Before the scheduled landing at Philadelphia, the crew got an indication that the landing gear was not down and did a flyover to confirm that the nose wheels had not deployed, airport spokeswoman Victoria Lupica said.
Fire crews spread foam on the runway as a precaution before the landing at about 9:20 a.m.
The plane skidded down the runway on its nose, but there was no smoke or fire, Lupica said. Passengers were taken to the terminal by bus.
The cause was being investigated, said US Airways spokesman Morgan Durrant. The Federal Aviation Administration and the National Transportation Safety Board also were investigating, Lupica said.
The airport had to be closed for about 25 minutes, Lupica said. It reported some flights delayed more than two hours around midday while the plane remained on one of the four runways. That runway reopened in the early afternoon, and most flights were running on time, Lupica said.