>> The Mars Climate Orbiter disintegrated due to an error introduced because its software used metric measures, while its ground crew used pound-force units.
There was an incident in 1983 where Air Canada Flight 143 ran out of fuel at 41,000 feet (12,500m) altitude [1] about half way through its flight. An investigation revealed that one of the cause was a conversion error between metric and non-metric units for the fuel loading calculation.