As Boeing's (NYSE: BA) protracted labor strike entered its fourth week, the airplane manufacturer got some more bad news: Airplane deliveries have fallen for a fourth straight month. As local daily The Seattle Times reported on Tuesday, Boeing delivered 44 commercial airplanes to its customers in June, 43 planes in July, and just 40 in August. Tuesday's tally for September -- 33 planes -- marks the fourth straight down month for the airplane builder.

Boeing's bad news

This news isn't entirely unexpected. Negotiations with the International Association of Machinists that broke down last month resulted in 33,000 machinists walking off the job on Sept. 13. Meaning, for more than half the month of September, Boeing wasn't building any new 737s, 767s, or 777s in Washington. (Boeing 787s are built at a non-union plant in South Carolina).

Plus, Boeing had already been slowing production of its 737s (the company's best-selling airplane) to focus on quality, hoping to avoid the repeat of an incident when a door plug blew off of a 737 midair back in January.

Still, the numbers are disturbing.

Earlier this week, Boeing updated its orders and deliveries data to reflect airplane orders and deliveries received through the end of September. Year to date, Boeing has delivered 291 commercial airplanes to its airline customers. Boeing did book 315 gross new orders, including 65 orders in September, which should have been enough to replenish its backlog (currently at 6,197 planes).

However, cancellations, conversions, and changes to the order tally to account for planes that have been ordered -- but customers might not actually end up buying -- reduced net new orders year to date to just 121 planes.

Result: Boeing's backlog is still shrinking.

How does Boeing compare to Airbus?

To fully appreciate how bad these numbers are, it's important to put them in context. Globally, Boeing's biggest competitor in selling commercial airplanes to airline customers is Airbus (OTC: EADSY). In September, Airbus reported 50 planes delivered -- so 52% better than Boeing. Airbus also raked in 235 gross new orders. That's 261% more new orders than Boeing.

So clearly, the strike (which hurts manufacturing and deliveries, but shouldn't greatly affect plane orders) isn't Boeing's only problem. And year to date, Airbus has delivered 497 airplanes to its customers, or 71% more than Boeing.

Long story short, Airbus is beating Boeing soundly in the growth rate race.

The bigger picture for investors

Investors also need to view all of the above within the wider context of how these two companies are growing -- or failing to grow -- over time. And here, the story turns to a tale of slowing airplane demand more generally.