PORTLAND, Ore. >> A post-flight inspection revealed a missing panel on an older Boeing 737-800 that had just arrived at its destination in southern Oregon today after flying from San Francisco, officials said, the latest in a series of recent incidents involving aircraft manufactured by the company.

United Flight 433 left San Francisco at 10:20 a.m. and landed at Rogue Valley International-Medford Airport in Medford shortly before noon, according to FlightAware. The airport’s director, Amber Judd, said the plane landed safely without incident and the external panel was discovered missing during a post-flight inspection. No injuries were reported.

The airport paused operations to check the runway and airfield for debris, Judd said, and none was found.

Judd said she believed the United ground crew or pilots doing a routine inspection before the next flight were the ones who noticed the missing panel.

A United Airlines spokesperson said via email that the flight was carrying 139 passengers and six crew members, and no emergency was declared because there was no indication of the damage during the flight.

“After the aircraft was parked at the gate, it was discovered to be missing an external panel,” the United spokesperson said. “We’ll conduct a thorough examination of the plane and perform all the needed repairs before it returns to service. We’ll also conduct an investigation to better understand how this damage occurred.”

The Federal Aviation Administration also said it would investigate.

The missing panel was on the underside of the aircraft where the wing meets the body and just next to the landing gear, United said.

The plane made its first flight in April 1998 and was delivered to Continental Airlines in December of that year, according to the FAA. United Airlines has operated it since Nov. 30, 2011. It is a 737-824, part of the 737-800 series that was a precursor to the Max.

Boeing said, also via email, that it would defer comment to United about the carrier’s fleet and operations.

In January a panel that plugged a space left for an extra emergency door blew off a Boeing Max 9 jet in midair just minutes after an Alaska Airlines flight took off from Portland, leaving a gaping hole and forcing pilots to make an emergency landing. There were no serious injuries.

The door plug was eventually found in the backyard of a high school physics teacher in southwest Portland, along with other debris from the flight scattered nearby. The Department of Justice has launched a criminal investigation.

On March 6, fumes detected in the cabin of a Boeing 737-800 Alaska Airlines flight destined for Phoenix caused pilots to head back to the Portland airport.

The Port of Portland said passengers and crew noticed the fumes and the flight landed safely. Seven people including passengers and crew requested medical evaluations, but no one was hospitalized, officials said.