New York (CNN Business) Boeing has bested Airbus as the world's largest aircraft maker for most of this decade. That's about to change in dramatic fashion.

Airbus has already delivered 150 more jets thanthrough the first six months of the year: Airbus is winning 389 to 239, according to sales figures reported this week.

Airbus' commanding lead is especially significant because the race between the two companies has historically been tight. Last year, for example, Boeing delivered 806 aircraft last year to Airbus' 800. 2015 was the only year this decade in which one of the two airplane manufacturers delivered 100 more planes than the other.

The gap between them is almost certainly going to get wider. Boeing has not been able to deliver any of its bestselling 737 Max planes since March, when those jets were grounded . That month, one of the jets crashed in Ethiopia and killed all 157 people on board. It was the second fatal crash of a 737 Max in less than six months. In total, 346 people died aboard the two planes. Boeing probably won't get approval to fly the 737 Max again until the end of 2019 at the earliest — much later than what was initially expected.

Boeing and Airbus dominate the commercial aircraft market , and both companies have a backlog of thousands of jets that will keep them busy making planes for years to come. That has kept new orders modest for both companies, even before the 737 Max grounding.

Investors view deliveries as a more important metric of success than orders. Airlines don't pay most of the price of a new jet until it is delivered, meaning that the aircraft makers' revenue, profits and cash flow depend upon deliveries.

The good news for both companies is that the demand for air travel, and new fuel-efficient planes, is growing. That means both are building and delivering planes at a much faster pace than in the past. In 2011, the last time that Boeing was behind Airbus in plane deliveries, Boeing's deliveries stood at 477, Airbus at 536.

"It doesn't really matter if one delivers 10 more planes than the other. The point is the numbers for both are big," said Cai von Rumohr, aerospace analyst with Cowen.

Boeing has continued to build the 737 Max, though at a reduced rate. Boeing will probably have about 400 of the jets completed but undelivered by the end of the year. The huge supply of completed 737 Max jets at the end of this year likely will allow Boeing to move back into the lead in deliveries in 2020.

The key will be how the two aircraft makers perform in 2021 and beyond. Airbus is well positioned to move back into the lead at that point because of its lead with single aisle jets, said von Rumohr.

The key question will be how soon Boeing can get its 737 Max lineup to full speed once the Max returns to service.