The UK Air Accidents Investigation Branch says that, while Airbus recommends using the cup-holder, the size of cups used by the carrier on the route made lifting them from the holder difficult.
"This incompatibility generally discouraged use of the cup holder, despite the policy," it states, adding that the crew naturally tended to place cups on the fold-out table in front of them – making them "vulnerable" to being knocked over.
The coffee on the A330 captain's table was spilled, with a small amount falling on the left-hand audio control panel, which immediately malfunctioned and subsequently failed. Some 20min later the first officer's corresponding control panel also became hot and failed – although the precise reason for this was not clear.
VHF radio transmissions and public-address announcements were affected by the malfunctions and the captain chose to divert to Shannon, with the precautionary use of cockpit oxygen masks owing to electrical smoke emanating from the panel.
The end result was a diversion to Shannon.
The airline now provides lids for coffee served in the cockpit and "seeks" to find more appropriately sized cups.