The Coast Guard said a small, private plane, a Cessna 421C, sunk into the Gulf of Mexico. Crews flying over the site of the crash gave did not see any indication that the pilot, Dr. Peter Hertzak, survived.

The pilot was identified by Slidell Airport as Dr. Peter Hertzak of Slidell, La., reported NBC. The plane eventually ran out of fuel and crashed into the water, reported Reuters.  It slowly began to sink to the ocean floor. Authorities believe that Hertzak was unconscious and was the only person on board the plane.

Hertzak took off from Slidell Airport en route to Sarasota, Fl. when air traffic controllers lost contact with him, reported Reuters. He was approximately 28,000 feet over the Gulf waters and began flying around in circles for several hours on Thursday at approximately 9:30 a.m.

Two F-15 fighter jets were quickly dispatched to intercept the plane as a potential threat when Jacksonville Air Traffic Control Center asked the Air Force to check on the plane, reported MSNBC.  However, officials were still unable to get in contact with the suspicious aircraft, as it circled the Gulf of Mexico. They believe the Hertzak had been incapacitated.

As the fuel in the small plane began to dwindle, the plane went down into the waters below at around noon, said Coast Guard Chief John Edwards, according to the Associated Press. The plane appeared to land right side up on the surface of the water. Monitoring planes, however, did not see any sign of life as it began to sink.  

The Coast Guard dispatched an HC-144 Ocean Sentry from Mobile, Ala., an MH-60 Jayhawk helicopter and the Coast Guard Cutter Coho, reported MSNBC.

The situation is pretty dynamic right now, said petty officer Elizabeth Boderland of the Coast Guard at the time of the incident.

Bill Huete was a mechanic who worked on the downed aircraft in the past and met Hertzak,who worked as an OB-GYN.

I met him years ago when he was looking to start flying again and bought this plane, said Huete, reported the Associated Press. He flew by the book and he didn't scrimp on maintenance.

While the cause of the crash is still under investigation, it is possible he suffered from hypoxia, or a lack of oxygen.

As the pilot was in the climb, the cabin was not pressurizing, speculated Stephen Aynaard, ABC News aviation consultant, so there was not sufficient oxygen to keep him conscious.