Blamed initially on 'engine failure,' it emerged on Tuesday that a government jet carrying Serbia's president to Italy last week was forced to turn back when the co-pilot spilled coffee on the instrument board.

Advisers to President Tomislav Nikolic described being "thrown around the cabin" when the plane — a 34-year-old French-built Falcon 50 — began tumbling through the air on Friday.

The plane landed safely back in Belgrade, but Nikolic was forced to cancel his official visit to meet Pope Francis in the Vatican, and his advisers put the incident down to yet another malfunction on the ageing, incident-prone aircraft.

One adviser told Reuters that she would "never step foot on that plane again," saying the fall had lasted "for what seemed like an eternity."

An investigation determined that the co-pilot, Bojan Zoric, had spilled coffee on the instrument board "due to ongoing turbulence."

"I began wiping the board and accidentally activated the 'emergency slat' button," which automatically turned off the automatic pilot and the plane began losing altitude, Zoric said in the report by Serbia's Civil Aviation Directorate.

The pilot took over command, managed to pull the plane up and sought permission to turn back to Belgrade, Zoric added. He said that one of the engines then stopped working but was restarted on the way back to the airport.

The Directorate temporarily suspended Zoric's license on Monday.