A PLT RECEIVING AN INSTRUCTOR'S CHK RIDE DID AN UNINTENTIONAL LOW APCH AND AN ACFT TIRE CONTACTED A VEHICLE ROOF ON SHORT FINAL.

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AS THE ASSISTANT CHIEF OF A PART 141 SCHOOL; I WAS CONDUCTING AN ANNUAL PART 141 INSTRUCTOR CHK RIDE. I ASKED FOR A SIMULATED EMER APCH AND LNDG FROM PATTERN ALT. THE CFI FLYING THE AIRPLANE WAS TO PERFORM THE MANEUVER AND INSTRUCT AT THE SAME TIME. I NOTICED THAT THE TURN TO THE RWY WAS LATE BUT BY HOLDING FLAP EXTENSION TO 10 DEGS AND FLYING A TIGHT PATTERN; IT APPEARED WE WOULD MAKE THE RWY. A ROAD CROSSES AT THE END OF THE RWY AND AS WE PASSED OVER THE ROAD; A VAN WAS DIRECTLY BENEATH US AND THE R TIRE CONTACTED THE ROOF OF THE VAN. I FELT A BUMP BUT DID NOT SEE THE VEHICLE WHICH CAME FROM THE R SIDE. THE LNDG WAS UNEVENTFUL. THE ACFT SUSTAINED NO DAMAGE BUT SUBSEQUENTLY A VAN CAME TO THE REFUELING PUMPS AND WE WERE SHOWN A DAMAGED SPOT ON THE ROOF OF THE VAN WHERE THE TIRE HIT. THERE WERE NO INJURIES. THE CAUSE OF THIS INCIDENT WAS A POOR APCH PATTERN FOLLOWED BY A LOW AND SLOW APCH ON FINAL LEADING TO A SINK RATE GREATER THAN EXPECTED. I SHOULD HAVE INTERVENED AND CALLED FOR PWR AND A GAR AS SOON AS I NOTICED A POOR PATTERN AND NOT ALLOWED THIS SIMULATED MANEUVER TO TURN INTO A REAL INCIDENT.