Boeing’s redesigns keep iconic low-profile 737 flying amid evolving aviation needs

The latest generation, the Boeing 737 MAX series (including MAX 8 and MAX 9), uses CFM LEAP-1B engines that also have a diameter of 69 inches. For these models, Boeing further modified engine placement by moving them forward and higher on the wing to preserve necessary clearance beneath the aircraft.

In comparison to competitors like Airbus’s A320neo family—which features even larger LEAP-1A engines but sits higher off the ground—the unique challenge for Boeing has been adapting its long-standing design to modern requirements without significantly altering the aircraft’s profile or operational characteristics.

There are benefits to having an aircraft close to the ground. "Primarily, the 737's proximity to the ground makes for easier ground handling, as in-built stairs can be used for passengers to board and disembark, rather than relying on facilities at the airport such as aircraft steps or jetbridges," according to industry analysis. This contributes to faster turnaround times and lower costs for airlines.

However, this design also presents drawbacks: "Firstly, with the engines being so close to the ground, there is a greater risk of them ingesting FOD (foreign object debris) from the airfield... Secondly, ...there can be an increased risk of tailstrike incidents on take-off."

Southwest Airlines is currently recognized as having the largest fleet of Boeing 737s worldwide. The airline operates only this model type—a strategy that helps reduce maintenance expenses and streamline pilot training processes [https://www.ch-aviation.com/portal/news/132434-southwest-airlines-to-phase-out-all-b737-classics-by-end-2017]. United Airlines is another major operator with over five hundred units across six different variants.

Despite its commercial success over decades, recent years have brought significant challenges for Boeing’s flagship narrowbody jet. Two fatal crashes involving Lion Air Flight 610 in October 2018 and Ethiopian Airlines Flight 302 in March 2019 led global regulators—including the US Federal Aviation Administration—to temporarily ground all Boeing 737 MAX planes [https://www.faa.gov/newsroom/faa-statement-grounding-boeing-737-max-aircraft]. Operations resumed nearly two years later after safety reviews were completed. In January 2024, another incident involving an Alaska Airlines MAX model brought renewed scrutiny.

The evolution of engine size and placement demonstrates how Boeing has had to adapt its best-selling product over time while balancing operational efficiency against changing technological demands within aviation.