A C172 INSTRUCTOR AND STUDENT; DEPARTING SNA; EXPERIENCED A PARTIAL LOSS OF ENG PWR; SPAWNING A RETURN TO SNA.

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ON NOV/MON/02; I WAS RECEIVING FLT INSTRUCTION IN A C172RG FOR MY COMMERCIAL CERTIFICATE. WE HAD EARLIER RECEIVED A CLRNC FOR A DEP IN CLASS C AIRSPACE FOR A L TURN TO 080 DEGS AFTER DEP. WIND WAS RPTED AS 230 DEGS AT 6 KTS. AFTER A NORMAL RUN-UP AND TAXI TO RWY 19L AT SNA; WE WERE GIVEN A CLRNC TO TAKE OFF. I WAS THE PF. DURING THE TKOF RUN; ALL ENG INSTS INDICATED NORMAL AND INITIAL ROTATION AND TKOF WAS NORMAL. AT APPROX 200 FT AGL; THERE WAS A MOMENTARY PWR LOSS OF ABOUT 80% FOR A SECOND; AFTER WHICH PWR RETURNED TO NORMAL. AT THIS POINT; BOTH MYSELF AND MY INSTRUCTOR VERIFIED FUEL SELECTOR WAS SET TO 'BOTH;' MIXTURE RICH; PROP CTL FULL; AND MAGNETOS/MASTER/PRIMER IN PROPER POS. SOON AFTER THIS; THE ENG STARTED SPUTTERING AND SEEMED TO ALMOST QUIT WHEN THROTTLE CTL WAS IN THE FULL OPEN POS. MY FLT INSTRUCTOR TOOK THE CTLS AT THIS POINT AND RADIOED TO TWR THAT WE HAD A ROUGH ENG AND WERE MAKING A R 180 DEG TURN TO RETURN TO LAND ON RWY 1L OR RWY 1R. TWR INSTRUCTED NOT TO TURN R; BUT TURN L TO DO THE 180 DEG TURN; AND WE COMPLIED SINCE WE WERE NOT AWARE OF WHAT TFC MIGHT BE ON APCH ON RWY 19R. IT SHOULD BE NOTED THAT RWY 19R IS A MUCH LONGER RWY THAN RWY 19L AND THAT IT IS USED BY NUMEROUS AIRLINERS AND CPR JETS. DURING THE L 180 DEG TURN; WE WERE AT 300-400 FT AGL AND THE ENG WAS STILL SPUTTERING. BY CHANGING THE THROTTLE POS; WE WERE ONLY ABLE TO DEVELOP ABOUT 20% PWR. AFTER THE 180 DEG TURN WE WERE VERY HIGH ON A SHORT FINAL TO RWY 1R WHEN MY FLT INSTRUCTOR PUT IN FULL FLAPS AND PUT THE ACFT INTO A SLIP. AT THIS POINT I SAW WE WOULD NOT TOUCH DOWN IN TIME TO STOP AT THE END OF THE RWY AND I DECLARED AN EMER TO TWR. 1/2 WAY DOWN THE RWY WE TOUCHED DOWN FAST AND BOUNCED; AFTER WHICH MY INSTRUCTOR ADDED PWR AND COMMENCED A GAR. FORTUNATELY; THE ENG WAS STILL DEVELOPING ENOUGH PWR TO CLB AND SHE RADIOED THE INTENTION TO DO A L 180 DEG TURN TO RWY 19R. I SAW THAT THE FLAPS WERE STILL AT 30 DEGS ON INITIAL CLB; SO I DREW THAT TO HER ATTN AND RETRACTED THEM TO 20 DEGS IN ORDER TO GET RID OF DRAG. DURING THE SECOND 280 DEG TURN; OUR L TURN GOT VERY STEEP AND SLOW AND I YELLED 'WATCH OUT FOR STALL SPIN!' TWICE TO WHICH SHE SAID THANK YOU AND LESSENED THE BANK. AFTER THE TURN; WE WERE LINED UP CORRECTLY FOR RWY 19R AND SHE PERFORMED A NORMAL LNDG. IN RETROSPECT; THERE WERE CERTAIN THINGS THAT I THINK COULD HAVE BEEN DONE DIFFERENTLY IN THIS SIT. ON THE POSITIVE NOTE; IDENT OF THE PROB WAS QUICK AND DELIBERATE. HOWEVER; GIVEN A SLIGHT TAILWIND ON THE DOWNWIND LNDG AND OUR PROB; WE SHOULD HAVE ATTEMPTED THE LONGER RWY 1L INSTEAD OF RWY 1R. WHILE MY INSTRUCTOR WAS CTLING THE AIRPLANE; I COULD HAVE DECLARED THE EMER SOONER AND COMMUNICATED THAT WE NEED RWY 1L. ALSO; THE FACT THAT WE WERE TOO HIGH AFTER THE FIRST 180 DEGS TO MAKE A SAFE LNDG ON THE RWY MEANS THAT WE SHOULD HAVE MANAGED THE EXCESSIVE ENERGY BETTER BY GETTING THE FLAPS DOWN EARLIER; DOING S-TURN; AND/OR SLIPPING SOONER SO THAT WE WOULD HAVE GOT RID OF OUR ALT SOONER TO MAKE A LNDG WITHIN THE ALLOTTED RWY. AS MY INSTRUCTOR; THE CHIEF PLT AT THE SCHOOL; AND MYSELF HAVE DISCUSSED; WE HAVE ALL AGREED THAT THE DECISION TO MAKE A GAR AFTER ALREADY TOUCHING DOWN WAS THE WRONG ONE. ALTHOUGH THE ENG WAS DEVELOPING PWR; THERE WAS NO GUARANTEE THAT IT WOULD NOT HAVE QUIT IMMEDIATELY AFTER THE GAR COMMENCED. CONTINUING THE ROLLOUT WOULD HAVE RESULTED IN THE AIRPLANE ROLLING OFF THE END OF THE RWY INTO THE DIRT WHICH MOST LIKELY WOULD HAVE DAMAGED THE PLANE SIGNIFICANTLY; BUT WOULD NOT HAVE RESULTED IN FORCES THAT WOULD HAVE CAUSED SERIOUS INJURY TO OURSELVES. IF THE ENG WERE TO QUIT AFTER THE LIFTOFF; WE WOULD NOT HAVE BEEN ABLE TO COMPLETE THE 180 DEG TURN AND WOULD HAVE BEEN FORCED TO LAND ON THE 405 FREEWAY WHICH WAS VERY BUSY; OR IN THE DENSELY POPULATED AREA AROUND THE ARPT. THIS DECISION; ALTHOUGH IT TURNED OUT FOR THE BEST; JEOPARDIZED THE LIVES OF BOTH US AND THOSE ON THE GND. IN THE RETROSPECT; A PARTIAL PWR LOSS CAUSES A GREAT DEAL OF JUDGEMENT CALLS AND DECISIONS THAT MUSTBE MADE. THE FACT THAT THE ENG IS STILL DEVELOPING SOME PWR MAY TEMPT PLTS TO ATTEMPT SOME MANEUVERS THAT ARE NOT SAFE IF THE ENG WERE TO COMPLETELY QUIT. PLTS NEED TO DECISIVELY IDENT THAT THIS TYPE SIT IS A REAL EMER AND DO WHAT IT TAKES TO GET THE ACFT ON THE GND SAFELY ASAP.