PROP SPINNER BREAKS OFF SMA WHILE AT CRUISE.

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MY INST INSTRUCTOR AND I; FLYING MY SMA FROM 48V VFR TO APA UNDER THE CTL OF DENVER APCH CTL. WE WERE GOING TO DO SOME INST APCHS INTO APA. WHILE IN LEVEL FLT AROUND 8000 FT; 22 IN MP; 2450 RPM; I LOOKED DOWN BRIEFLY TO LOOK AT THE CHART WHEN I HEARD A 'THUMP' AND BRIEFLY SAW SOMETHING HIT THE WINDSCREEN ON THE L SIDE. I THOUGHT WE HAD EXPERIENCED A BIRD STRIKE. WE IMMEDIATELY CHKED AT INSTS AND FOUND THAT EVERYTHING WAS NORMAL. WE DID 2 APCHS WITHOUT INCIDENT AND LANDED AFTER THE SECOND APCH. UPON LNDG; I MIGHT HAVE PULLED TOO MUCH PWR AND THE ENG QUIT; WE PULLED OFF TO THE TAXIWAY; I WASN'T ABLE TO RESTART THE ENG. MY INSTRUCTOR; GOT OUT; ATTACHED THE TOW BAR AND DISCOVERED THAT THE SPINNER HAD BEEN DAMAGED AND 2 NICKS WERE ON ONE OF THE PROPS. WE TOWED THE PLANE TO A TIE-DOWN SPOT AND L IT THERE. IN RETROSPECT; I BELIEVE WE SHOULD HAVE LANDED AFTER THE FIRST APCH. IN MY PREFLT; I DID NOTICE THE SMALL CRACK IN THE SPINNER BUT HAD BEEN TOLD BY MY MECH THAT IT WAS NOT A PROBLEM. I AM NOT SURE IF IT FAILED BECAUSE OF THE CRACK OR IF WE COULD HAVE HIT A BIRD.