WASHINGTON -- As the start of the summer travel season inches closer, the recent memory of grounded planes and missed inspections may have some of us thinking twice about flying. Now, a federal watchdog group says the Federal Aviation Administration may be asleep at the wheel not only when it comes to inspecting planes, but its parts as well.

The U.S. Transportation Department's Inspector General recently took an in-depth look at companies that supply aircraft components to manufacturers like Boeing and Learjet. The investigation found that substandard parts have entered the aviation supply chain due to poor oversight by the FAA and by the companies who buy the parts. According to the report, neither perform enough inspections-- something the inspector general found troubling since more plane components are being made overseas.

The report also cited four incidents of engine failure-- three on the ground, one in flight-- caused by a defective sensor on the fuel pumps. Full report here.

We contacted more than a dozen airline safety inspectors who told us they didn't have confidence that the FAA can continue to be an effective aviation watchdog. One former inspector general explained that the FAA simply doesn't have enough inspectors, and it's only a matter of time before a catastrophic safety lapse occurs.

"Safety is like a rubber band," said former Inspector General Mary Schiavo. "You can stretch it and stretch it, but it eventually snaps."

The FAA denies allegations that safety is slipping, and so far, no airline accidents have been attributed to faulty plane parts. The agency sent us a statement that said, "our safety record demonstrates that manufacturers are building quality, safe products but we are always open to doing our safety oversight smarter."

The FAA, however, agreed with most of the safety recommendations made by the Inspector General and said its already taken action to beef up oversight.

The National Transportation Safety Board questions whether action will be taken quickly. The agency charged with investigating plane crashes has made 400 safety recommendations to the FAA that have yet to be addressed.

"We'd certainly like to see action taken before there's a loss of life," said NTSB Board Member Debbie Hersman.