BE90 FAA INSPECTOR AND FO IN R SEAT; TAKING CHK RIDE; HAD AN NMAC WITH A C172 ON APCH TO RWY 18 AT IKV.

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RPTR WAS FLYING R SEAT IN A PART 135 CHK RIDE. FINAL ITEM IN THE CHK RIDE WAS NDB-A CIRCLE 18 AT IKV. CHK PLT WAS FAA INSPECTOR (POI) FOR THE RPTR'S COMPANY. AIRPLANE #1 WAS ON THE NDB COURSE INBOUND AND FAA INSPECTOR IN L SEAT MADE RADIO CALLS. ACFT #2 RPTED SHORT FINAL RWY 18 WHEN ACFT #1 WAS APPROX 2 MI OUT. FAA INSPECTOR 1) 'FAILED' AN ENG; 2) SAW ACFT #1; AND 3) ALLOWED RPTR TO LIFT 'HOOD' ALL AT ABOUT THE SAME TIME. ACFT #1 TURNED R (NORTHERLY) AND THEN TURNED BASE. FAA INSPECTOR RPTED BASE LEG AND ASKED FOR ACFT #2'S POS. THERE WAS NO RESPONSE AND THE (FALSE) ASSUMPTION WAS THAT ACFT #2 WAS ON THE GND. ACFT #1 PROCEEDED TO LAND AND ON ROLLOUT THE PLT OF ACFT #2 RADIOED THAT WE HAD COME RIGHT OVER HIM ABOUT 25 FT HIGHER AND THAT OUR WAKE TURB HAD JUST ABOUT PUT HIM DOWN. RPTR NEVER SAW ACFT #2 DURING ALL THESE EVENTS. ON THE GND; THE PLT OF ACFT #2 SAID THAT HE WAS PRACTICING SHORT FIELD TKOFS AND WAS VERY SLOW ON FINAL. BEFORE THIS OCCURRENCE; DURING THE SAME FLT OF ACFT #2; ANOTHER PLT ADVISED THE FBO MGMNT AT IKV THAT ACFT #2 WAS 'FLYING LARGE PATTERNS.' PLT (POI) OF ACFT #1 SAW ACFT #2 WHEN ACFT #2 WAS IN A POS THE POI THOUGHT WOULD HAVE ACFT #2 ON THE GND LONG BEFORE ACFT #1. DURING THE ENSUING 'ENG FAILURE' AND MANEUVERING; ACFT #2 WAS LOST TO SIGHT. AS ACFT #1 BANKED TO TURN FINAL; POI ASKED WHETHER RPTR SAW ACFT #2. I HAD NOT. POI COMMENTED THAT HE MUST BE CLR OF THE RWY BECAUSE THERE WAS NO ONE ON THE RWY. GET AND KEEP PATTERN TFC IN SIGHT. BE AWARE OF SPD DIFFERENTIAL.