Boeing's crises have overshadowed a deeper, longer-term risk to the company's commercial passenger business. According to Agency Partners and other analysts, Boeing's share of the single-aisle airliner market, where it competes with Airbus in a global duopoly, has fallen from about 50 percent a decade ago to about 35 percent after the 737MAX's long layoff.

Airbus' single-aisle A321neo has raked in billions of dollars in orders in a recently booming market segment where the larger MAX variants are struggling to gain traction.

Without a new aircraft dedicated to this segment, analysts warn that America risks ceding a huge chunk of this market - valued by aircraft manufacturers at some $3.5 trillion over 20 years - to Europe.

But Boeing is not yet ready to agree on a plan to develop a new plane to counter the A321neo, and the two main options - move forward now or wait until later - carry financial and strategic risks, several people briefed on the discussions said.

"I'm confident that in the longer term we will achieve our goal and I'm confident in the product line," Calhoun said in April as Boeing booked new MAX orders. Asked about the company's discussions and options for a potential new plane, a Boeing spokesman said there was no immediate comment beyond Calhoun's remarks to investors.

Two options

A weakened Boeing has little margin for error, especially when it tackles the industrial problems that hamper other airliners. Boeing's first option is to strike relatively quickly, bringing to market by 2029 a 5,000-mile single-aisle airplane with 10% greater fuel efficiency. Orders could go out in 2023.

"There's no better way to burnish its image than to invest now in the future, plain and simple," says Richard Aboulafia, an analyst at Teal Group.

A new single-aisle aircraft would replace the 757, which is no longer in production, and fill a gap between the MAX and 787, confirming a reversal of earlier plans for the mid-market. The idea took a back seat at the start of the pandemic, before regaining momentum. It would also provide an anchor for an eventual outright replacement of the 737 family.

Another option is to wait for the next leap forward in engine technology, which is not expected until the early 2030s. This could be open-rotor engines with visible blades using a mix of traditional turbines and electric propulsion.

Anxious not to let near-term product decisions determine its strategy, Boeing is also prioritizing a more in-depth analysis of the investments or business changes needed to regain the top spot, analysts say.

What timing?

Both approaches carry risks. If it moves too quickly, Boeing may face a relatively simple counterattack. According to European sources, Airbus' preference is to do nothing and reserve a favorable status quo. But the European has a souped-up A321 in the works, in case it needs to counterattack an American offensive.

Such an upgrade could cost Airbus some $2-3 billion, but far less than the $15 billion Boeing would spend on a new plane. And that's not counting the hazards inherent in developing a brand new aircraft.

On the other hand, if it moves too slowly, investors may have to endure a decade of dangerously low market share in the single-aisle category, the industry's profit driver. Proponents of restraint, including soon-to-be-departed CFO Greg Smith, have a simple argument, insiders say.

Boeing has racked up a mountain of debt and burned $20 billion in cash as it has moved from crisis to crisis. "It's a different world," says one insider. "How can you think of a new plane?"

Still, some engineers at Boeing's commercial headquarters in Seattle are crying out for bold action to reassert its engineering dominance after the worst period in its 105-year history. "This should be a priority for Boeing right now," said Tom McCarty, a former senior Boeing avionics engineer. "Clearly getting back to the forefront of technological advancement."

Engine Discussions

As it ponders whether to move forward, Boeing has requested initial technical data from engine makers Rolls-Royce, Pratt & Whitney and CFM International, the joint venture of General Electric and Safran, industry sources said.

China, where state-owned COMAC is still working on the single-aisle C919, which wants to chase the B737 and A320 families, is watching Boeing's decision from the sidelines.

With a net cash position of $7 billion, an established position and assets up its sleeve, analysts believe Airbus looks the most comfortable, although it also faces its share of industry problems.

The growing pressure on the environment, reflected in the priorities of each aircraft manufacturer, is a key factor in the deliberations.

Airbus is committed to launching the first small commercial hydrogen aircraft in 2035. Its zero-emissions programme reflects its CEO's belief that disruptive technologies will play a role in the next generation of jets. But industry sources say it's no coincidence that this rhetoric is deterring Boeing from launching an interim aircraft.

Boeing has emphasized the early benefits of sustainable jet fuel (SAF). According to people familiar with the project, any new 757 aircraft would be capable of running on 100% SAF.

While Boeing supported the fuel for technical reasons, it left itself enough leeway to argue that a relatively early new aircraft would still meet the industry's environmental objectives.

Airbus, meanwhile, kept up the pressure by proposing last week to nearly double single-aisle production in four years.

While some suppliers questioned how quickly the plan was achievable, one industry executive noted that it sent a "message that Airbus is coming out of the crisis as number one and intends to stay that way".

When asked if he thought Airbus' expansion plans might prompt Boeing to launch a new plane, Airbus CEO Guillaume Faury downplayed the prospect of a new industry arms race.

"If they have confidence in the MAX and the pent-up demand they see for single-aisle aircraft, I don't see why they would be in a hurry to replace the MAX. If they are in a different situation, they might come to different conclusions," Faury told Reuters.