American Airlines Flight 550 was headed to the United States East Coast city of Boston. After the captain was stricken, the first officer landed the plane in Syracuse, 500km short of its destination, with 147 passengers and five crew members onboard, spokeswoman Andrea Huguely said.
Before the flight landed, the first officer had called the airport tower and said, "American 550. Medical emergency. Captain is incapacitated." He requested a runway to land on.
In the recording of his exchange with the tower, he expresses concern over whether ambulance medics can get on the plane quickly.
Those on board knew something was wrong when a "quivering" voice came over the intercom, alerting them the pilot was sick, passenger Peter McSwiggin said.
A replacement crew was sent to Syracuse and the plane, an Airbus A320, landed in Boston.
Aviation experts said there was never any danger to passengers because pilots and co-pilots are equally capable of flying the aircraft.
Former airline pilot John Cox, an aviation safety consultant, said when one pilot becomes unable to fly the other will rely on help from the plane's automated systems and get priority treatment from air traffic controllers.
Captains and co-pilots usually take turns flying and doing takeoffs and landings, said former airline pilot James Record. "The advantage to that is the co-pilot gets an equal amount of experience and the captain gets to see how the other guy flies."
Record noted that the co-pilot remained calm. "He was doing what he's trained to do - fly the plane. He was probably more concerned with the health of his buddy, his crew member," than his ability to fly.
Airline pilots must pass physical exams every 12 months, every six months for captains 40 or older.
According to the Federal Aviation Administration, seven pilots for U.S. airlines and one charter pilot have died during flights since 1994.
