The 55-year old seaplane used to market the Red Bull energy drink at major sporting events and air shows was decommissioned and disposed of by the Coast Guard in 1976 because they considered it no longer safe to fly given the age of its wings.
But it flies over the heads of hundreds of thousands of people a year under an "experimental airworthiness certificate" granted by the FAA in 2008.
In a written response to questions, a Red Bull spokesperson, Patrice Radden, said: "Neither Red Bull nor any of its pilots or flight crews have or would operate an aircraft that is known to be unsafe or in an unsafe manner."
The aircraft is a Grumman-built HU-16E "Flying Albatross."
New Orleans Saints football star Reggie Bush, a Red Bull paid spokesperson, was filmed flying the plane in the left pilot's seat, climbing into the plexi-glass nose of the aircraft and sticking his head out of an open window.
"I stuck my head out the window which never in a million years I thought I would be able to do," Bush says on a Red Bull promotional video posted on the company's website.
Earlier this month, the Red Bull plane flew over thousands of college students on spring break at Lake Havasu, Arizona.
A spokesman for the FAA said the agency was "comfortable" with the use of the airplane, even if it is flying over the heads of thousands of people a year.
Red Bull says the plane is operated in full compliance with FAA regulations.
"It's terribly unsafe because the wing could fall off at any time," said Bill McNease, a former FAA safety inspector who helped initiate an earlier investigation of the plane when he was with the FAA in 2006.
"The long wing versions of this airplane have a definite, if you want to call it, drop dead time. When they reach a certain amount of flight hours, that's it," said McNease in an interview with ABC News Chief Investigative Correspondent Brian Ross for Good Morning America.
The FAA investigation of the Red Bull plane followed the 2005 crash of a similar seaplane, operated by Chalks Ocean Airways in Miami.
Twenty people were killed when the plane's right wing separated on take-off.
"There's the possibility that the same thing could happen" with the Red Bull plane, said McNease.
The FAA investigation relied on a confidential U.S. Coast guard report, obtained by ABC News.
The Coast Guard said it had stopped using the plane in 1976 because "all available service life appears to have been expended."
As of 1971, Coast Guard records show, the plane had logged 8,068 flight hours.
Yet in an application for an FAA airworthiness certificate 37 years later, in 2008, the owners of the plane who lease it to Red Bull claimed the plane had only 7,100 hours.
Somehow, the total flight time had been rolled back 968 hours, tantamount to rolling back the odometer on a used car.
"You can't roll back hours," said former FAA inspector McNease.
The Red Bull spokesperson said the plane's owners relied on data it received when it bought the plane in 2000.