Story highlights Phoenix-to-Boston flight with 147 passengers and five crew members diverted to Syracuse, New York

Passenger: If not for the co-pilot's "cool head, it might have been more disastrous"

(CNN) Medical emergencies are rare, but hardly unprecedented in commercial flights.

It's far less common when they involve the plane's pilot -- and that pilot dies.

That's what happened Monday on an American Airlines flight between Phoenix and Boston.

Captain Michael Johnston, 57, was piloting the plane when he fell ill somewhere en route. The co-pilot landed the jet safely.

Crew members "took extraordinary care of Mike, each other and our customers," airline CEO Doug Parker said in a statement sent to employees.

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