A co-pilot suddenly lost consciousness during an El Al flight to Venice on Thursday, forcing the captain to make an emergency landing in Dubrovnik, Croatia.

El Al Flight 289 had taken off from Ben-Gurion International Airport before noon with 98 passengers on board. The co-pilot was treated on the plane by one of the passengers, a doctor.

El Al Chief Executive David Maimon ordered a special private plane crew to fly the passengers to Venice and bring the co-pilot back to Israel. Maimon spoke to the co-pilot, who was feeling better.

Maimon said the captain and the entire crew behaved calmly, helped take care of the co-pilot and ensured that the Boeing 737 landed safely.

Airline sources who spoke to Haaretz rejected the possibility that the co-pilot passed out due to fatigue. Just this week, El Al pilots went on a surprise slowdown seeking a new labor agreement. One of the issues was fatigue.

The sources said El Al pilots undergo medical examinations every six months. They said the co-pilot could have suffered a heart problem or an illness linked to something he ate before the flight.