"American Airlines Shares Fall 33%." So blared the headline on page B1 of today's Wall Street Journal. So if it was a black day for AMR (NYSE: AMR) shareholders, at least they have the comfort of knowing they're "famous."

Today, these same shares are bounced back 20%, so clearly AMR shareholders have their hands full trying to figure the odds of a bankruptcy filing (AMR says it's bunk, by the way). I won't impose on them further with today's column. Instead, today I want to take a step back and consider what implications AMR's rumored imminent bankruptcy filing has for everyone else in the market -- beginning with Boeing (NYSE: BA).

Losers ...
As you may recall, Boeing and AMR shared headlines back in July, when, to win part of AMR's business, Boeing agreed to a wholesale rethink of its strategy for the 737 airliner. AMR was in the market for a few hundred airplanes, you see. But it was leaning heavily toward super-fuel efficient A320 "neos" from Airbus. Boeing, not pleased with this prospect, shelved plans for a major overhaul of its venerable 737. Instead, it offered AMR a version dubbed the 737 MAX, equipped with new LEAP engines from General Electric (NYSE: GE) / Safran. The move helped Boeing win part of AMR's business.

I use the word "win" loosely, however, because it turns out this was not much of a victory. Winning AMR's business also required Boeing to cover the airline's costs through a lease financing arrangement. Boeing also seems to have given steep discounts from the list price of its jets -- by my calculations, on the order of 35% off. And if AMR now goes into bankruptcy, as some pundits are projecting, Boeing may not even get all the sales it bargained for. It may have changed its 737 strategy for nothing.

... and winners
That's not to say that no one benefits from AMR's troubles, however. Short-sellers, for example, are enjoying a field day. Also benefitting will be AMR's rivals, from giants Delta (NYSE: DAL), US Airways (NYSE: LCC), and United Continental (NYSE: UAL), to discount liners like jetBlue (Nasdaq: JBLU) -- each of which faces a weakened rival in AMR. Each of these may enjoy an influx of customers as American Airlines loyalists worry that their frequent flyer miles may not be honored after an AMR restructuring, and choose to fly friendlier skies instead.

In other words, if you sold any of AMR's rivals in yesterday's panic, you made exactly the wrong call.

This article represents the opinion of the writer, who may disagree with the “official” recommendation position of a Motley Fool premium advisory service. We’re motley! Questioning an investing thesis -- even one of our own -- helps us all think critically about investing and make decisions that help us become smarter, happier, and richer.