Massport objects to height of Winthrop Square skyscraper

MassPort says the 775-foot tower proposed for Winthrop Square will disrupt flight paths.HANDEL ARCHITECTS

Even as they deal with nearby residents worried about shadows on the ground, the developers of a skyscraper at Winthrop Square now face challenges up in the air, too.

The Massachusetts Port Authority, which operates Logan International Airport, said it strongly objects to the 775-foot height Millennium Partners has proposed at Winthrop Square, according to a letter to state environmental regulators released Wednesday.

A tower that tall, a Massport official wrote, would interfere with operations at Logan, blocking a popular takeoff corridor and probably leading to more noisy air traffic over Boston’s northern and western suburbs. Massport would object to anything taller than 710 feet on the site, which sits about two miles west of the airport.

Aviation height limits have long put a lid on super-tall development in downtown Boston, and similar concerns a decade ago helped scuttle plans to put a 1,000-foot tower on the Winthrop Square site, which now houses a shuttered city garage.

In its successful bid last year to develop the site — which it would buy from the city for $153 million — Millennium Partners pitched a 750-foot tower, despite advice from the Boston Planning & Development Agency that nothing taller than 725 was likely to pass muster with the airport. Then they filed a proposal that they said could reach “up to 775 feet.” Millennium’s top executive on the project did not respond to messages late Wednesday, but executive have suggested that they’re willing to be flexible on height.

In his letter, Massport deputy director Stewart Dalzell said the authority continues to talk with Millennium to ensure the project complies with height limits. A Massport spokesman declined to comment. In a letter outlining environmental review for the project, state Environmental Affairs Secretary Matthew Beaton urged Millennium to consider a 710-foot tower.

Cutting the tower by 65 feet would lop four or five stories off the 60-story tower, probably not a deal-killer for a project estimated to cost $1 billion. But that could reduce the city’s payday. Under Millennium’s deal with the BPDA, $50.8 million of the $152.8 million purchase price is tied to the sale of condos in the tower. Fewer floors could mean fewer condos, which could mean less cash for the city.

But it would have one side benefit that might placate opponents worried about shadows the tower would cast on Boston Common and the Public Garden: A shorter tower means shorter shadows.