The rapid growth and evolution of the MRO industry has piqued the interest of potential investors, who must weigh whether this integral part of air transportation is worth the risk. On one hand, investors are concerned about the grounding of hundreds of older passenger and cargo aircraft, and they are questioning the adequacy of outsourcing regulatory oversight. On the other hand, the continued growth in the outsourcing of major maintenance bolsters the segment's money-making potential.

The financial community seems split on what to do. With the U.S. and other economies teetering above the abyss, some say the timing couldn't be worse. They recommend a wait-and-see posture on investing in MROs. Others say now is the perfect time to invest in this industry, a time when they can get more for their money.

Another consideration for investors is the type of MRO company in which to invest. At present, there are independent MRO providers, some aligned with original equipment manufacturers (OEMs) and others that are not. There are engineering service providers, PMA manufacturers, parts distributors, and in-house airline operations that are for sale at the right price.

Until the credit crunch on Wall Street, and subsequent failures of several lending institutions, there was a lot of investment activity in MRO.

In August, General Dynamics, parent of business jet maker Gulfstream Aerospace, announced its intension to buy Switzerland-based Jet Aviation for $2.25 billion. Considered by some to be the premier MRO for business aircraft, Jet Aviation has 25 facilities in the Americas, the Middle East, Asia and Europe. This global reach is one of the primary reasons General Dynamics is purchasing Jet Aviation. General Dynamics hopes to close the deal by the end of the year.

"There has been a frenzy of MRO activity in the last 18 months," said Tim Hoyland, a partner with Oliver Wyman, a Dallas-based consultancy.

"In the spring, we were seeing a fair amount of interest in the private equity market for MROs," added Chris Doan, president and CEO of Denver-based TeamSAI Consulting.

Earler, PEMCO World Air Services was sold to Sun Capital Partners, a private investment firm specializing in leveraged buyouts. Goodrich sold its heavy maintenance division, Goodrich Aircraft Technical Services, to Sydney, Australia-based Macquarie Group, formerly Macquarie Bank, a global investment banking and financial services group. The Carlyle Group sold engine MRO Standard Aero and Landmark Aviation, a group of FBOs, to the Dubai Aerospace Enterprise (DAE) for $1.9 billion. DAE has since re-sold Landmark's FBOs to Chicago equity firm, JTCR Golden Rauner and Encore.

"Investors are paying a very high multiple for assets like StandardAero, which was sold at 14 times enterprise value to EBITDA (earnings before interest, taxes, depreciation and amortization)," said Richard Stoneman, an analyst with Dundee Securities in Toronto.