This article originally appeared as part of ongoing coverage in our premium Motley Fool Stock Advisor service...we hope you enjoy this complimentary peek!

What's happening: Shares of Air Methods (NASDAQ:AIRM), a provider of air medical emergency transportation services within the U.S., were grounded today and fell as much as 21% after the company provided an update on its third-quarter earnings expectations after the closing bell last night.

Why it's happening: According to Air Methods' third-quarter update, preliminary revenue per community-based transport fell ever-so-slightly to $11,972 compared to $11,988 in the year-ago period. Air Methods blamed the modest dip on a decrease in privately insured patients as a percentage of transports to 32.6% from 34.2% in the year-ago period.

In addition, though community-based patient transports increased by 7% to 15,789 from the prior-year period, patients transported for community bases in operation greater than one year declined by 3%, or an estimated 375 transports (consider this figure the equivalent of a retailer reporting same-store sales). As such, Air Methods now expects to report EPS in the range of $0.83 to $0.87 for the quarter compared to the CapitalIQ consensus EPS estimate of $1.07.

As Air Methods CEO Aaron Todd noted, "Quarterly fluctuations in flight volumes and net reimbursement per transport are not unusual for Air Methods; having both of these factors reflecting weakness in a third quarter is less typical. Air Methods has instituted a supplemental price increase of 3% effective October 1st to help offset these variables moving forward."