“If you are a victim of a theft then one theft is a problem,” Sireci wrote in an email. “But considering the number of flights we have during the year, seven reports of theft is a very small occurrence.”

The incident involving the Tokyo passengers was covered by the media and likely will be forgotten in a few months. But for passengers who’ve experienced a similar inconvenience, it’s a lesson learned hard and remembered.

“I was kind of jaded in thinking that people who made that trip were pretty honest folks,” said Hendricks, 49, by telephone. Asked why, he said, “because of the price of the ticket.” Upon further reflection, he added, “Now, it might be why they can afford to fly.”

How they do it

Frischling said he has been in anonymous contact with thieves who make a living stealing at airports. “There is a definite method to doing this,” he said.

In-flight thieves, Frischling said, would be likely to check-in online 24 hours in advance, picking a seat toward the rear of the plane. They prefer aisle seats and may feign an injury so they’re allowed to board early. This way, they can observe who is putting what where and how into the overhead bins. Are fellow passengers placing the zipper side of a suitcase toward the back wall or not, allowing for easy access? Which bags have locks? Are laptops being stored overhead?

Or the culprit could be one’s seatmate, as Paula Patrice, a New-York based model and actress, suspected when $350 was missing from a wallet inside her large Louis Vuitton bag after she used the restroom during a flight. When she wasn’t able to produce $5 to pay the flight attendant for her beverage even though she knew it had been there just moments before, “I was conflicted, so I did nothing,” she wrote in an email. “It seemed like there was no good recourse.”

Patrice, a frequent traveler, didn’t want to cause a scene or accuse her seatmate without any firm evidence. “She didn’t take the wallet, so how does one identify cash?” said Patrice.

Hendricks said he remembered a man coming from the back of the plane and rummaging through the compartment above his seat. At the time, “I was thinking there is no room up there,” he said, but he did not say anything. Passengers are generally too polite to stare and reluctant to speak up, Frischling said.

Thieves are also rather specific about what they’re looking for: wallets, cell phones, compact cameras and other small electronics that can be sold on eBay or to a pawnshop, Frischling said. Passports are usually not their primary targets since doctoring them has become increasingly difficult.

Hendricks said that after informing the crew about the missing passport, he innocently thought passengers would be searched as they exited the plane. “I thought they would stop everyone before they got too far.” But all the flight attendants could do was search the cabin and apologize.

Lessons learned

“I’m a savvy sort of person,” said Tom Hayes, 59, an international labor expert. “I know how to look after myself.” But he distracted and tired last month on an American Airlines overnight flight from Chicago to Brussels, when his passport disappeared.

Hayes was seated in business class and allowed the flight attendant to hang up his jacket in a closet with his Irish passport inside. Normally, he said, he wouldn’t have left the passport in the jacket pocket.

Had he not been a “middle-aged white guy” with European Union citizenship, Hayes said, things might have turned out differently at the immigration counter in Belgium where he was allowed to enter the country. (A spokesman for the Brussels Airport immigration division said border police have the discretion to admit travelers into the country based on some proof of identity.)

“It’s not an issue I’ll be dealing with again,” Hayes said.

Patrice said she learned to “keep petty cash on hand separate from your travel stash.”

The Hendrickses learned a few valuable lessons too. Since the incident in late 2006, they have kept their passports “in one of those carriers that go around your neck and down your shirt." The travel insurance they had so dutifully purchased did not protect them from in-flight theft. And calling the U.S. embassy in Paris on a Sunday for help to replace a stolen passport, Gregory Hendricks said, was “like getting a recording at a hospital” that said, “If this is an emergency, we’ll be open tomorrow.”