Boeing is tightening procedures on its 737 production line after foreign objects were discovered in the fuel tanks of several stored 737 MAX aircraft. The discovery, first reported by Leeham News, prompted a memo from 737 program general manager Mark Jenks to workers describing the situation as unacceptable. Foreign Object Debris, or FOD, refers to parts, tools or other objects left in the aircraft during the production process. Boeing has had a problem with this at its 787 facility in South Carolina and with its KC-46A tanker, the latter prompting the US Air Force to twice suspend deliveries. READ: Boeing moves to distribute second $US50m from MAX fund. Jenks said one FOD “escape” was one too many. “With your help and focus, we will eliminate FOD from our production system,’’ he said, adding meetings had already been held in the 737 production facility in Renton, Washington, to discuss new procedures. These include new instructions and checklists for those working in fuel cell areas and additional verifications in the tank closure process to ensure there is no FOD in fuel tanks. New signage will be also added to the appropriate work areas reminding workers about appropriate procedures. Boeing has suspended 737 MAX production but more than 400 undelivered aircraft are stored at various locations. The global MAX fleet was grounded after two fatal crashes which killed 346 people were linked to problems with flight control software known as MCAS. Boeing is inspecting the stored planes ahead of a decision by the US Federal Aviation Administration and other regulators to allow the aircraft to fly again. When that will happen remains unclear and is dependent on FAA flights to test changes to MCAS and a process to ratify new training requirements. There had been speculation the FAA test flights would take place in the next few weeks but US carriers have since removed the MAX from their schedules until at least August. One of the three US airlines operating the MAX, United Airlines, has dropped the MAX from its schedule until September 4. US reports said the FOD find was not expected to impact the return to service.