Sooner or later some trigger happy fighter pilot is going to shoot down a civilian plane that is at the wrong place at the wrong time.

DENVER - The military sent dozens of fighter jets Wednesday to patrol the skies over New York, Washington and other U.S. and Canadian cities minutes after a small plane crashed into a New York City high-rise.

Adm. Timothy Keating, commander of U.S. Northern Command, told the Associated Press that military officials knew it was probably not a terrorist act "about a half an hour after it happened."

"This is a significant event," he later said at a news conference. "My first reaction when I saw an airplane going into a building in New York City was, 'Oh no, we've got another 9/11.' "

Officials said the single-engine plane, carrying New York Yankee Cory Lidle, slammed into a skyscraper, killing the pitcher and a second person.

About 2 1/2 hours after the incident, many of the military aircraft were still aloft, some of them being refueled by tankers, Keating said. He said cities covered also included Los Angeles and Seattle.

Keating said he ordered the fighters to be scrambled immediately after seeing information about the crash on television. The aircraft "were in the air in less than 10 minutes," he said, adding, "We assumed it was (a terrorist act) until we were confident it wasn't."

"The fact we were able to have dozens of fighters airborne in a very brief period of time ... sends a message to the terrorists that we're ready to respond."

The North American Aerospace Defense Command said that the patrols would continue for some time and that the fighters then would remain on high alert. NORAD would not provide details on the flights.

The military would not say exactly how many fighters were on patrol or identify exactly which cities had fighters circling the skies, citing security reasons.

In addition to the fighters, the military sent up other support aircraft, including Airborne Warning and Control System and tankers. AWACS planes are used to coordinate the flights of the fighters and to track any other aircraft in the area.

U.S. Northern Command was created after the Sept. 11, 2001, terrorist attacks to ensure that the military is prepared for security threats inside U.S. borders.