In 1981, when Airbus SE announced it would develop a new single-aisle aircraft to compete with Boeing Co., the Boeing 737 was still dominating the market.

This American-made narrow-body aircraft had already been in service for more than a decade, reshaping the aviation industry by reducing operating costs and improving profitability on short-haul routes. By 1988, when Airbus began producing its emerging A320, Boeing had already delivered approximately 1,500 of its cigar-shaped bestseller, establishing a commanding lead.

Now, after nearly four decades of effort, Airbus has finally caught up: according to aviation consulting firm Cirium, the A320 series is poised to surpass its American competitor to become the most delivered commercial aircraft in history. Data shows that as of early August, Airbus had narrowed the gap to just 20 aircraft, with the A320 series achieving lifetime deliveries of 12,155 units. This gap will likely disappear next month.

Airbus A320 Set to Surpass 737 as Best-Selling Aircraft Cumulative deliveries since each aircraft program's launch

Max Kingsley-Jones, head of consulting at Cirium Ascend, wrote in a recent social media post about the A320: "Did anyone predict back then that it would become the sales champion and reach such high production volumes? I certainly didn't, and Airbus probably didn't either."

The A320's success reflects the European aircraft manufacturer's trajectory over decades - from industry newcomer to formidable competitor, ultimately surpassing Boeing. By the early 21st century, the A320 and its variants were already delivering more aircraft annually than the 737 series; in 2019, its total order book also exceeded that of the Boeing model. However, in terms of commercial aircraft's historical delivery volumes, the 737 had stubbornly maintained its top position.

Initially, Airbus faced an uphill battle. The European aircraft manufacturer was founded in 1970 through a consortium of aviation manufacturers with support from European governments, but it lacked a complete aircraft product line at the time. Internal disputes hindered everything from product planning to manufacturing, and leadership decisions had to carefully balance French and German commercial and political interests.

Even then, Airbus clearly recognized that to become Boeing's primary competitor, it needed to establish a foothold in the narrow-body segment. Narrow-body aircraft are the most widely used type in commercial aviation, typically connecting city pairs on short-haul routes.

In his history of Airbus, journalist Nicola Clark noted that rising fuel costs and U.S. airline deregulation in the late 1970s created an opportunity for the European manufacturer, as American airline executives urgently needed a brand-new single-aisle aircraft.

To make the A320 stand out, Airbus took some risks. It adopted a digital fly-by-wire control system, which was lighter than traditional hydraulic systems, and equipped pilots with side-stick controllers positioned at their left and right hands rather than a central control wheel. Additionally, the aircraft had higher ground clearance than the 737 and offered two engine options, providing customers with greater flexibility.

Airbus's gamble paid off. Today, the A320 and 737 account for nearly half of the world's active commercial aircraft fleet. The A320's success stands in stark contrast to strategic missteps like the A380 large aircraft - which had a short lifespan due to airlines' difficulty in achieving profitable operations. Boeing had believed that smaller, more flexible aircraft like the 787 Dreamliner would be more advantageous, a prediction that later proved correct.

However, the long-term dominance of these two narrow-body aircraft has raised questions about the vibrancy of the duopoly system - a system that tends toward stability rather than innovation. Both manufacturers have repeatedly chosen to make incremental improvements to their bestselling models to extract higher efficiency rather than spending higher costs to design replacement aircraft from scratch.

Airbus was first to equip its A320 with new engines, making the neo variant a popular hit with airlines seeking to reduce fuel expenses. Under pressure, Boeing took similar action, but its approach ultimately proved disastrous. The American manufacturer introduced the 737 MAX, installing more powerful engines on the aged, low-profile framework of this model.

An Airbus A320neo using sustainable aviation fuel.

To handle the greater thrust and maintain balance, Boeing installed an automated flight stabilization system called MCAS on the aircraft. However, regulators later found that the MCAS system was one of the causes of two fatal 737 MAX crashes, leading to a global grounding of the model for 20 months starting in 2019.

Recently, Airbus has also been troubled by issues with the fuel-efficient engines equipped on the A320neo. Defects in the high-tech coatings used to withstand high temperatures on Pratt & Whitney's geared turbofan engines have forced airlines to send aircraft for additional maintenance, creating backlogs at repair facilities and grounding hundreds of aircraft awaiting inspection and repairs.

As both narrow-body aircraft series approach the end of their evolutionary journey, analysts and investors are asking what comes next. China is attempting to break into the market with its domestically-produced COMAC C919 model, which is already operational in China but has not yet received certification to fly in Europe or the United States.

Boeing CEO Kelly Ortberg stated in July that the company is internally developing next-generation aircraft but is waiting for engine technology and other factors to mature, including restoring cash flow after years of setbacks.

"This is not something for today, and probably not for tomorrow either," he said during a July 29 conference call.

Airbus's healthier financial position gives it greater flexibility in exploring design breakthroughs. CEO Guillaume Faury had planned to launch a hydrogen-powered aircraft in the mid-2030s - possibly featuring a radical "flying wing" design - but later postponed this plan to focus on developing a conventional A320 successor.

The Toulouse, France-based company is considering open rotor engines, which save fuel through their structure rather than pushing performance improvements at the physical limits like current jet turbines.

Faury called the A320 "a fairly old platform" at the Paris Air Show in June and confirmed plans to launch its successor by the end of this decade, expected to enter service in the mid-2030s.

"I am very focused on preparing for the next-generation single-aisle aircraft," Faury said. "We are very determined and very committed to this."