It's unusual for a co-pilot or captain to take over a plane that's landing when it's so close to the tarmac.
Sixteen people were injured in the July 22 hard landing, which the NTSB is still investigating.
The federal aviation agency on Tuesday issued an update report that offers a glimpse into what happened in the cockpit of the Boeing 737 minutes before its nose hit the tarmac and the landing gear collapsed, sending it skidding before it came to a halt in a grassy area.
"At this point in the investigation, no mechanical anomalies or malfunctions have been found," the NTSB said in its update. "A preliminary examination of the nose gear indicated that it failed due to stress overload."
Passengers quickly exited the plane using its emergency chutes. Of the 16 injured passengers, at least six were hospitalized for treatment.
In a statement Tuesday, the NTSB said that as the plane approached LaGuardia the captain had been monitoring the landing and suddenly took over from the plane's first officer. NTSB officials said the latest information was only "a factual update" and they could not answer further questions as the probe continues.
The agency said the captain has been at Dallas-based Southwest Airlines Inc.
The first officer has been with the airline for about a year and a half, flying a total of about 5,200 hours including 4,000 as pilot-in-command. He's logged about 1,100 hours in 737s, none of them as pilot-in-command.
The first officer had "previous operational experience" at LaGuardia, including six flights this year, the NTSB said. And the captain reported having flown into LaGuardia twice, including the accident flight, serving as the pilot monitoring for both flights.
Flight 345 from Nashville, Tenn., with 150 people aboard, was the pair's first trip together.
In a statement issued just after the accident, Southwest said the aircraft's nose gear had collapsed upon landing. It said last month that a nose-pointed-down landing described by investigators violated its normal procedures. It did not immediately respond to a call for comment on the latest NTSB report.
The names of the two pilots were not released.