How Safe Is That Plane?

The NTSB found multiple causes for the accident. One was a formula, since changed, that used inaccurate passenger weights to calculate an airplane's weight and balance before takeoff. Primarily, though, the NTSB focused on faulty maintenance procedures and inadequate oversight.

Blame was assigned to Air Midwest for lacking proper administration of its hangar, the Raytheon Aerospace inspector for failing to detect the incorrect rigging of cables and the FAA for a lack of oversight of Air Midwest's maintenance program.

"There were some big holes there," says consultant John Goglia, who served on the NTSB while it investigated the Charlotte crash. "The airline's repair station was staffed by people who didn't work for the airline. The FAA inspector sitting in Wichita watching that certificate was unable to see whether those people were trained or not trained. He might have raised the flag if he had."

Daily Business

To be sure, the North Carolina accident was one event, but it does give rise to questions about the extent to which outside workers are used, how well they're qualified and to what degree they're monitored internally and externally.

The shift is continuing unabated, and the maintenance, repair and overhaul businesses, known in the industry as MRO, is booming. Worldwide, third-party maintenance is a $41 billion business, and it's growing at nearly 5% annually, according to recent estimates.

A survey by Overhaul and Maintenance, an industry trade magazine, predicted that the MRO market for commercially operated jets will reach $52 billion by 2012. Engine work accounts for 42% of the business, the magazine says, while airframe heavy maintenance makes up 21%.

Smaller players aren't the only ones getting the contracts, either. American, Delta(DAL Quote) and United all do work for other airlines.

For instance, even though it has led the move by U.S. carriers to outsourcing, United did about $200 million worth of airframe maintenance for outside carriers in 2006. The carrier is now considering a spinoff of its maintenance division.