Passengers smoke on U.S. jetliners at least twice a week, according to authorities, breaking the law without creating an international incident.

WASHINGTON — Passengers smoke on U.S. jetliners at least twice a week, according to authorities, breaking the law without creating an international incident like an episode last week.

The Federal Aviation Administration (FAA) has brought 696 cases, some for civil fines of thousands of dollars, against people caught smoking aboard airliners in the past five years, said Diane Spitaliere, an agency spokeswoman. Lighting a cigarette on a plane has been banned for 20 years.

Carriers don’t have data on how often passengers attempt to smoke, though “these events still do happen,” said David Castelveter, a spokesman for the Air Transport Association trade group in Washington.

The implications of trying to light a cigarette onboard were brought into focus April 7, when a diplomat from Qatar allegedly attempted to do so on a United Airlines flight.

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Mohammed Al-Madadi, who helps manage the Qatar embassy in Washington, was smoking in the lavatory, said a law-enforcement official, speaking on condition of anonymity. When a flight attendant confronted him, he said he burned plastic on his sandal to mask the smell, the official said.

The comments were interpreted as threatening, and two fighter jets were scrambled to escort the United flight to Denver.

Al-Madadi was released from custody Sunday, said Alison Bradley, a spokeswoman for the embassy. The diplomat is going back to Qatar, a U.S. official said.

The smoking ban took effect in 1990 aboard U.S. flights, and the agency extended it to international trips starting in 1996, said Laura Brown, an FAA spokeswoman.

“It helped our business,” as both nonsmoking and smoking passengers said they appreciated the clearer cabin air, said Douglas Laird, former security chief at Northwest Airlines, now part of Delta.

Smoke detectors, which the FAA requires in all aircraft lavatories, alert flight crews to would-be violators. Even that doesn’t stop all would-be violators, said John Eakin, whose Air Data Research in Helotes, Texas, collects air-safety data.