United flight 1996 from Chicago O’Hare to San Juan was delayed three hours when the captain spilled coffee in the cockpit. The Airbus A321neo was already taxiing out when this happened, and had to return to the gate.

That delayed the return flight from San Juan back to Chicago O’Hare by nearly three hours as well. Spilling much more than a little bit in the cockpit would certainly have cancelled the flight. Not only does the spill need to be cleaned, but whatever was spilled on needs to be inspected as well.

Coffee is especially bad because it’s hot, acidic, and often has sugar and cream which can leave a sticky residue. That could mean inspecting:

• Control panels & switches: The center pedestal (throttles, ENG START, radio tuning units, ECAM control panel) and overhead panel are exposed. Any spill on them requires drying, cleaning and functional checks.

• Avionics / electrical systems: The avionics bay is directly below the cockpit floor on an Airbus A321. Liquids can seep through gaps around the pedestal and drip onto avionics racks.

• Flight control levers: (throttle, flaps, spoilers, gear) Coffee into the throttle quadrant or flap lever area would require inspection.

• Circuit breakers & wiring bundles: I think that the A321neo has breaker panels along the sidewalls? Some pilot and mechanic readers can confirm.

• Sidestick controllers: Airbus has sidesticks on the side consoles, which also have storage and cupholders. A spill there could drip into the sidestick base.

Airlines typically require a mechanic to open the affected panel, clean it, dry it, and sometimes run functional checks before release. Depending on where it landed, it might even trigger a requirement to replace switches or modules.

Pilots routinely drink coffee or water in the cockpit, even during taxi. The sterile cockpit rule applies below 10,000 feet (taxi, takeoff, landing), but that governs conversation and tasks not essential to flight, not drinking. Handling a beverage is normal. The unusual part is the spill, especially one that reaches sensitive avionics or controls.

The risks here aren’t theoretical. In 2019, a Condor Airbus A330 from Frankfurt to Cancun diverted when the captain spilled coffee on their audio control panel, which overheated, smoked, and led to the failure of the first officer’s audio control paenl as well. This led to a safety recommendation of lidded cups and the use of cupholders.

In 2011, a United Boeing 777 from Chicago O’Hare to Frankfurt accidentally squawked 7500 and 7600 (hijack and lost communications) after coffee spilled on the pedestal and the pilots were dealing with communication and navigation issues. The flight diverted to Toronto.

We’ve also seen multiple Airbus A350 incidents, such as Delta diverting to Fairbanks in January 2020 after coffee spills on the engine start panel preceded in-flight engine shutdowns.

It occurs to me that there’s one benefit to American Airlines never improving its onboard coffee (they still use Fresh Brew – which was derided at United as Fresh Poo before they replaced theirs with the excellent Illy). You’ll have fewer pilots at American drinking the airline’s coffee in the cockpit. That’s great for ops! On the other hand, it also means more flight delays as pilots stop at Starbucks in the terminal rather than rely on what’s served onboard.

Coffee isn’t even the strangest reason why United had to delay or cancel Airbus A321neo flights. When they first received the planes the no smoking signs did not turn off, by design and United forgot to ask for a regulatory exemption because smoking hasn’t been allowed onboard in decades.