SAO PAULO, Brazil — A Brazilian Air Force investigation has concluded that a switched-off transponder contributed to a plane crash that killed 154 people in 2006, local media reported today.

The Estado de Sao Paulo and Folha de Sao Paulo newspapers said that Air Force investigators determined that the two American pilots of a New York-based executive jet had inadvertently placed the transponder and the collision-avoidance system on standby before colliding with a jetliner on Sept. 29, 2006.

The newspapers said the Air Force also concluded that flight controllers failed to alert the pilots that they were on a collision course and failed to notice that the transponder was turned off. Calls to the Air Force for comment went unanswered today. The report is scheduled to be released formally on Wednesday.

The Boeing 737 operated by Gol Linhas Aereas Inteligentes SA collided over the Amazon rain forest with an Embraer Legacy 600 executive jet owned by ExcelAire Service Inc. of Ronkonkoma, New York.

Everyone aboard the Gol aircraft was killed, while the Legacy landed safely.

Four flight controllers on duty at the time of the accident and the two U.S. pilots – Joseph Lepore of Bay Shore and Jan Paladino of Westhampton Beach have been indicted on charges similar to involuntary manslaughter that carry up to three years in prison.

The pilots have denied turning off the transponder and have said they were flying at an altitude designated by the air controllers.

“The transponder issue is a distraction from the true cause of the accident, which is an air traffic control system that put two airplanes on a collision course for about an hour,” David Rimmer, ExcelAire’s executive vice president, said today.

He said Brazilian flight controllers failed to “recognize the transponder failure and to provide increased separation between the two jets, as required by international aviation regulations.”

“We have no proof of how the transponder was turned off and no evidence to suggest it was inadvertently turned off by the pilots” Rimmer added, complaining that the Air Force “relied on theories rather than conducting in-depth testing of the equipment.”

The Air Force investigation, separate from court actions, is meant to determine the causes of the accident and recommend measures to help avoid similar tragedies, the two newspapers said.

The American pilots were allowed to leave Brazil after agreeing to return if courts summon them.