A coffee spillage in the cockpit of an airliner flying over the Atlantic Ocean forced the plane to turn back and land in Ireland.
The hot liquid damaged an audio control panel, producing an electrical burning smell and smoke, an accident report revealed.
It created “significant communication difficulty” for the pilots flying the Condor aircraft, the Air Accidents Investigation Branch (AAIB) said.
The incident happened on February 6 and resulted in the Airbus A330 flight from Frankfurt in Germany to Cancun in Mexico being diverted to Shannon.
The smoke stopped and the fumes did not result in injuries to any of the 11 crew or 326 passengers on board.
Diversions typically cost airlines between £10,000 and £80,000 depending on the size of the aircraft and where it diverts to, according to the Civil Aviation Authority.
The report found the 49-year-old captain had put his coffee cup on a tray table – where objects are “vulnerable to being knocked over” – despite Airbus recommending pilots use the cup holders provided.
The AAIB said the small size of cups used by Condor “generally discouraged” use of the holders as it was difficult to grasp them.
Investigators also noted putting a lid on the cup may have reduced the amount of coffee spilled.
Condor responded to the accident by ensuring cup lids are provided on all flights, reminding pilots to be careful with liquids and supplying cups that are an appropriate size for cup holders.
A spokeswoman for the airline, which is a subsidiary of Thomas Cook Group, said: “Flight DE2116 from Frankfurt to Cancun on February 6 2019 diverted to Shannon airport as a precautionary measure due to a minor amount of smoke in the cockpit after a liquid spillage.
“After the aircraft was fully inspected and repaired by our team of engineers, the flight continued via Manchester due to the legal operating hours of the crew.
“We have comprehensively investigated this incident and reviewed the procedures of liquids in the cockpit.
“Our crews were reminded of (the need for) careful handling as well as to use appropriate containers for their water or coffee.
“We apologise for any inconveniences the diversion might have caused to our guests.”