A missing external panel on a Boeing plane was detected when it landed at an airport in the US state of Oregon on Friday, says United Airlines.
A spokesperson said United flight 433, from San Francisco, arrived at the Rogue Valley International Airport in Medford, Oregon, at about 11:30 (18:30 GMT) on Friday.
The 25-year-old Boeing 737-800 was carrying 139 passengers and 6 crew.
No-one was injured – the missing panel went unnoticed during the flight.
Boeing is under fierce scrutiny after a series of high-profile safety incidents.
Amber Judd, a senior official at Rogue Valley International Medford Airport, said the plane landed safely and the external panel was only discovered missing during a post-flight inspection.
“We’ll conduct a thorough examination of the plane and perform all the needed repairs before it returns to service,” she said.
An investigation would be carried out “to better better understand how this damage occurred”, she added.
The missing panel was next to the landing gear, on the underside of the aircraft, according to images of the aircraft on social media. All outgoing and incoming flights were paused at the airport to search for debris, none was found.
The US Federal Aviation Authority (FAA) said it was investigating how the panel came apart.
Boeing came under renewed scrutiny after a January incident involving a Boeing 737 Max 9 – part of a new range of planes to succeed older 737s – saw an unused cabin door blow out a few minutes after take-off in January.
The incident onboard Alaska Airlines flight 1282 left a gaping hole in the side of the plane and forced an emergency landing.
