United Airlines said Friday that one of its Boeing 737-800 aircraft discovered a missing exterior panel after landing safely at its intended destination at Rogue Valley International Medford Airport in Oregon.

United said the missing panel was discovered after the plane, which was carrying 139 passengers and six crew members, stopped at the gate.

“We will conduct a thorough inspection of the aircraft and make all necessary repairs before returning it to service,” the airline said in a statement, adding that an investigation would also be conducted to understand the cause of the accident.

Boeing had no comment and referred questions to United Airlines.

The plane took off from San Francisco, according to flight tracking website FlightRadar24.

The National Transportation Safety Board and the Federal Aviation Administration are investigating after a Boeing 737 MAX plane operated by United Airlines slid onto the grass and overran the runway at Houston’s George Bush Airport last week.

Boeing has been under intense regulatory scrutiny and investigations into safety and quality standards in the company’s production processes following the Jan. 5 Alaska Airlines in-flight panel explosion.