Either the Federal Aviation Administration is on the warpath, or our nation's carriers desperately need to refresh their fleets.

Earlier today, American Airlines parent AMR (NYSE: AMR) grounded 200 flights after regulators, following a maintenance audit, raised questions about the wiring in its fleet of MD-80 aircraft. It's the second time in a week that American has canceled flights because of maintenance issues.

The MD-80 is a medium-range aircraft based on the original McDonnell-Douglas DC-9, which was first introduced in 1965. Boeing (NYSE: BA), which acquired McDonnell-Douglas in 1997, no longer manufactures new models of the MD-80.

Don't overlook that last point; it's crucial. Why? The FAA is very likely citing old jets. Not long ago, Southwest's (NYSE: LUV) aging fleet of 737 aircraft caught regulators' eye.

Who's next? Delta (NYSE: DAL)? Alitalia? SAS? All three fly the MD-80.

We don't know, of course. We do know that, because Southwest flies the 737 and faces its own set of maintenance concerns, these issues aren't exclusive to aircraft. And that means any carrier -- Northwest (NYSE: NWA), JetBlue (Nasdaq: JBLU), UAL (Nasdaq: UAUA) -- could be next.

So, let's not pick on American too much. If the pattern holds -- and, in investing, it usually does -- there's plenty of finger-pointing still to come.

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