WASHINGTON — While the planning of Tuesday's terrorist attacks on the World Trade Center and the Pentagon was sophisticated, the flying skill necessary to plow three jetliners into two large public buildings is relatively commonplace and easy to acquire, aviation and security experts said.

A terrorist with modest piloting abilities could learn to fly these twin-engine airliners from sophisticated simulators readily available at commercial flight schools in the United States and abroad. Experts said two months of training at such facilities would cost $20,000 to $30,000.

"Whoever did this was at least an amateur pilot with some advanced training," said Frank Richey, dean of applied aviation sciences at Embry-Riddle Aeronautical University in Daytona Beach, Fla.

"You could take a guy who's a rudimentary pilot, put him through two months of training and get him acclimated to the cockpit of either aircraft. A pilot who already has time in an airliner, he's easier to transition."

Richey said flight manuals, training videos and other technical publications are readily available from Boeing, which has manufactured 767s and 757s — jetliners used in Tuesday's attacks — since the early 1980s.

The level of skill and knowledge necessary to pull off three aerial suicide missions isn't as great as that required of an aspiring airline captain, said Mel Burkart, a retired airline captain who is a professor of aviation science at St. Louis University.

The terrorist pilots made their task easier by avoiding takeoff, when airspeed and control settings are far more critical.

"They weren't going into suborbital flight as astronauts," Burkart said. "A pilot would be concerned about staying within the flight envelope of his aircraft, but a terrorist who wants to turn the plane into a missile wouldn't care as much about maintaining a certain airspeed or throttle setting. Once the airplane is airborne and en route, it's a relatively easy chore to steer and get it to go up and down."

Aviation experts say it's significant the hijackers seized two aeronautical cousins. The Boeing 757 and 767 are so similar in cockpit instrumentation and flying characteristics that the Federal Aviation Administration lets pilots fly either aircraft under a single flight certificate.

These shared technical qualities would make the selection and training of terrorist pilots simple, experts said.

And if the terrorists had flight time in another type of jetliner, training would have been even simpler and cheaper, Richey said. Increasingly realistic flight-simulation software programs that run on desktop computers, along with training videos and flight manuals from Boeing, may have been sufficient.

Pilot candidates would have to master the flight-management system, a computerized autopilot so sophisticated it is possible to program an entire flight, from takeoff to landing, and let the plane fly itself, Richey said.

They would have to know how to feed course corrections and navigational data into the system and how to turn it off and manually fly the plane.

The terrorist pilots also would need enough flying savvy to use flight instruments and navigational aids to bring their planes down from high altitude and guide them to their target cities. They knew how to switch off radar transponders that send coded information that identify individual aircraft to air traffic controllers. But these are easily acquired skills, Burkart said.

Of greater necessity was training on how to spot the intended targets while flying large and fast-moving aircraft and how to line up and hit those targets without flying past them. Training could be set up on a desktop flight simulator, Burkart said.