Over the last four years, the number of cases of sexual assault on aircraft being investigated by the F.B.I. has grown by about 30 percent as the public conversation about the problem has widened. The authorities anticipate that even more reports will emerge as pressure mounts for the airline industry to address assaults, and as cases like the ones announced on Thursday draw attention.

In recent months, at least three airlines, Alaska, United and Spirit, have announced new policies and efforts to keep passengers and crews safe, but many other airlines have been silent.

One of the criminal cases filed on Thursday involved an Alaska Airlines flight from Anchorage to Seattle in early March. During the flight, a woman, 22, was sitting in a window seat, with an empty seat between her and a man on the aisle. The man moved closer, began asking personal questions and tried to hold her hand, court documents said. The behavior escalated, according to the documents, as the man repeatedly grabbed the woman’s breasts and thighs, even as she told him, again and again, to stop.

The authorities charged Nicholas Matthew Stevens, 37, of Anchorage, with abusive sexual contact aboard an aircraft. A call to the federal public defender’s office in Anchorage, which is representing Mr. Stevens, was not returned by late Thursday. According to the prosecution’s documents, he told investigators that he had been drinking and had touched a female passenger during the flight, but that she had also touched him.

The second case involved a Norwegian Airlines flight from London to Seattle in January, in which a woman said she spent hours fending off another passenger. The woman, in her early 20s, said she then fell asleep and awoke to find the man’s hand inside her underwear, touching her vagina, and with her hand placed on his erect penis, according to court documents.