Federal taxpayers got saddled with millions of dollars in additional costs because the Defense Department accepted aircraft from Lockheed Martin in Marietta with defective engines and other "non-conforming" parts and planes that were improperly serviced, a watchdog agency is reporting.

The Marietta plant has a contract to replace engines and make other upgrades in the Air Force's aging C-5 Galaxy airplanes, in operation since 1970.

But a report by the inspector general's office for the Defense Department said Lockheed used an increasing number of non-conforming parts and services. That can include substandard parts or other parts and services that don't meet government specifications.

Among the problems discovered  after the planes were accepted were five aircraft whose engines had known design defects and aircraft whose wiring systems did not match diagrams the company provided.

How did problem aircraft slip by? The report pins blame on the government for giving the company authority to classify defects as minor, major or critical and assess whether the aircraft non-conformances should be accepted, used "as is" or repaired.

The Defense Contract Management Agency is responsible for verifying that aircraft conform to contract specifications. But the inspector general reports that the agency failed to require Lockheed to take more stringent corrective action when evidence showed that the corrections it made were ineffective. Among cases it cited, DCMA didn't step up the level of corrective actions required when an improperly fastened panel fell off an aircraft in flight; when an aircraft's fuel tanks were overfilled; and when the government couldn't verify that Lockheed was providing accurate invoices.

A tipster reported the concerns via a hotline to the inspector general's office.

Here's a summary of the findings. A link to the full report is here.

For those interested in a deeper dive on the history of the program to save the Galaxy, this has great details.