The plane was "taxing"?

Anyone who has flown on a plane is probably familiar with this sense of the word of taxi: "to cause (an aircraft) to move along the ground under its own power, esp before takeoff and after landing" (Collins).

Much like the verb "to ski", I think the past tense should have two i's.  (Collins agrees: "Word forms: taxies, taxiing, taxying, taxied".)