DURING A SPECIAL VFR CLRNC TO A NON INST APCH EQUIPPED ARPT; FLC OF AN LTT CPR JET BECAME DISORIENTED DUE TO LACK OF KNOWLEDGE IN OPERATING THE ACFT NAVIGATIONAL EQUIP.

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