Do you like big-risk, roller-coaster stocks that are in a straight-down nosedive? Well, then, welcome to Monday morning's biggest percentage loser on the Nasdaq: air cargo courier and aircraft ground service specialist Air T (NASDAQ:AIRT).

Big risk
Nothing exemplifies "big risk" more than a $30 million micro cap with a majority of its sales tied to one customer, even if it is Motley Fool Stock Advisor recommendation FedEx (NYSE:FDX). When Air T reported first-quarter results Friday, 65.2% of sales came from air cargo, and 98% of the company's aircraft revenue was covered by its FedEx contract.

Headed down
The primary force driving earnings down by 47.8% this quarter compared with the year-ago period was the company's other subsidiary, Global Ground Support, which produces deicing equipment. In February, one of the company's 12 freestanding deicers collapsed in Philadelphia on an aircraft operated by US Airways (OTC BB: USABQ). It has since been determined that there were structural defects in the booms, which a subcontractor designed and manufactured. While these are the only deicers of this type that the company has installed, repairs are currently estimated to cost $373,000 (resulting in a $0.09 charge to this quarter's earnings), and the company has filed a suit against the subcontractor to recover expenses and other damages. No lawsuit, so far, has been filed against Air T in the matter.

Global was the business that saved the company's bottom line in fiscal 2005, which ended in February 2005. With only 41% of sales, Global increased its operating income by 45% to $3 million. Air cargo, meanwhile, saw profits drop 46.3% to $2.1 million.

Current problems at Global have 2006 earnings headed down right along with the stock. Isn't there a version of Murphy's Law for situations in which a single large risk exists (in this case, the FedEx contract), but other less probable risks manifest instead?

Roller-coaster stock
At $11.40 a share, the stock is still above its 52-week low of $10.03, but it's well off the 52-week high of $35.50 a share. See this chart to view the complete roller-coaster action. And expect more roller-coaster action ahead.

While the FedEx contract is renewable annually, it can be canceled with 30 days' notice. That's not good, but Air T believes that is the standard procedure in its business. If there is any upside, it's that Air T leases 95 of its 97 aircraft from FedEx (it owns the other two), and that means contract cancellation wouldn't leave the company saddled with the cost of maintaining assets that aren't producing revenue.

Increased spending in the military and Homeland Security sectors has helped Global offset weakness in commercial airline spending, and it could help moderate the company's decline by keeping revenue at a relatively steady state.

Air T has more cash than debt and can generate copious amounts of operating cash -- like the $1.7 million in the comparable quarter last year, versus $346,000 this quarter. Still, there is substantial risk in owning a micro cap that relies so heavily on one customer.

The stock is taking a dive today on what appears to be a one-time event. Curious investors should do their homework and see whether this stock has plummeted right into bargain territory.

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Fool contributor W.D. Crotty does not own shares in any of the companies mentioned. Click here to see The Motley Fool's disclosure policy.