US planemaker Boeing used an unusual substitute for passengers to test its in-flight wi-fi system - potatoes.Passenger seats on a decommissioned plane were loaded with huge sacks of the tubers for several days as signal strengths were checked.The company's researchers say that potatoes "interact" with electronic signals in a similar way to humans.The technique also took advantage of the fact that spuds - unlike humans - never get bored.Boeing's engineers did a number of tests to ensure that pas...