Boeing is accelerating introduction of all three versions of the 737 MAX by six months.

The first 737-8 is now due for first delivery towards the beginning of the third quarter of 2017, rather than in the fourth quarter. The 737-9 will follow 18 months later and that is followed by the -7 another 18 months later.

“Things are going so well,” Boeing Vice President and General Manager Airplane Development Scott Fancher said at the Paris Air Show on Wednesday. “We anticipated the opportunity to accelerate MAX from day 1.”

Boeing has gained more confidence in speeding up the MAX schedule after having met development milestones with more ease than expected.

The schedule change means the aircraft is now likely to be around two years behind the competing Airbus A320NEO. Boeing claims the 737-8 will burn 8% less fuel than the A320NEO despite the smaller fan diameter of its version of the Leap engine. “We would not put a bigger fan diameter underneath the wing even if we were not space-constrained,” Vice President 737 MAX Product Marketing Joe Ozimek said. “Bigger fans weigh more and cause more drag.”