Investigators say a broken part prevented pilots of a Delta plane from lowering the nose landing gear before landing last month in Charlotte, North Carolina.

The National Transportation Safety Board said Tuesday that it sent the fractured part, called a lock link, to its laboratory for examination as it investigates the June 28 incident.

The NTSB said when the upper lock link broke, it allowed the lower lock link to swing down and prevent the landing gear assembly from moving.

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Maintenance records for the Boeing 717 have been "quarantined and will be subject to review," the NTSB said. The plane was built in 2000, according to Federal Aviation Administration records.

The NTSB said the pilots of the flight from Atlanta tried several times to lower the landing gear while they circled the Charlotte airport twice to trouble-shoot the problem. Air traffic controllers told the crew they couldn't see the nose wheel.

The pilots were able to land the plane safely, sliding to a stop on the runway. There were no reports of injuries among the 99 passengers and five crew members, who evacuated on slides, but the plane sustained substantial damage.