By Melissa R. Nelson
Associated Press

PENSACOLA, Fla. — A pilot flying a Cessna across the Gulf of Mexico stopped responding to radio calls including those from two F-15 aviators who flew alongside and monitored the plane for hours as it made a corkscrew path through the sky before crashing into the ocean Thursday, authorities said.

Coast Guard crews saw no signs that the pilot — the lone person aboard — survived. The plane landed right-side up on the ocean surface and had been floating right after the crash, said Chief John Edwards. However, the Cessna 421C later sank into the Gulf about 120 miles west of Tampa, Fla., in about 1,500 feet of water.

The plane was headed from Slidell, La., to Sarasota, Fla., and controllers lost contact with it about 9 a.m. EDT, said Federal Aviation Administration spokeswoman Kathleen Bergen. The plane went down about 12:10 p.m. and authorities were investigating but have released no information about what may have gone wrong.

The New Orleans National Guard jets were already on a mission over the Gulf when Jacksonville air traffic controllers asked the military if it could check on the plane that was orbiting near one of Eglin Air Force Base’s warning areas over the Gulf, Edwards said. The fighter jets caught up with the plane and reported that it was fluctuating between 25,000 and 35,000 feet and its windshield was iced over.

They could not hail the pilot, whom authorities have not identified.

Bill Huete, a mechanic at the Slidell Airport, said Dr. Peter Hertzak, an OB-GYN who worked in the community just northeast of New Orleans, was the only person who piloted the plane. Huete said the doctor’s wife told him her husband was flying the plane that morning.

Huete had worked on the plane for Hertzak and has known the doctor and his family for years.

“I met him years ago when he was looking to start flying again and bought this plane,” said Huete.

A computer-generated image provided by FlightAware, a private aviation flight path service, shows the plane traveling in several circles over the Gulf before going down. A C130 and a helicopter looked for debris from the submerged plane, said Coast Guard Petty Officer Elizabeth Borderland. A cutter would remain in the area all night, she said.

Huete described Hertzak as an excellent pilot. “He flew by the book and he didn’t scrimp on maintenance,” Huete said.

No one answered the door at an address listed for Hertzak and calls to the home rang unanswered. Hertzak’s office said any statement would have to come from his family and the Coast Guard said it wouldn’t release the name for 24 hours according to its policy. Several online public records showed Hertzak was 65 years old and that he was licensed as a private pilot by the FAA in 2008.

In 1999, a charter jet crash killed pro golfer Payne Stewart and four others and flew halfway across the country on autopilot before crashing in a pasture in South Dakota.

Everyone on board had apparently lost consciousness for lack of oxygen after a loss of cabin pressure, and the plane crashed after it ran out of fuel, investigators said.