NASHVILLE, Tenn. (AP) — A clean-energy advocacy group called for an investigation Tuesday after finding that the Tennessee Valley Authority bought two corporate jets, a Mercedes-Benz luxury helicopter and another plane in recent years.

The Southern Alliance for Clean Energy said the 2015 and 2017 model jets, 2013 model Style helicopter and 2015 turboprop airplane were worth $40 million new, though the helicopter was bought used.

TVA deemed the equipment necessary to meet customers and stakeholders and pursue economic development by attracting companies to the region, another part of the utility's mission.

Alliance executive director Stephen Smith called the aircraft purchases "the very definition of corruption of the TVA mission." The group did not specify who should investigate, but called for oversight from TVA's inspector general and Congress.

"Buying extravagant jets and helicopters is a hijacking of the TVA Act, whose stated purpose is to protect the residential customers, not buy flashy toys for millionaire executives or cut backroom deals with private industry," Smith said in a news release.

Debbie Dooley, who helped found the ongoing national Tea Party movement and is president of Conservatives for Energy Freedom, said the purchases show TVA Bill Johnson needs to be replaced.

Johnson, the highest-paid federal employee in the nation, is receiving a compensation package of more than $6 million, including retirement and other benefits. The TVA board has said Johnson's pay is still low compared to salaries of utility executives not in public service.

Elder Jimmie Garland, vice president of the Tennessee State Conference of the NAACP, said the findings show the need for independent oversight of the nation's largest public utility.

TVA spokesman Jim Hopson responded that private aircraft are the only safe, timely option across TVA's 80,000-square-mile, seven-state service area, which largely lacks commercial flights.

Operating the modern jets costs just 7 percent more than the older turboprops, with improved safety and performance, Hopson said.

The helicopter can hold more passengers for economic development activities, Hopson said.

Other TVA helicopters support inspection, maintenance and repairs of TVA's 16,000-mile transmission system.

TVA services Tennessee and parts of Georgia, Alabama, Mississippi, Kentucky, North Carolina and Virginia.

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