Oops:
The cause of the communications equipment problem that caused a United Airlines flight out of O'Hare International Airport to make an unscheduled stop in Toronto this week was the pilot's spilled cup of coffee, Canadian officials said.
The flight to Frankfurt, Germany was diverted after the pilot dumped a cup of coffee on the plane's communication's equipment. The unwanted liquid triggered a series of emergency codes, including one for a hijacking, according to Transport Canada, the agency that regulates transportation in Canada.
News reports today have mentioned "communications equipment," but it should be clear that they meant the airplane's transponder. Every airplane flying on an instrument flight plan (which includes every airplane flying above 5,500 m) broadcasts its altitude along with a discrete base-7 code number. The numbers from 7000 to 7777 are reserved for emergencies. So in the pilot's defense, I have to ask why the transponder started sending out 7000-series codes when it got wet. You'd think it would just shut off? And can you imagine the scene at the local TRACON when "United 940 Heavy" started rapidly changing its call sign? What would that look like on the scope?
By the way, the important 7000 codes (7500, 7600, 7700) cause TRACON scopes to go nuts. That would have been exciting to watch, I'm sure.