NEW YORK (AP) A change to the design of a needle that will sit atop One World Trade Center is raising questions over whether the building will still be America’s tallest when completed.

The 408-ft. (124-m) needle will no longer be enclosed in a fiberglass-and-steel enclosure called a radome, a feature that was recently removed from the original design because the building’s developer said it would be impossible to properly maintain or repair it.

Without the enclosure, it’s unclear whether the needle is an antenna or a spire — a crucial distinction in terms of measuring the building’s height. Without the spire, One World Trade Center would actually be shorter than the Willis Tower in Chicago, which currently wears the crown of tallest building in the United States at 1,451 ft. (442 m), not including its own antennas.

The skyscraper recently became New York City’s tallest building as workers erected steel columns that were just high enough to rise above the Empire State Building’s observation deck. The building is being constructed to replace the twin towers destroyed in the Sept. 11, 2001, terror attacks.

In order to repair or replace a broken panel on the needle’s proposed enclosure, a climber would have to scale the spire, attach a cable to the top, lower the cable about 2,000 ft. (610 m) down, and then use it to hoist a 2,000-lb. (907-km) piece of fiberglass back to the top, said Jordan Barowitz, a spokesman of Douglas Durst, the building’s developer.

“This is the stuff of ’Mission Impossible,’ not skyscraper construction,” Barowitz said.

The tower’s architects at Skidmore Owings & Merrill LLP did not immediately respond to a request for comment May 10.

Designs call for the tower’s roof to stand at 1,368 ft. (416.97 m) — the same height as the north tower of the original World Trade Center. With the needle, the building’s total height will be a symbolic 1,776 ft. (541 m), referring to America’s founding in 1776.

Experts and architects have long disagreed about how to measure the height of skyscrapers that have masts, spires and antennas that stretch into the sky.

The Council on Tall Buildings and Urban Habitat, a Chicago-based organization considered an authority on such records, said antennas do not count when determining building height.

An antenna, the group said, is something simply added to the top of a tower that can be removed. By contrast, a spire is something that is part of the building’s architectural design.

The council has not yet decided how the needle’s lack of an enclosure will affect its status as either an antenna or a spire, though it will, indeed, function as a broadcast antenna. On its Web site, the Port Authority of New York and New Jersey describes the needle as an antenna.

“The short answer is we don’t know yet,” said Kevin Brass, a spokesman of the council. “There is no doubt that this change will raise questions about the height.”

The council’s committee on building height will ultimately have to sit down with updated drawings from the architects and developers and make a final determination, Brass said.

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