(CNN) -- A 16-year-old who died Saturday on a Delta Air Lines flight bound for Atlanta had a rare preexisting medical condition and went into cardiac arrest, authorities in Spokane, Washington, said Monday.
Flight 128 left Seattle and made an emergency stop in Spokane on Saturday morning. Firefighters boarded the plane on the tarmac and found a physician and nurse on the flight trying to resuscitate the youth, Spokane Assistant Fire Chief Brian Schaeffer said.
Firefighters took over but after about 35 minutes of CPR he was pronounced dead, Schaeffer said.
The flight carried 258 passengers. "Everybody knew what we were doing," Schaeffer said. "Overall it was an emotional experience for all the passengers on board."
The Spokane Medical Examiner's office said Monday that the cause of death is listed as "pending" until further microscopic studies are completed. The office said the death "is thought to be a rare complication of a rare disease process. The manner of death is natural."
The youth was traveling with his mother to Atlanta for the holidays, Schaeffer said. His father is a soldier from the 16th Combat Aviation Brigade of the 7th Infantry Division out of Joint Base Lewis-McChord at Fort Lewis, Washington, a U.S. military official said. The family was going to join the father who'd gone ahead to a new base, the official said.
CNN is not releasing the youth's name because he's a minor.
Delta spokesman Michael Thomas said a new flight crew was brought in and the plane continued to Atlanta, landing Saturday night several hours after its original arrival time.