Editor's Note: This is the first of a series of reports examining the safety of the nation's nuclear facilities.

NEW YORK—In the weeks following Sept. 11, the Federal Aviation Administration issued a no-fly zone over all the country’s nuclear plants. But it is now legal to fly directly over plants as long as the plane maintains an altitude of 2,000 feet.

But will these relaxed regulations compromise security at nuclear plants against possible terror attacks from the sky?

Anti-nuclear activists say yes, and argue the plants are particularly vulnerable to an air attack similar to the World Trade Center and Pentagon strikes. But the nuclear industry insists that's not the case.

"We do not believe they are a good target at all for an air attack," said Steve Floyd of the Nuclear Energy Institute. "We think the problem of being able to hit the building in the right place combined with the robust design of the facility makes such an attack extremely improbable of causing a significant problem."

Fox News decided to check out the safety conditions aboard a four-seat Cessna airplane rented from a flight school in Teterboro, N.J.

The plan was to fly over the Indian Point Nuclear Power Plant, 40 miles up the Hudson River from the airport, and just 33 miles from New York City.

The plant appeared just 10 minutes after takeoff, on the right side of the plane. The aircraft crossed over the plant three times, for a full 20 minutes.

No one warned the pilot of anything. No one at the plant, in fact, did or said a single thing in regards to the plane.

The pilot, noting how close he was able to get to the domes, said it would not be difficult to steer the plane down and smash into the plant.

"You're not that high and they probably wouldn't be expecting it," he said. "It would probably be pretty easy."

Edwin Lyman, an official with the Nuclear Control Institute, a group that lobbies against the nuclear power industry, was put on edge by this test flight’s success. "That is a severe problem," he said.

Even a small plane could damage a nuclear power plant, he added, and "a small craft packed with explosives could add an even greater punch."

But Floyd didn’t seem as worried by the experiment.

"Given the robustness of the buildings, a small plane can't carry enough explosives to cause a significant problem structurally at a nuclear power plant," he said. "There's an average of somewhere between 12 to 15 feet of concrete and steel that an airplane would have to penetrate in order to cause a direct impact on the fuel that's in the reactor."

It would be almost impossible for even a large plane to get through, he explained.

But not all of a plant’s radioactive materials are kept in the reactor. Highly hazardous spent fuel rods are housed in the domes – often in what critics say are easily breached concrete encasements.

"Damage to the spent fuel pool could lead to a massive release of radioactivity, which would then threaten the entire New York metropolitan area if we're talking about Indian Point," Lyman said.

The foot print size of these spent fuel pools must also be examined, Floyd said. They are typically 40 feet by 60 feet. That's a very small target for an airplane traveling at 400 miles per hour to try to hit.

There are more than 103 nuclear plants in the country, and almost all are close to at least one major airport. That leaves some looking to the sky feeling queasy with a far more terrifying type of air sickness.

Fox News' Amy C. Sims contributed to this report.