Stand on an airport apron when a 737 MAX taxis past, then watch an A320neo family aircraft pull up behind it. Two jets from rival manufacturers, born from decades of fierce competition, shaped by entirely different engineering philosophies. And yet, listening carefully, they share something fundamental: very nearly the same heartbeat.
The CFM LEAP engine is one of those quietly extraordinary things in aviation that enthusiasts sometimes overlook precisely because it’s everywhere. It powers the 737 MAX family and the A320neo family (as the LEAP-1B and LEAP-1A respectively), plus the COMAC C919. A single engine program at the centre of three of the most commercially significant narrowbody jets flying today. That’s a remarkable position to occupy, and the engineering behind it is worth pausing over.
CFM International is itself a fascinating entity — a 50/50 joint venture between GE Aerospace and Safran Aircraft Engines, two companies that would ordinarily be bitter rivals. The partnership has been running since the 1970s, producing the enormously successful CFM56 that powers countless previous-generation 737s and A320s. The LEAP is the CFM56’s successor, and it represents a genuine generational leap rather than an incremental refinement.
The headline technology is the use of carbon fibre composite fan blades with a woven 3D architecture. CFM calls this their proprietary 3D woven resin transfer moulding process. The blades are lighter than titanium equivalents and can be made with an aerodynamic sophistication that traditional manufacturing can’t easily achieve. The result is a wider, slower-turning fan that moves more air with less noise and better efficiency. You can see it immediately at the gate: the LEAP’s fan nacelle is noticeably larger than the CFM56’s, which is precisely why Boeing had to reposition the engine further forward and higher on the 737 MAX to maintain ground clearance.
Then there’s the combustor. The LEAP uses a TAPS (Twin Annular Pre-Swirl) combustor design, which mixes fuel and air more thoroughly before ignition. Better mixing means more complete combustion, which translates to lower fuel burn, reduced NOx emissions, and a longer-lived hot section. These aren’t marginal improvements — the LEAP delivers something in the region of fifteen percent better fuel efficiency compared to the CFM56 generation, which is significant when you’re talking about the engines that power the world’s most-flown routes.
What makes the LEAP story interesting beyond the specs is the engineering compromise embedded in the LEAP-1A versus LEAP-1B distinction. The LEAP-1A, fitted to the A320neo family, has greater design freedom because the A320 was re-engined from scratch with more available ground clearance. It can run a slightly larger fan diameter. The LEAP-1B on the 737 MAX is constrained by the legacy 737 geometry, requiring some clever packaging to fit within the airframe’s dimensional limitations. Same core family of engines, subtly different expressions of what the airframe will accept.
That duality is what makes the LEAP so fascinating to think about. It’s simultaneously a symbol of how modern aviation has standardised around shared technology, and a reminder that the physical constraints of each airframe are completely unforgiving. Physics doesn’t care about parts commonality targets.
Next time you’re at the gate and that unmistakable scalloped nacelle edge comes into view — those chevrons around the exhaust nozzle, designed to reduce jet noise by encouraging smoother mixing of the exhaust and bypass air — take a second to appreciate what you’re looking at. A piece of engineering that had to be brilliant twice, in two different ways, for two different aircraft that happen to be the backbone of global short-haul aviation. That’s not a coincidence. That’s a genuinely impressive act of applied engineering.