A drunk and disruptive passenger who in May groped three women and caused a London-bound US Airways flight to return to Philadelphia pleaded guilty Wednesday in federal court to interference with a flight crew, a felony.

Robert John Coppack, 41, said he was now being treated for alcohol and drug addiction at a Philadelphia rehab facility. He wears an electronic ankle bracelet to monitor his whereabouts.

U.S. District Judge John Padova set sentencing for Dec. 16. The plea carries a maximum 20-year prison sentence.

Coppack stood solemnly in dark sweater, slacks, and sneakers. He told the judge he takes medications for depression and had been hospitalized several times in recent years for mental illness or narcotics addiction.

On May 13, Coppack, of LaVerne, Calif., was on US Airways Flight 728, seated next to an 18-year-old student traveling with a college program to London, Assistant U.S. Attorney Sarah Grieb said.

Coppack began inappropriately touching the student, Grieb said. He poked the arm of another woman across the aisle who told him to stop. Coppack used profanity and kept touching the student's arm and knee, even after she told him to stop, Grieb said.

He drank from a Gatorade bottle and said "he had alcohol in there. The student noticed alcohol on the defendant's breath," the prosecutor said.

A flight attendant summoned federal air marshals who were aboard, and Coppack was taken to the back of the plane. On his way, he stroked a third female passenger's arm and touched her breast, Grieb said.

Coppack told the air marshals "he'd had a little too much to drink and was just trying to get back to England." He has dual citizenship in the United States and United Kingdom.

Coppack pointed two fingers at the air marshals, used an obscenity, and threatened to hit them. He was handcuffed and officials decided to return the flight to Philadelphia. The plane took off again five hours late.

He continued to use "belligerent language and yell profanity," and, at one point, released and flung his seat belt, which "knocked an air marshal into the aisle," Grieb said.

Federal public defender Kathleen Gaughan told the judge, "It's not disputed that Mr. Coppack was extremely intoxicated and slurred his language."

As part of the plea, Coppack agreed to pay a fine and restitution.

"US Airways was putting together the restitution amount," Grieb said. "It was several hundred thousand dollars."