(Reuters) -Boeing is in the early stages of developing a new single-aisle airplane that would eventually replace the 737 MAX, the Wall Street Journal reported on Monday, citing people familiar with the matter. Boeing and Rolls-Royce did not immediately respond to a Reuters' request for comment. The 737 MAX entered service in 2017 but was grounded globally in 2019 after two fatal crashes killed 346 people. Last Friday, the FAA said it would allow the planemaker to issue airworthiness certificates for some 737 MAX jets, starting this week. In early 2024, the FAA imposed a production cap of 38 737 MAX planes per month after a mid-air cabin panel blowout on a new Alaska Airlines jet, which was later found to be missing four bolts.