Late last month, Boeing (NYSE:BA) acknowledged a new problem with its troubled 737 MAX aircraft family. Boeing is currently working on a fix for this data processing issue, which is tangentially related to the initial software flaws that led to two fatal crashes over the past year.

However, the latest software update won't be ready until September. Next, Boeing will need to satisfy the FAA and a host of other regulators worldwide that the 737 MAX is finally safe to fly. Even after that, it will take at least a month for airlines to complete required maintenance and training activities so that they can return their 737 MAX fleets to service.

As a result, American Airlines (NASDAQ:AAL) and United Airlines (NASDAQ:UAL) both extended their 737 MAX flight cancellations recently. And Southwest Airlines (NYSE:LUV) is sure to follow suit before long.

The 737 MAX grounding gets worse at United Airlines

When the Boeing 737 MAX was grounded, United Airlines had just 14 in its fleet, significantly fewer than either American or Southwest. This meant that the carrier was able to keep flight cancellations to a minimum during the spring, mainly by substituting other aircraft types for the 737 MAX.

A United Airlines plane on a runway

The 737 MAX grounding is starting to have a bigger impact on United Airlines. Image source: United Airlines.

At first, United Airlines had more aggressive targets for putting the 737 MAX back into service than its rivals. Until late May, the carrier still had the 737 MAX returning to its flight schedule in early July. More recently, it had extended the cancellations into early September.

Last week, United scrubbed all 737 MAX flights through Nov. 3, giving it the latest target for putting the type back into service among the three U.S. airlines that operate it.

As the 737 MAX grounding has dragged on, the impact on United customers has worsened. The airline was supposed to grow its 737 MAX fleet from 14 as of mid-March to 30 by the end of September. Thus, United has had to cancel about 2,100 flights in September and 2,900 flights in October, compared to fewer than 1,400 in July.

American Airlines follows suit

As of last Friday, American Airlines was still saying that it had no updates to share regarding its plan to reintroduce the 737 MAX in early September. Not surprisingly, the carrier bowed to the inevitable over the weekend. American extended its flight cancellations -- approximately 115 per day -- through Nov. 2.

A rendering of a parked American Airlines plane

American Airlines has canceled all 737 MAX flights through early November. Image source: American Airlines.

With the 737 MAX grounding lasting far longer than initially expected, American Airlines also recently suspended a route for the first time during the crisis. The airline temporarily stopped flying from Dallas-Fort Worth to Oakland on July 6, due to its aircraft shortage. Customers can still fly nonstop from Dallas to the two other Bay Area airports or to Oakland via American's Phoenix hub.

Southwest Airlines, which has been relying on the 737 MAX for a much greater proportion of its daily schedule, has suspended more than a dozen routes, according to The Points Guy. This includes a mix of routes with heavy competition, low-traffic routes, and longer-haul flights that use too much aircraft time to be worthwhile right now.

Expect even more flight cancellations ahead

As of now, Southwest Airlines has only canceled its 737 MAX flights through Oct. 1, but there is virtually no chance that the aircraft will be ready to return to service by then. Even United Airlines and American Airlines may need to cancel more flights if any new problems are discovered or if the FAA waits for an international consensus to develop before recertifying the 737 MAX.

In fact, a growing number of industry officials believe the Boeing 737 MAX grounding could continue until January 2020, according to The Wall Street Journal. That would force Southwest, American, and United to cancel tens of thousands of additional flights.

Airline officials and Boeing will surely try to get the 737 MAX operational earlier than that, to meet holiday-season demand. But whether or not that proves feasible, there is likely to be at least one more round of flight cancellations for all three airlines, extending the pain from the Boeing 737 MAX grounding.

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