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By Giulia Segreti
PARIS, June 20 (Reuters) - United Airlines has converted an order for 100 Boeing 737 MAX jets into one for the U.S. planemaker's new 737 MAX 10 model, the companies said at the Paris Airshow on Tuesday.
Boeing launched the new version of its best-selling 737 aircraft on Monday amid a flurry of deals.
United Airlines, which will become the largest single 737 MAX 10 customer in the world, said it expected the delivery of the first of the planes in late 2020.
Boeing Commercial Airplanes President and CEO Kevin McAllister said the order was an "endorsement" for the MAX 10.
Asked why the latest deal was a conversion a previous order, rather than a new one, United Airlines executive Gerry Laderman told Reuters: "We have a very healthy order book ... and it is very customary for us to place an order to have a certain timeline, and closer to the time we pick which model we want."
Laderman said that United Airlines already had a large MAX order, so there was no need for an incremental one.
He added the group had picked the MAX 10 model because it considered it to be "the one with the best economics of the family," in terms of seat per mile cost.
The executive said the U.S carrier had not finalised the seating configuration for the airplanes but that they would be used as domestic aircraft.
United also announced an order for four additional Boeing 777-300ER aircraft, lifting the total to 18.
Laderman added three would start service from next summer, while the fourth one would be delivered at the end of next year. (Reporting by Giulia Segreti; Editing by Sudip Kar-Gupta and Mark Potter)