Last week, Hainan Airlines -- China's fourth-largest airline -- announced plans to order 30 more 787 Dreamliners from Boeing (BA 2.60%). The deal hasn't been officially announced yet, but the airline's plans seem to be pretty firm.

This is a significant order: $7.7 billion at list prices. (Airlines typically get discounts of about 50% off the list price, though.) But beyond the sheer size of the order, this deal is impressive because of how Boeing appears to be freeing up delivery slots for the highly sought-after Dreamliner.

Dreamliner sales have been slowing
By the end of 2008 -- still a year before the Dreamliner's first flight -- Boeing had sold more than 900 787s. However, because of the Great Recession and repeated delays in the development process, order cancellations outpaced new orders for the 787 during the 2009-2012 period.

Boeing didn't sell many Dreamliners last year. Source: The Boeing Company.

The 787 did snag more than 180 orders in 2013, largely because of the launch of the stretched 787-10, which will be the largest member of the Dreamliner family. However, net orders receded to just 41 last year, and Boeing had only bagged 4 net orders in 2015 as of March 24.

Some investors are unsettled about the slowing pace of Dreamliner orders. These worries have increased as oil prices have fallen; some analysts fear that airlines will not be as interested in upgrading to the fuel-efficient Dreamliner when they aren't spending as much on fuel.

However, one big impediment to sales has been the massive Dreamliner order backlog. Boeing has more than 800 unfilled orders for the 787: equal to nearly seven years of production at the current build rate. Even with planned production rate increases, Boeing is more or less sold out through 2020. Airlines that want small widebodies sooner have had better luck with Airbus.

Freeing up delivery slots
To win the Hainan Airlines order, Boeing has to find planes available before 2020. It may do so by convincing United Continental (UAL -2.46%) to give up some of its Dreamliner orders, according to The Wall Street Journal.

Over the past few months, United Airlines has expressed interest in trading some of its Dreamliner orders for larger Boeing 777-300ERs. The 777s are big enough to replace some of United's aging, costly-to-operate 747s: the carrier operates nine that are around the end of their 25-year useful lives. Price appears to be the main sticking point.

A win for everyone
If Boeing can hammer out final agreements with United and Hainan Airlines, everyone will win. For United Airlines, switching some 787 orders for 777s makes sense because its biggest fleet need right now is a 747 replacement, and the 777-300ER is the best option among planes currently in production.

Boeing is looking to fill the 777 production gap before the new 777X enters service in 2020. Source: The Boeing Company.

For Hainan Airlines, securing Dreamliner delivery slots within the next few years will allow the carrier to continue its growth on "long-and-thin" routes from China to the U.S. For many of these routes, the 787 is the only aircraft with the right range and size characteristics.

Boeing would probably be the biggest winner, though. Whereas it has more than 800 unfilled Dreamliner orders, it has only 272 unfilled orders for the current-generation 777. It needs to sell 40-60 current-generation 777s in each of the next few years to bridge the gap until 777X production begins, near the end of the decade.

Thus, it's in Boeing's interest to use the high demand for Dreamliners to help sell the remaining 777s. In this case, United Continental ordered its Dreamliners many years ago, which means it probably received favorable pricing compared to what's available today.

By remarketing those planes to Hainan Airlines, Boeing can probably get much higher prices. Boeing can use the additional profit from the Dreamliners to "subsidize" the sale of 777-300ERs to United Continental.

A smart move
Boeing's negotiations with United Continental and Hainan Airlines show that it is thinking about its business from a holistic standpoint. Even if Boeing were to sell United Continental the 777s at break-even, the jet maker would come out ahead thanks to the additional profit it will make from selling 787s to Hainan Airlines rather than United.

The long backlog for the Dreamliner has made it harder for Boeing to generate new orders. But by using the pent-up demand for the Dreamliner to help sell the less-popular 777, Boeing is turning a potential stumbling block into a valuable asset.