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The helicopter lifted off in rain and fog and raced down the East River. But within minutes, the pilot was trying to return to the heliport he had just left.
The pilot, an experienced flier named Timothy McCormack, told the heliport he could not find his way.
“McCormack then stated that he did not know where he was,” a law enforcement official said on Tuesday.
That was Mr. McCormack’s last communication before he crashed and died on the roof of a 51-story office tower in the middle of Manhattan on Monday afternoon, the official said.
Now investigators will try to figure out why Mr. McCormack went astray in the 11 minutes after he took off, bound for an airport in New Jersey.
A team of investigators from the National Transportation Safety Board arrived on Monday night to begin piecing together the scary sequence that for brief moments had New Yorkers fearing another terrorist attack on their city. Police officials said they quickly ruled out that possibility.
The investigators may not have much to work with. The helicopter, a twin engine Agusta A109E, slammed so hard into the roof of the building, at 787 Seventh Avenue, that the aircraft was almost completely destroyed.
People who knew Mr. McCormack said he was intimately familiar with the skies over New York and had flown around the city for years, largely without incident.
Several years ago, he had calmly landed a helicopter full of passengers after a bird crashed into the windshield, a former employer recalled.
Just two hours before the crash, Mr. McCormack had dropped off a regular passenger, Daniele Bodini, at the city-owned heliport at the east end of 34th Street along the East River, the law-enforcement official said.
A worker there said Mr. McCormack had waited out the bad weather for two hours before he decided to head to the airport in Linden, N.J., where he usually parked the helicopter.
Mr. Bodini, the founder and chairman emeritus of American Continental Properties, a real estate company, used the helicopter to commute to the city from a home in upstate New York’s Hudson Valley. Mr. McCormack, who also lived upstate, had flown for Mr. Bodini’s company for five years, a company spokesman said.
Seeing a break in the weather, Mr. McCormack lifted off at 1:32 p.m., the law enforcement official said. Five minutes later, he was on the radio, saying he was turning around and asking for a landing spot, the official said.
His helicopter was spotted swooping up and down in an erratic fashion over the river. Instead of landing at the heliport, he headed inland over Midtown into some of the most tightly controlled airspace in the country.
At 1:43 p.m., a caller who works in an office of the Bank of Tokyo made the first 911 call about the crash, the law enforcement official said.
The caller reported that an aircraft had crashed on top of a building between 51st and 52nd Streets. Firefighters raced to the rooftop and extinguished the fire triggered by the crash.
Nobody, other than Mr. McCormack, was injured in the crash.