MILWAUKEE – A medical transport plane carrying six members of an organ transplant team went down Monday afternoon in Lake Michigan shortly after the pilot signaled an emergency, authorities said. Rescue teams were searching for any survivors.

Nearly three dozen divers were looking near debris and an oil slick in about 20 feet of water, Milwaukee Fire Chief Doug Holton said.

The pilot of the Cessna Citation issued a distress signal within five minutes of taking off at 4 p.m. from General Mitchell International Airport in Milwaukee, Federal Aviation Administration spokesman Tony Molinaro said. The plane was headed for Willow Run Airport near Detroit, a 42-minute flight, Molinaro said.

The plane dropped off radar screens just after the pilot requested to return to the airport, and authorities notified the Coast Guard, Molinaro said.

Coast Guard searchers found what they believe was the plane around 4:20 p.m., about 20 minutes after being notified, Petty Officer David Warfel said. The debris was found about six miles northeast of Milwaukee, Molinaro said.

There has been no sign of the four passengers or two crew members, Molinaro said.

The plane was leased by the University of Michigan Health System in Ann Arbor, according to a university statement. The team was returning from Milwaukee with unspecified organs for transplant to a patient in Michigan.

When health system officials learned of the crash, they notified the transplant team in Michigan to stop preparing the transplant candidate. The patient was in critical condition, the university said.

The university wouldn’t release any information on the patient, citing confidentiality.

The university identified those on the plane: Dr. David Ashburn, a physician-in-training in pediatric cardiothoracic surgery; transplant donation specialists Richard Chenault II and Richard Lapensee; pilots Dennis Hoyes and Bill Serra; and cardiac surgeon Dr. Martinus “Martin” Spoor.

“The thoughts of the entire university community are with the families of those involved this evening, and we take consolation in the fact that the team was on a mission to help another,” said Dr. Darrell A. Campbell, chief of staff of the University of Michigan Hospitals & Health Centers.

The plane is owned by Toy Air and based at Willow Run Airport in Ypsilanti, Mich.

Around 4 p.m. light rain was falling at the airport with winds at 12 mph, gusting to 22 mph, according to J.J. Wood, meteorologist the National Weather Service.

U.S. Coast Guard Capt. Bruce Jones said the water temperature was 57 degrees and survivors could live for 16 hours. He said they have not found any bodies.

“Our primary focus is on finding any survivors there may be from this incident,” he said.