NEW YORK (Reuters) – Investigators from the National Transportation Safety Board (NTSB) were sifting through the wreckage of a helicopter atop a Manhattan skyscraper on Tuesday as they sought to determine why the aircraft crashed on the roof a day earlier, killing the pilot.

Tim McCormack, the pilot, was the only person aboard when he crashed onto the roof of 787 Seventh Avenue with enough force to jolt workers at the finance and law firms inside the 50-floor tower in midtown Manhattan.

Emergency vehicles are seen outside 787 7th Avenue in midtown Manhattan where a helicopter crashed in New York City, New York, U.S., June 10, 2019. REUTERS/Mike Segar

Police and other officials believe it was an accident, but have yet to say why McCormack was flying over one of the country’s densest urban districts through rain and low clouds on Monday afternoon.

The crash stirred memories of the Sept. 11 attacks and sparked renewed calls for tightening restrictions for New York City’s airspace. U.S. Representative Carolyn Maloney, who represents parts of Manhattan, said she wanted all “nonessential” flights banned.

McCormack was an experienced pilot who had taken off from a heliport on Manhattan’s east side to head to Linden Airport in New Jersey, according to Paul Dudley, the airport’s director.

He would have needed clearance from the air traffic control tower at New York City’s LaGuardia Airport to fly over that part of Manhattan, but it was unclear if that happened, Mayor Bill de Blasio told reporters on Monday.

The Port Authority of New York & New Jersey, the state agency that manages the airport, did not respond to questions about the incident on Tuesday.

The Federal Aviation Administration said on Monday that controllers “did not handle” the flight, but it remained unclear whether there was any communication at all between the helicopter and air traffic authorities.

A spokesman for the NTSB, a federal agency that determines the causes of major transportation accidents, did not respond to questions on Tuesday about the status of the investigation.

The crash site is less than a half mile (0.8 km) from Trump Tower, where U.S. President Donald Trump maintains an apartment. The area has been under extra-tight flight restrictions since Trump’s election in 2016.

(Reporting by Jonathan Allen; Editing by Scott Malone and Bill Berkrot)