What happened

A potential return of the Boeing (BA 1.34%) 737 MAX to Chinese airspace failed to materialize over the weekend. Investors remain worried about when the plane will fly again in this all-important market, sending Boeing shares down as much as 3% on Monday morning.

So what

Boeing is on the rebound after a difficult two years, weighed down first by the grounding of the 737 MAX following a pair of fatal incidents and then by the pandemic, which cut demand for air travel. Airlines are once again filling their planes, and the 737 MAX has been cleared in most markets, but China remains a stubborn holdout.

There are signs a return could be near. Earlier this month, a 737 MAX operated by MIAT Mongolian Airlines was allowed to fly over Chinese skies en route to Guangzhou, China. And China Southern Airlines Co. had two 737 MAX flights on its schedule for this weekend. But those flights were cancelled prior to takeoff, denying Boeing an important milestone in its recovery.

It is hard to overstate how important China is to Boeing's long-term future. As recently as 2018, China accounted for about one-quarter of jet airplane deliveries. Overall, Boeing expects Asian markets to account for roughly 40% of long-term global demand for new airplanes.

Now what

There's no reason to believe the Boeing 737 MAX won't eventually be cleared to return to service in China, but after a series of delays and continued geopolitical tensions between the Chinese and U.S. governments, investors will sleep much better once that day finally comes and we can stop trying to read tea leaves.

Over the long term, there is a massive global need for new planes as emerging markets continue to develop and established economies try to become more fuel efficient. Boeing, thanks to its duopoly in large aircraft, is well positioned to soak up a lot of that demand.

But Boeing also took on a lot of debt, as well as hits to its reputation, during the 737 MAX debacle. The company's total long-term debt today is more than 400% where it was in 2018. The only way for Boeing to normalize its balance sheet is cash flow, which means an uptick in deliveries.

Until there is business as usual in China, it's hard to get too excited about Boeing's near-term outlook.