( CNN ) -- A small plane with an unresponsive pilot sank in the Gulf of Mexico on Thursday after circling above the ocean for more than two hours , then crashing , the U.S. Coast Guard reported . The twin-engine Cessna 421 remained afloat with its tail sticking out of the water for some time before it sank Thursday afternoon , said Petty Officer Elizabeth Bordelon , a Coast Guard spokeswoman . No remains have been found , and the Coast Guard still considered its operation an active search and rescue . There was no sign of the pilot , Bordelon said . The plane went down about about 120 miles west of Tampa , Florida , at 12:08 p.m. after circling the eastern Gulf for more than two hours , said Chief Petty Officer John Edwards , a Coast Guard spokesman . The crew of a Coast Guard search-and-rescue plane watched as the Cessna made what appeared to be a soft landing , Edwards said . A Coast Guard plane from the Tampa area and the cutter Coho were still taking part in the search Thursday evening , and the Coho was expected to remain at the scene overnight , Bordelon said . The plane took off from Slidell , Louisiana , en route to Sarasota , Florida , with a single pilot on board . It had been circling at an altitude of about 28,000 feet , a Federal Aviation Administration source told CNN . The Air Force began monitoring the plane after noticing it flying erratically over the Gulf of Mexico on Thursday morning , and planes sent up to investigate it reported the Cessna 's windows were either iced or fogged over , Edwards said . Pilots at the Slidell Municipal Airport said the victim was Dr. Peter Hertzak , a cosmetic surgeon who was well known in the area . `` I 've lost a dear friend , just a great guy , '' pilot Bill Huete told CNN affiliate WWL-TV . `` Super doctor and just a regular guy that would do anything for anybody . '' Hertzak was the head of the Hertzak Laser Center , which specializes in liposuction and cosmetic surgery . He had more than 30 years of experience , according to the center 's website . The Coast Guard plane and two F-15s from the North American Aerospace Defense Command were still watching the Cessna before it went down , the Air Force and Coast Guard reported . The Coast Guard said an investigation was under way . But aviation expert Miles O'Brien told CNN the circumstances point toward a possible loss of cabin pressure in the eight-seat , propeller-driven aircraft . `` At 28,000 feet , you do n't have an awful lot of useful consciousness without the support of oxygen or being in a pressurized aircraft , '' said O'Brien , a former CNN correspondent . If a lone pilot is incapacitated at that altitude , `` there are n't a lot of options for resuscitating him and getting him back flying . '' Fellow pilot Patrick Quigley told WWL that Hertzak maintained his plane meticulously and spared no expense to keep it in `` tip-top shape . '' Quigley said Hertzak was an accomplished pilot and that the flight should have been routine , `` but when something goes wrong , obviously you have nowhere to go when you 're out over the ocean . '' In 1999 , a private jet carrying golfer Payne Stewart and five others crashed after apparently losing cabin pressure `` for undetermined reasons '' after takeoff from Florida , the National Transportation Safety Board found . Fighter pilots were sent up to intercept Stewart 's plane after controllers lost contact with it , and they reported its cockpit and cabin windows were frosted over . The plane flew more than halfway across the United States , apparently on autopilot , until it crashed in a South Dakota field . CNN 's Dave Alsup , Rick Martin , Devon Sayers , Aaron Cooper , Todd Spoerry , and Joe Sutton contributed to this report .
NEW : Friends identify the pilot as a well known cosmetic surgeon in the area . The plane has crashed , no pilot found , the Coast Guard reported . The Air Force noticed the plane flying erratically this morning . Interceptor pilots reported the plane 's windows were fogged over .