PLT INST TRNEE RETURNED TO LAND AFTER TKOF DUE TO WHAT APPEARED TO BE AN ENG FIRE DURING THE START OF A NIGHT INST TRAINING FLT.

Narrative

THE FLT WAS IN A TWIN ENG BE-76 LEAVING ADDISON FOR LCL IFR TRAINING AT NIGHT. ACFT PERFORMANCE THROUGH TKOF AND CLB WAS NORMAL. AS THE TKOF PROGRESSED THROUGH ABOUT 200 FT AGL; I HAPPENED TO GLANCE OUT MY L WINDOW AT THE L ENG. I WAS COMPLETELY SURPRISED TO SEE THE BOTTOM OF THE ENG COWLING WREATHED IN A BLUE FLAME. I NOTIFIED TWR THAT WE HAD A POSSIBLE ENG FIRE AND THAT WE WERE RETURNING TO LAND. TWR ASKED IF WE NEEDED THE EQUIP; I DECLINED AS AT THIS POINT; PWR HAD BEEN REDUCED AND MOST OF THE FLAME HAD DISSIPATED. AN UNEVENTFUL LNDG FOLLOWED. POST-FLT INVESTIGATION SHOWED NO SIGNS OF FIRE. UPON CONSULTING SEVERAL OTHER PLTS AND AN A&P; IT WAS DETERMINED THAT THIS WAS IN FACT NORMAL BEHAVIOR FOR THE ACFT. UNDER CERTAIN ATMOSPHERIC AND ENG CONDITIONS; THE ENGS CAN PRODUCE QUITE A BIT OF FLAME. HOWEVER; NOWHERE IN THE PLT OPERATING HANDBOOK OR IN MY TRAINING; OR IN MY STUDY; WAS I EVER TOLD TO EXPECT FLAME FROM A 180 HP ENG. IN MY CASE; THE RESULT WAS 2 MINS OF TERROR AND A LITTLE EMBARRASSMENT. HOWEVER; HAD THE WX BEEN WORSE; OR HAD I ELECTED TO SECURE THE ENG; THE OUTCOME MIGHT NOT HAVE BEEN SO HAPPY. I CONSIDER MYSELF TO BE A COMPETENT PLT. I HAD FLOWN THE ACFT MANY TIMES AT NIGHT; BUT HAD NEVER SEEN THIS PHENOMENA; WHICH TURNS OUT TO BE QUITE COMMON. THIS WHOLE INCIDENT COULD HAVE BEEN AVOIDED IF SOMEONE; BE IT BEECHCRAFT; A CFI; OR AN FAA AC ON FLYING TWINS HAD BOTHERED TO TELL ME TO EXPECT THIS COMMON; RATHER UNNERVING PHENOMENA.