A New Jersey man allegedly sexually abused a woman on a long-haul flight and then wrote her a note that said, "I was stupid."

Ganesh Parkar, 40, had a seat in business class for a Dec. 21 Air India flight from Mumbai, India, to Newark, New Jersey, but before takeoff he moved to a seat near a woman in economy class, authorities said.

Although the row was not full, he moved to a seat right next to the woman after takeoff, according to a criminal complaint filed in federal court.

Air India planes are parked on the tarmac at the Terminal 3 of Indira Gandhi International Airport in New Delhi, India. Kevin Frayer / AP

She fell asleep and awoke to find a blanket she had placed over her had been pulled down. She pulled it back up and fell asleep again — waking up to find the blanket off and Parkar's hand inside her shirt, court papers allege.

"What the hell are you doing?" she yelled, then got up and told a flight attendant what happened.

Parkar allegedly followed the woman until ordered to return to business class. He then made repeated requests to speak with the victim, authorities said.

"During the remainder of the flight, defendant Parkar wrote two short notes to the victim in which he, in sum and substance, apologized for a 'moment's stupidity' and stated, 'I acknowledged I was stupid,'" an FBI agent wrote in the complaint.

Parkar was due to appear in federal court Thursday afternoon. He faces up to two years in prison and a $250,000 fine if convicted.

The FBI said there is no comprehensive data about how often plane passengers are sexually attacked because many incidents are not reported to law-enforcement. In 2015, the bureau opened 40 cases, and it had opened 58 cases between January and September 2016.

An FBI spokesperson said victims of in-flight sexual harassment or abuse are encouraged to report incidents to police or the bureau.