United flight from San Francisco missing external panel after landing in Oregon

A United Airlines plane that departed Friday from San Francisco International Airport was missing an external panel when it landed at its destination in Medford, Oregon.

United released the following statement:

"This afternoon, United flight 433 landed safely at its scheduled destination at Rogue Valley International/Medford Airport. After the aircraft was parked at the gate, it was discovered to be missing an external panel. 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."

United said the Boeing 737-800 had 139 passengers onboard the plane, with six crew members. The plane also did not declare an emergency while en route to Medford "as there was no indication of the damage during the flight," United said.

According to officials with the Rogue Valley International Medford Airport, the flight tower was immediately closed flight operations while maintenance crews swept the runways to make sure they were clear.

"We didn't find any debris or any panels or anything. So, it was reopened and everybody landed and operations continued normally,” said Amber Judd, director of Rogue Valley International Medford Airport in Oregon.

The incident involving United Airlines flight 433 is the latest in a string of recent mechanical problems on United airplanes.

On Thursday, United Airlines flight 1816 took off from Dallas-Fort Worth International Airport at 5:30 a.m. Just before landing in SFO at 7:30 a.m. local time, the United Airbus experienced a hydraulic leak. It was able to land safely, according to officials.

On Mar. 7, a Japan-bound United flight out of SFO was diverted to Los Angeles after a wheel fell off during takeoff.

Then on Mar. 8, in passengers had to be evacuated from a United Airlines plane in Houston after it rolled off a runway during landing and got stuck in the grass.

Also on Mar. 8, a United flight to Mexico City from SFO was diverted to LAX because of a hydraulics issue.

Last Monday, a United flight headed to SFO from Sydney, Australia had to turn around midflight after fluid was seen spewing out from the right rear landing gear.

All of the incidents are now under investigation and it has some aviation experts questioning their connection to the San Francisco airport.

"It keeps coming back to San Francisco and that’s my concern. This is a major maintenance base and a major hub for United and the issues seem to be San Francisco-centric," said Doug Rice, a retired pilot and aviation expert.

Mike McCarron, who is also an aviation expert, told NBC Bay Area on Friday that the large metal pieces are removed during maintenance on the Boeing 737’s engines. He added that they are supposed to be tightly screwed back into place before undergoing a final inspection to make sure they are reattached securely. McCarron stated that they are all areas for immediate concern for investigators.

“What they are going to do is look back at when that engine was last serviced, who did it and who inspected the work after it was done,” he said.

McCarron added United does much of their maintenance at SFO, where it employs 3,500 technicians. But he said that some U.S. airlines have turned to outsourcing work, something else for investigators to look into.

“More and more of the routine monthly or semi-annual inspections are being outsourced to third parties,” he said. “And some of these are out of the country and probably have less oversight than they would here in the United States.”

For now, United said the 737 in Friday’s incident will remain grounded while the airline makes repairs and investigates what went wrong before returning the aircraft to service.