New York property developer pilot radioed air traffic control twice to ask permission to descend before falling unconscious at controls

Larry Glazer descended to 25,000 feet and had been given clearance to lower to 20,000 but air traffic controllers lost contact soon after

Jane and Larry Glazer, whose small plane crashed off the coast of Jamaica yesterday (YouTube/WXXI)

The pilot of a single-engine plane that crashed off the east coast of Jamaica had twice asked traffic control - before they lost contact - if he could reduce his altitude and had indicated that there was a problem with the aircraft.

Larry Glazer was flying a turboprop Socata TBM700 plane, with his wife Jane as passenger, from New York yesterday when they overran their Florida destination by 650 miles.

The couple are thought to have lost consciousness during their journey, with Mr Glazer slumped over the controls, before the small jet came down 14 miles northeast of the Jamaican town of Port Antonio, killing them both.

It has been suggested that the passengers may have experienced hypoxia or low levels of oxygen in the blood, which a Canadian army captain, Jennifer Stabnyck, told the Guardian.

In a recorded radio conversation between prominent real estate executive Mr Glazer and air traffic control, he had asked to descend his height – a request that had been granted. However, contact was lost soon after.

According to the Associated Press, the recording hears Mr Glazer say: “We need to descend down to about [18,000 feet]. We have an indication that's not correct in the plane.”

The controller told him to fly at 25,000 feet. “We need to get lower,” Mr Glazer replied, to which the controller said: “Working on that.”

Members of Jamaica's Marine Police return to port after conducting a search (Reuters)

Mr Glazer descended to 25,000 feet, when the controller cleared them for a descent to 20,000 feet – a command recognised by the pilot though he never made it down to that height. The controller asked Mr Glazer to respond but there was no reply.

The couple had taken off at 8.45am local time and controllers made their last contact at 10am.

The plane penetrated Cuba’s airspace as it travelled south, with two scrambled US F-16 fighter jets that has followed it trailing off before reaching the island nation.

Cuba reportedly fully co-operated with its diplomatic opponent, sending its own jets to follow the private plane and also allowing a US Coast Guard C-130 aircraft to go through its airspace and did not consider the Glazers' jet to be a violation, according to CNN.

US fighter pilots can be heard discussing Mr Glazer’s condition as they followed the Socata jet.

“I can see his chest rising and falling right before I left,” one said, in a recording.

“It was the first time we could see that he was actually breathing. It may be a deal where, depending on how fast they meet them, he may regain consciousness once the aircraft starts descending for fuel.”

The route of the that plane crashed off the island of Jamaica (Universal News And Sport)

No wreckage has yet been found and search teams are combing the waters for any survivors and it is still unknown if there were any more people on the plane.

Larry and Jane's son Rick Glazer confirmed his parents were licensed pilots.

Jamaica dispatched two aircraft and a dive team, Major Basil Jarrett of the Jamaican Defense Force said, while a US Coast Guard cutter is expected to join today.

Mr Basil added: “An oil slick indicating where the aircraft may have gone down has been spotted in the area where we suspect the crash took place.”

Real estate CEO Mr Glazer is described by his company Buckingham Properties as spending “some of his spare time on the ground – gardening around his house with his wife, Jane; and some in the sky – flying his plane. Larry serves as President of the TBM Owners and Pilots Association.”

Additional reporting by Associated Press