"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", Mark Jenks, the Vice President and General Manager of the 737 programme said as quoted by Leeham News on Tuesday.
CNBC said Boeing plans to investigate the foreign objects in the tanks and also inspect all undelivered MAX planes, adding that the discovery "won’t impact the plane’s return to service at this time".
Boeing continued to build some 400 MAX planes after the grounding, before halting production altogether last month.
The company’s fiscal results for 2019 showed that the MAX controversy was draining its finances, causing Boeing its first annual loss in 23 years.
The MAX has been grounded since March 2019 by the US Federal Aviation Authority after two fatal crashes that killed 346 people on board. Investigations into the crashes revealed errors in the functioning of the jet’s piloting system, lapses in Boeing’s safety standard procedures, and subsequent cover-ups by company officials.