On this continuum, the level of professional skepticism moves from something less than complete trust, to a neutral mind-set, to presumptive doubt, and all the way to complete doubt. The appropriate level of skepticism to apply is initially determined only after a careful and rigorous risk assessment.
1 The longest flying aircraft flying from Kansas City, MO to Cancun, Mexico during the 2009 year was a AirbusNdustrie's A319 flown by Frontier.  Back in 2009 there was just one airline company operating flights between Kansas City and Cancun.
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