Boeing's 737 Max 8 planes have been hit with another complication as foreign object debris was found in the fuel tanks of some of the planes.
The company has reported the problem to the Federal Aviation Authority and each plane in the 400-strong fleet is now being inspected individually.
Foreign object debris (FOD) refers to equipment such as tools or rags.
Specialist aviation publication
Leeham News first reported the issue.
In a statement, Mark Jenks, the VP and GM of the 737 Program, said: "During these challenging times, our customers and the flying public are counting on us to do our best work each and every day. That’s why we’re taking action after a range of Foreign Object Debris (FOD) was recently found in the fuel tanks of several 737 MAX airplanes in storage.
"FOD is absolutely unacceptable. One escape is one too many. With your help and focus, we will eliminate FOD from our production system."
Last year, the Irish Aviation Authority suspended all Boeing 737 Max 8 to and from the country, after one Irish citizen was among 157 people killed when a flight from Ethiopia to Kenya crashed after just six minutes in the air.
Boeing eventually grounded the airliner entirely. The latest issue is unrelated to the sensor problems that are believed to have contributed to two fatal crashes last year.
