) -- AIG shares got pummeled Tuesday because of potential woes in its aircraft leasing unit, but the same issues affect

CIT Group

(CIT) - Get Report


Royal Bank of Scotland

(RBS) - Get Report

, both of which saw their shares rise on the same day.

The problem for AIG, according to

The Wall Street Journal

and bond research firm


, is that its aircraft leasing unit needs a strong credit rating to enable it to raise money cheaply so it can buy aircraft and lend it out at higher rates.

It stands to reason that similar dynamics are at work in the case of CIT Group and RBS, two other companies that have aircraft leasing units and have seen their credit ratings slip. It's worth noting that all three companies are believed to be seeking sales of these divisions, the most recent being RBS, which reportedly hired Goldman Sachs as an adviser in the process on Sept. 9.

The value the market is placing on AIG is far from rooted in fundamentals. As is the case with


(C) - Get Report

, there are so many variables at play, from lawsuits to politics related to the government's giant equity stake, it is nearly impossible to say whether Tuesday's selloff is justified, or if it shouldn't have been three times as severe. However, if AIG is selling off in part because its aircraft leasing unit is attached to a company with a too-low credit rating, then shares of RBS and CIT could come under similar pressure.


Written by Dan Freed in New York