Boeing 737 sales soared high in the penultimate week of 2015. Image source: Boeing.

With firm orders for 1,007 planes on its books already, Airbus (OTC:EADSY) looks like a lock to win the crown as the best-selling plane maker of 2015. But Boeing (NYSE:BA) isn't giving up without a fight.

In its final weekly Thursday order report of the year, Boeing showed evidence of a massive push to close out the year strongly, adding 166 new orders to its books, and rushing to overtake its rival. According to the report, during the past week alone, Boeing sold 166 new planes -- nearly 30% as many as it sold during the preceding 50 weeks combined. Here's how the new orders break down:

  • Three new single-aisle 737s sold to Jet (a deal first reported last week).
  • 20 more 737s ordered by Delta Air Lines (NYSE:DAL). This may seem curious given Delta's high-profile Twittering tiff with Boeing over the price of the latter's 777 airliners last week. But disputes aside, Delta needs to buy planes somewhere -- and Boeing builds some of the best.
  • A whopping 143 more 737s ordered by "Unidentified Customer(s)."

And now, here's how the rash of new orders upped the company's order count for the year to date:

  • 633 gross orders for single-aisle 737s
  • 97 Dreamliner 787s
  • 58 widebody 777s
  • 49 Boeing 767s
  • six 747s

That works out to 843 gross orders for Boeing planes. No new cancellations were reported for the week, so the cancellations number is still set at 100. That makes net orders received through all but the final week of the year 743 planes. Or in other words -- still 264 fewer planes than Airbus has sold.

Bad news, worse news?
Although there's still a week left on the calendar, this is the last report on plane orders that Boeing plans to publish in 2015. The year's final tally, including sales from last Wednesday through New Year's Eve, will be published in Boeing's "final 2015 orders" report on Jan. 7, 2016.

Thus, we won't know with 100% certainty which company will win this horse race for another two weeks. Still, with Airbus having sold roughly four new planes for every three Boeing sold through today's date, only one more week to go before the calendar flips over, and Airbus still to report its orders for all of December, the chances for Boeing overtaking Airbus this year seem slim. Odds are, when all's said and done and both plane makers have reported their final sales tallies in January, we'll learn that Airbus has once again beaten Boeing in plane sales -- for the third year in a row.

As we explained last week, that's probably not good news for Boeing -- albeit, the last-minute sales rush last week may reverse the course of Boeing's declining backlog. What worries me more, though, is that, in rushing to win orders at the last minute, and attempting to overtake Airbus -- a quest probably doomed from the start at this point -- Boeing may have granted too generous pricing terms to customers willing to help it out by placing their orders in December 2015, rather than, say, January 2016. Put bluntly, Boeing may have sacrificed profit margins in an attempt to win sales.

What it means to investors
If that's true, it will continue a trend in declining gross margins at Boeing that, according to data from S&P Capital IQ, now stretches six years in length. From a recent high of 19.4% gross margins in 2010, Boeing's gross has slipped as far as 15.3% during the past 12 months.

Will it prove true? Only time will tell. Make a note on your calendars to check back here when Boeing next reports earnings, when we'll be sure to examine the issue. Boeing reports Q4 and full-year 2015 results on Jan. 27, 2016.