ATLANTA (CBS/AP) — For the second time in three days, a passenger on board a commercial U.S. airlines flight died mid-air.

Delta Air Lines said a 57-year-old passenger was found dead aboard a flight from Nigeria to Atlanta.

Georgia Bureau of Investigation spokesman John Bankhead said an autopsy determined Aolatou Assani died of ovarian cancer.

Delta spokeswoman Susan Elliott said she was found unresponsive early Monday aboard Delta Flight 53, about an hour out of Atlanta and about 11 hours after it took off from Lagos.

FBI Special Agent Steve Emmett said the FBI was initially involved in the investigation because the woman died aboard an international flight.

On Saturday, a man from New York died of an apparent heart attack on an AirTran Airways flight from Las Vegas to Milwaukee, forcing the plane to make an emergency landing at Denver International Airport.

DIA airport spokeswoman Laura Coale said flight 776 was diverted to Denver and was met at the gate by an ambulance at about 2:50 a.m. The Denver Medical Examiner’s office said Stephen Enves, 64, of Elmhurst, N.Y., was traveling with his wife when he died. An autopsy is planned.

The airplane continued its flight to Milwaukee at about 6:30 a.m.

AirTran spokesman Christopher White said a passenger applied CPR and an automatic external defibrillator was used in attempts to save Enves’ life.

Enves was pronounced dead in Denver.

Similar incidents have occurred on flights en route to the New York City metropolitan region in the past two years.

Last June, a Continental Airlines captain died mid-flight on a trip from Brussels to Newark. The 60-year-old fell ill about 3 hours into the flight and apparently died of natural causes.

In February 2008, a woman on board a flight from Haiti to John F. Kennedy International Airport died after she reported having breathing problems. The plane was diverted to Miami, but the woman died before she could be taken to a hospital. Flight crew and doctors on board attempted to administer oxygen and CPR to the woman.

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