A United Airlines-operated Boeing 737-800 was missing an external panel when it landed in Medford, Oregon, on Friday, the airline said in a statement.

No injuries were reported, no emergency was declared, and there was no indication of a problem during the flight. The Federal Aviation Administration said it’s investigating.

Details about the missing panel were not provided.

The plane is a relative of a Boeing aircraft, the 737 Max 9, that lost a door plug in flight in January, but it is not the same model.

Friday’s late-morning flight started as scheduled in San Francisco en route to Medford and landed 17 minutes early, according to flight tracker FlightAware.com.

The aircraft was scheduled to be used for a subsequent flight to Denver, NBC affiliate KOBI of Medford reported, but that flight has been delayed.

Medford airport personnel searched the grounds unsuccessfully for the missing panel, the station said.

There were 139 passengers and six crew members on board.

“We’ll conduct a thorough examination of the plane and perform all the needed repairs before it returns to service,” United said in its statement Friday afternoon. “We’ll also conduct an investigation to better understand how this damage occurred.”

In January, a door plug detached from a 737 Max 9, and the cabin was subjected to rapid decompression that sucked debris out of the cabin, federal officials said. No serious injuries were reported.

That flight from Portland, Oregon, to San Bernardino County, California returned to Portland for an emergency landing, and the incident resulted in a temporary grounding of all U.S.-based 737 Max 9s, multiple lawsuits. In a preliminary finding, federal investigators determined the door plug lacked necessary retaining bolts.

The dummy panel is used in place of an emergency exit where one is unneeded because the aircraft has been configured for a passenger capacity below the number that would trigger more mandatory exits.