Paris Hilton's youngest brother was charged Tuesday with interfering with a flight crew on a trip from London during which authorities say he called other passengers peasants and made children cry with his death threats and profane tirades.

Conrad Hilton, 20, wearing a dark suit and shirt buttoned to the collar, shuffled into U.S. District Court in ankle chains with his hands manacled at his waist. A judge asked if he understood his rights and the charge, which was filed Monday and could carry a prison term of up to 20 years if Hilton is convicted.

"Yes, your honour," he repeated after each question, but he didn't enter a plea. He was released on a $100,000 unsecured bond, ordered to appear for arraignment March 5 and told to continue mental health treatment.

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Hilton's trouble on British Airways began moments after Flight 269 left the ground July 31. It continued for almost the entire 10 1/2-hour flight, according to a 17-page affidavit by FBI agent David Gates.

Hilton ignored instructions to keep his seat belt fastened and began pacing the aisle as the aircraft ascended, the document said. He complained that another passenger was giving him the "stink eye."

When told to return to his seat, he became unruly, and in a series of tirades, he threatened to kill several flight attendants and a co-pilot, and threatened to get them fired, the affidavit said.

"I could get you all fired in five minutes. I know your boss," Hilton said in one of the document's few quotes that didn't include an expletive. "My father will pay this out, he has done it before. Dad paid $300,000 last time."

Hilton's parents are socialite Kathy Hilton and businessman Rick Hilton, the grandson of the Hilton hotels founder whose name was also Conrad Hilton.

Defence lawyer Robert Shapiro, a friend of the Hilton family, said he had just received the documents and would have to review them with his client before making a statement on the case.

"It may be the effects of a sleeping pill" or something else, Shapiro said outside court.

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The FBI affidavit says Hilton threw a punch inches from another flight attendant's head that struck the bulkhead. Although the attendant, identified only by the initials O.P., said he felt threatened, he said, "I don't believe he intentionally wanted to hurt me."

A co-pilot who was assigned by the captain to look after Hilton noted that he appeared to be uncoordinated, delusional and paranoid.

Hilton said he was angry over the breakup with a girlfriend and wanted to smoke marijuana. At one point, he went to a lower deck restroom and the odour of pot wafted out, the affidavit said.

When confronted by the co-pilot, Hilton ran to an upper-deck restroom and smoked a cigarette, the document said. A paper towel was found wadded in the smoke detector.

Hilton eventually fell asleep and was handcuffed to his seat for the remaining 90 minutes of flight.

After landing in Los Angeles, Hilton told Gates, the FBI agent, he was returning from Greece and had taken a sleeping pill in London.

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According to the affidavit, Hilton acknowledged calling other passengers "peasants" and said he had would have killed one flight attendant if another passenger hadn't calmed him down.

"A hundred per cent I would have killed him," Hilton said.

When asked if he was serious, Hilton told Gates, "No, but I would have knocked him the [expletive] out."