The Federal Aviation Administration said it’s conducting an investigation after a missing panel was discovered in a United Airlines Holding Inc. plane that landed Friday in Oregon.    

United Flight 433 departed from San Francisco International Airport and landed safely around 1:45 p.m. local time at Oregon’s Medford Airport. A post-landing inspection by the airline revealed a missing panel, according to the FAA. 

United said it will conduct a thorough examination of the plane, a Boeing Co. 737-800 aircraft, and perform repairs needed before it returns to service, according to a statement by the airline on Friday. The carrier pledged to conduct an investigation into how the damage occurred. There were 139 passengers and six crew members on board the flight. 

Airline safety has come under scrutiny since the Jan. 5 blowout of a Boeing 737 Max door plug. Still, the latest incident involves a different type of aircraft.