Many of the nation's flight instructors are focusing on ways to screen would-be pilots after a Florida teen-ager commandeered a plane and crashed into a skyscraper.

Charles J. Bishop of Palm Harbor, Fla., was killed Saturday after the four-seat plane crashed into the 28th floor of a 42-story Tampa skyscraper.

The 15-year-old was supposed to be performing a preflight check on the 2000 Cessna 172R as his flight instructor had requested, but instead took off without permission, police said. No one inside the building was injured.

Bishop's death — after hijackers crashed planes into New York's World Trade Center and the Pentagon last Sept. 11 — has sparked concerns about possible security gaps for those who fly small aircraft.

"You don't know how an individual's mind is going to work," said Joe Siligato, owner of Spirit Mountain Aviation, a flight school and charter service in Cody, Wyo.

Tampa Police Chief Bennie Holder said Sunday that Bishop left a note expressing support for terrorism leader Osama bin Laden, suggested he crashed the plane on purpose and said he acted alone. Holder said there was no indication Bishop specifically targeted the building or "had any intention of harming anyone else."

Some flight schools reacted immediately to the new threat. Greg Russell, general manager of CSG Aviation Services in Columbus, Ga., said he plans to convene his employees Monday to review security procedures.

"We've already made some drastic changes since September 11 and we'll probably make sure we do a little more now," Russell said.

Andy Dutzi, director of The Flight School at Palm Springs, Calif., said he has a 15-year-old student, and in light of the Tampa crash he intends to talk to teachers or counselors at the boy's school to ask about his state of mind.

Dutzi said his school requires flight instructors to be present with student pilots during preflight checks, but not all of them follow that order. He said fired a flight instructor six weeks ago for repeatedly ignoring the rule.

Most instructors said there was little they could do to prevent a similar situation, where instructors have gotten to know and trust a student.

Don Stanton, chief instructor at Sky Harbor Air Service in Cheyenne, Wyo., said nothing guarantees a student won't have mayhem in mind, but a mentor should be aware of the possibility. "Probably the biggest factor would be getting a handle on their personality," he said.

"What the flight instructor did was what normally happens," said Warren Morningstar, vice president of communications for the Aircraft Owners and Pilots Association. "There really was not a security breach. There was an abuse of trust here."

An instructor typically accompanies a student for the equipment check during the initial lessons but eventually, it is routine at many schools for novice pilots to do the preflight check alone.

"Everybody does that. How many times have you heard of people taking them and flying into buildings?" said Andy Surratt, owner of PilotMakers in West Chicago, Ill.

The Florida incident was a reminder for Bruce Smith, dean of the John D. Odegard School of Aerospace Sciences at the University of North Dakota. One of the school's instructors was killed in October 2000 after crashing a twin-engine plane on a runway in an apparent suicide.

Smith said his school now requires badges to get to airplanes and is working on requiring a hand or thumb print as well.

But even the new security measures aren't certain to prevent a repeat occurrence, he said.

"If they really are truly dedicated to doing this and they're secretive about it," Smith said, "there's not a lot you can do."