Hundreds of lawyers and staff at Sidley Austin and Willkie Farr & Gallagher returned to their Manhattan offices Thursday, three days after a helicopter crash-landed on the roof of the firms' building, forcing an evacuation.

Both firms had been working outside their offices at 787 Seventh Ave. since Monday afternoon, when the crash occurred. Authorities were investigating the incident and its impact on the building, preventing tenants from returning the building Tuesday and Wednesday. The New York Fire Department said a fire broke out on the roof after the Monday crash, which killed the helicopter's pilot.

During the two-and -a-half-day absence from the building, Sidley's lawyers worked remotely. Some of Willkie's lawyers worked from a client's offices, while others worked from home, co-chairman Steven Gartner told ALM on Tuesday. By Wednesday night, however, the building's management gave the all-clear.

“We have received confirmation from the landlord at 787 Seventh Avenue that we are clear to return to our office space tomorrow beginning at 7 a.m.,” a Willkie spokeswoman said Wednesday evening.

Samir Gandhi, the managing partner of Sidley's New York office, told ALM on Thursday that lawyers and staff are back to their routines in their office, but “I wouldn't say we're back to normal,” he said, because the event was unsettling.

“This wasn't a snow day, it was an unusual event,” he said. “We're walking the floors to make sure people are doing well and integrated.”

Sidley occupies about 11 floors in the building. None of Sidley's systems or office resources were affected, he said. “People were able to access (systems) remotely,” he said, noting the only disruption came from leaving personal items or laptops in the office during the evacuation.

There was no interruption in handling client matters during the office absence, he added.

Lawyers, bankers and other white-collar professionals who fill the building said the floor shook from the impact of the helicopter Monday afternoon. Minutes later, they heard an announcement over the intercom, instructing an evacuation.

The crash-landing, which took place amid light rain and heavy fog that wrapped around the top of the 700-foot building, brought dozens of fire trucks, police vehicles and ambulances to the building Monday. The National Transportation Safety Board is still investigating the crash and its cause, according to a spokesperson for the agency.