THE RPTR FLT INSTRUCTOR AND HIS STUDENT GOT TOO LOW ON A SIMULATED ENG FAILURE APCH AT NIGHT AND COLLIDED WITH A TREE BRANCH AS THEY MADE THEIR WAY TO AN OTHERWISE UNEVENTFUL LNDG.

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AT APPROX XA00; I WAS CONCLUDING A PERIOD OF LNDG PRACTICE WITH AN UNRATED STUDENT PLT. IT HAD BEEN DARK FOR ABOUT 25 MINS. THERE WAS A NEARLY DIRECT XWIND OUT OF THE NW AT ABOUT 8-10 KTS AT THE SURFACE AND WE WERE IN THE L PATTERN FOR RWY 23; WHICH UNICOM HAD DESIGNATED AS ACTIVE. THE APCH TO RWY 23 HAS A TALL SET OF PWRLINES ABOUT 1/3 MI FROM THE THRESHOLD AND A STAND OF TREES TO THE L OF THE APCH PATH; JUST BEYOND THE PWR LINES. SINCE THE STUDENT HAD MASTERED THE XWIND LNDGS; I INSTRUCTED HIM TO CUT THE PWR ABEAM THE NUMBERS ON THE DOWNWIND LEG AND PERFORM A SIMULATED EMER LNDG. I REMINDED HIM TO CONSIDER THE HEADWIND HE WOULD HAVE ON HIS BASE LEG AND THAT HE SHOULD START HIS TURN TO THE RWY CLOSE ENOUGH TO MAKE THE LNDG; AND TO ONLY APPLY FLAPS WHEN HE WAS ASSURED HE COULD COMPLETE THE GLIDE TO THE RWY. THE STUDENT PULLED THE CARB HEAT ON AND THE THROTTLE CLOSED ABEAM THE THRESHOLD AND WAITED 10-15 SECONDS TO BEGIN TURNING TO THE L-HAND ARC TOWARD THE RWY. HE BEGAN TO DEPLOY 10 DEGS OF FLAPS AS HE WAS 90 DEGS TO THE RWY AND I ADVISED HIM NOT TO USE FLAPS UNTIL HE WAS ASSURED OF MAKING THE RWY. HE THEN RETRACTED THE FLAPS PRIOR TO THEM REACHING 10 DEGS. AS HE CONTINUED THE TURN TOWARD THE RWY; I SENSED WE WERE SLIGHTLY LOW AND LOOKED TO THE R AND CONFIRMED THAT WE WERE INSIDE THE PWR LINES. THE STUDENT TURNED ON THE LNDG LIGHTS ABOUT THE TIME THE VASI PANELS BECAME READABLE; AND I THEN SAW THAT WE WERE LOWER THAN I HAD EXPECTED. AS MY HAND MOVED TO ADVANCE THE THROTTLE; I SAW THE IMAGE OF A TREE BRANCH PASS TO THE L OF THE NARROW LNDG LIGHT BEAM; THEN HEARD A BRANCH STRIKE THE L SIDE OF THE ACFT. I TOOK OVER THE LNDG AND THE REMAINDER OF THE LNDG WAS UNEVENTFUL. ONCE CLR OF THE RWY; I INSPECTED THE ACFT FOR DAMAGE AND DISCOVERED AN 8- 9 INCH WIDE X 1 INCH DEEP DENT IN THE L WING LEADING EDGE; JUST OUTBOARD OF THE STRUT. CONTRIBUTING FACTORS WERE: DARKNESS; A SLIGHT DELAY BY THE STUDENT IN TURNING TOWARD THE RWY; PREMATURE APPLICATION; THEN RETRACTION OF FLAPS; A CONSIDERABLE HEADWIND ON THE BASE LEG; 2 OBSTACLE SETS (LIT PWR LINES AND THE UNNLIT TREE STAND); A NONSTANDARD (SHORT EMER) APCH PATH THAT BROUGHT US OVER THE TREES; AND LATE IDENT OF A TOO LOW ON FINAL APCH CONDITION.