Ultimately, Shanahan was cleared of any wrongdoing because the researchers found that his "comments on the F-35 program were essential in connection with the program's work and were in line with the comments of the F-35 program made by other senior government officials ".
But his disturbing assessment of the status of the F-35 program, in particular his concern over the lack of spare parts for aircraft, was reinforced by a separate report released Thursday by the federal oversight group.
"Flight planes F-35 could not fly nearly 30 percent of the May-November 2018 period due to a lack of spare parts," GAO said, noting that the defense ministry has "repair a backlog of around 4,300 F-35 parts."
The two reports released Thursday raised additional questions about the state of the world's most expensive weapon system. In particular, the Inspector General's report clearly shows that the inspectors considered the fact that Shanahan told them that he did not criticize the plane itself, but the program as a whole, when assessing whether it violated ethical agreements.
"Mr. Shanahan told us that he did not say that the F-35 plane was" f —- d up. "He told us that the F-35 plane was" great, "the report said. . Shanahan told us that he said the F-35 program was "f —- d up". "
"He added that these comments were" always in terms of the level of performance and the number of categories where you have … fundamental problems, "he adds, stressing that Shanghai's overall criticism of the F-35 program is based on various issues, including and "insufficient spare parts in the census" and the price per hour per hour does not decrease rapidly. "
The F-35 Combat Aircraft is considered to be the future of military aviation; deadly and diversified jet that combines sidestar abilities, supersonic speed, extreme agility, and state-of-the-art sensor technology for fusion, according to Lockheed Martin.
The aircraft, which maintains hidden capabilities, making it harder to detect enemy radars, is the favorite of President Donald Trump, who has repeatedly praised the F-35 for "invisibility".
However, the plane has also received severe criticism in recent years, after facing a long list of failures – including software problems, engines, and weapons systems.
And critics continued to express skepticism about the combat capability despite the concerns of US military leaders who say they are working out.
Several questions have been raised for the F-35 this month after one of the Japanese self-defense forces crashed into the Pacific. Since then, Japan has consolidated its remaining fleet of 12 sterile jets.
Tokyo plans to make the planes to support their fleet, with 147 in-house or order. South Korea and Australia are also flying to the F-35 in the Pacific, and Singapore has said it wants to buy aircraft.
Specifically, issues related to the aircraft's supply chain remain an obvious concern, as maintenance costs for the F-35 are estimated at more than 1 trillion dollars over the 60-year life cycle, according to GAO estimates.
"The F-35 aircraft performance does not meet the requirements for military aviation – that is, planes can not carry out as many missions or fly as often as needed," GAO revealed. "This is less than the desired fulfillment of aircraft largely due to the lack of spare parts of the F-35 and the difficulties in steering and moving parts around the world."
The Pentagon and Lockheed Martin said they work with Gao to implement the specific recommendations outlined in their latest report.
"The Department worked with the Government Accountability Office for this F-35 Maintenance Report. The Department agreed with all eight recommendations of the report and gave a concrete, official response to everyone as explained on pages 69-72 of the" Spokesman Department Lieutenant Colonel Mike Andrews, in a statement to CNN.
Lockheed Martin also said that "it is taking aggressive measures to build capacity in the supply chain, reduce supply chain costs, and improve partial availability, to reduce maintenance costs while increasing preparedness ".
"We invest, we take aggressive action and cooperate with the government and our supply base in order to achieve price reduction targets, and we are also improving the willingness to fulfill the Pentagon's 80 percent Pentagon mission," the company said in a statement.
CNN Ryan Brown contributed to this report.