SYDNEY (Reuters) - Boeing Co BA.N could begin delivering the 737 MAX 10X aircraft in 2020 if airlines start ordering the largest version of its 737 MAX family this year, a senior executive of the aeroplane manufacturer said on Thursday.

The Boeing Company logo is projected on a wall at the "What's Next?" conference in Chicago, Illinois, U.S., October 4, 2016. REUTERS/Jim Young

The comments from Boeing 737 MAX chief project engineer and deputy program manager Michael Teal came as the smaller 737 MAX 9 completed its first airport taxi test in Seattle on Wednesday. That aircraft will make its first test flight in Seattle on Thursday, weather permitting, he said.

Boeing began marketing the 737 MAX 10X as an option to customers this year but has yet to receive any orders for the fuel-efficient single-aisle jetliner, which competes against the popular Airbus SE AIR.PA A321neo.

Teal said the design of the 737 MAX 10X would be firmed up by the end of this year and customers could receive the aircraft in 2020 depending on orders.

“We’ll determine (the delivery date) when we launch that program when the customers show the interest and they buy the airplane,” he said on a conference call with reporters. “Sales teams are out meeting with customers today.”

He did not specify at what date deliveries by 2020 would become unlikely if orders were not received.

Boeing in March said it had approached India's SpiceJet Ltd SPJT.BO and Jet Airways Ltd JET.NS as it gauged interest in the aircraft.

However, the heads of two major aircraft leasing companies have said the MAX 10X holds no particular attraction for their customers and would eat into rentals of other MAX models.

The 737 MAX 10X has a body 66 inches (167 centimeters) longer than the second-largest family member, the 737 MAX 9, and adds 12 seats. It will require longer landing gear as a result.

Teal said the landing gear were still in the development stage, with several concepts in prototype testing.

“We won’t hit the firm configuration on the gear and really the complete airplane until the end of this year,” he said. “All of the development tests are proving positive and we are well on our way to firming up that configuration and moving forward into production.”

The first 737 MAX 9 customer delivery is expected next year, while the first 737 MAX 8 should be delivered next month, Teal said.