Deliveries of CFM Leap engines are about to overtake those of the CFM56 for the first time, marking a watershed moment in the 44-year history of the General Electric-Safran joint venture.

Combined deliveries of the two engine families will set a record around 2,100 this year, despite production issues with Leap-1Bs for Boeing. Leap output will double to around 24 a week, with more than 1,000 of them destined for the Airbus A320neo, Boeing 737 MAX and Comac C-919 production lines; the rest will be CFM56s.

Last year, Leaps accounted for 450 of the record 1,900 engines that CFM shipped.

“The challenge is to produce the incredible number of engines that we have sold over the last years,” says CFM International president & CEO Gaël Méheust. “We have a backlog of 15,200 engines and will be delivering more than 2,000 Leaps a year by 2020.

“The ramp up is unprecedented in the history of commercial aviation. We'll have more Leap engines in service after five years than we had after 25 years of the CFM56.”

CFMI’s challenge is complicated by orders for the classic CFM56 holding stronger than had been anticipated, even as Leap sales surge. Despite the launch of the Leap family in 2008, the CFM56 has gone on to enjoy the bulk of its best sales in the years that followed amid mushrooming orders for current model A320s and 737s. Including the engines slated for delivery this year, CFM will have delivered 7,385 CFM56s since 2014 alone. This includes 2016, the peak year for the program, when 1,693 were handed over. Deliveries of all CFM56 engines totaled 32,645 as of mid-June.

The surprisingly high demand for CFM56 engines has further stressed the supply chain as production resources, particularly in castings and forgings, could not be switched as quickly as planned from one engine to the other.

Resulting delays have put Leap deliveries four to six weeks behind schedule, but Méheust is confident they will be fully caught up by the end of the year.