C172 N MODEL HAS DUAL MAGNETO FAILURE SHORTLY AFTER TKOF. ABLE TO RETURN LAND SUCCESSFULLY. MAINT INSPECTION FOUND LACK OF REDUNDANCY CAPABILITY WITH BOTH MAGNETOS TIED TO A SINGLE SHAFT.

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AFTER AN UNEVENTFUL PREFLT AND RUNUP IN A C172 I BEGAN A STANDARD TKOF ON RWY 29 AT BDR. THE CURRENT WINDS WERE APPROX 300 DEGS AT 11 KTS AS RPTED BY THE CTL TWR. THE TKOF ITSELF WAS UNEVENTFUL. AT APPROX 1000 FT MSL (900 FT AGL) THE ENG SUDDENLY LOST PWR TO APPROX 800-1200 RPM. AT THIS TIME AN EMER WAS DECLARED AND THE ACFT WAS TURNED BACK TO THE BDR ARPT. AFTER THIS WAS ACCOMPLISHED THE EMER CHKLIST WAS COMPLETED AS FAR AS APPLYING CARB HEAT; SWITCHING TANKS AND ENSURING A 'FULL RICH' MIXTURE. WE THEN PROCEEDED TO MAKE AN EMER LNDG WHICH WAS SUCCESSFULLY COMPLETED ON RWY 6. AFTER TAXIING CLR OF THE RWY THE ACFT WAS SECURED AND ALL THE OCCUPANTS EXITED THE ACFT UNHARMED AND THE APPROPRIATE INFO WAS GIVEN TO THE AUTHS. IT WAS THEN LATER DETERMINED THAT A DUAL MAGNETO FAILURE WAS THE CAUSE OF THE PWR LOSS. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR STATES THE ACTUAL CAUSE WAS THAT BOTH MAGNETOS ARE TIED TO A SINGLE SHAFT AND WHEN GEARS STRIPPED ON 1 SIDE THEN THEY WERE THROWN INTO THE OTHER ONE. SO MUCH FOR REDUNDANCY. THE MECHS CONTACTED THE FAA AND IT WAS INDICATED THAT THIS IS THE FIRST TIME THEY HAD HEARD OF SUCH AN INCIDENT. RPTR DOUBTS IT; HOWEVER. THIS WAS AN N MODEL 172.