Outsourcing by aircraft manufacturers has resulted in substandard parts being built into commercial airplanes that carry thousands of passengers daily, according to a government report.

Major manufacturers such as Boeing Co., General Electric Aircraft Engines and Bombardier/Learjet often cut costs by allowing foreign suppliers to make airplane components, but do not adequately supervise the quality of their subcontractors' work, said the report this week from the U.S. Department of Transportation's inspector general.

"This is a critical safety issue, as demonstrated by four engine failures that occurred in [fiscal] 2003 due to faulty speed sensors on fuel pumps obtained from a supplier," the inspector general's report said. "Three of the engine failures occurred on the ground and one occurred in flight. The part failures were traced to unapproved design changes made by a sub-tier supplier."

The inspector general's audit found "widespread deficiencies at supplier facilities used by major aviation manufacturers" at 20 of the 21 plants inspected.

Other major manufacturers mentioned in the report are Rolls-Royce PLC, which manufacturers aircraft engines; Pratt & Whitney, another engine maker; and Airbus Industries, which competes with Boeing to manufacture airplanes.Their subcontractors' plants the inspector general audited are located in 15 countries, including Chile, Tunisia, United Arab Emirates and Uzbekistan. Aircraft parts typically manufactured in foreign countries include passenger doors, rudders, wing flaps and wing boxes.

Common safety problems among the subcontractors were a lack of work documentation, deficient tooling calibration and inadequate employee training.