A C172 PLT ADDS OIL TO THE ACFT BUT FAILS TO SECURE THE OIL CAP RESULTING IN OIL ESCAPING DOWN THE SIDE OF THE ACFT.

Narrative

I WAS PREFLTING AN ACFT IN PREPARATION FOR GIVING AIRPLANE RIDES FOR A FRIEND'S GRADUATION PARTY. UPON CHKING THE OIL; I NOTICED THE OIL WAS A QUART LOW; SO I GOT A BOTTLE AND ADDED IT. THE ACFT WAS AN OLDER C172; WITH A SEPARATE DIPSTICK AND FILLER CAP. AFTER ADDING THE OIL; I CHKED TO SEE THAT THE DIPSTICK WAS SECURE; BUT MISSED PROPERLY SECURING THE FILLER CAP. ANOTHER PLT TOOK MY PLACE FOR THE FIRST FLT; AND ALSO MISSED THE CAP. WHEN HE CAME BACK AFTER THE PLANNED 10-MIN FLT; THERE WAS A LARGE BROWNISH STREAK ON THE SIDE AND BELLY OF THE ACFT. IT WAS THEN THAT THE LOOSE CAP WAS DISCOVERED; AND I REALIZED MY ERROR. FORTUNATELY; NO ONE WAS HURT; AND ALL THAT WAS LEFT WERE SOME BITTER RECRIMINATIONS FROM MY FRIEND AND THE OTHER PLT; WHO ALSO FELT UPSET FOR MISSING THE CAP HIMSELF; PLUS CLEANING OFF A DIRTY ACFT. FROM THIS; I HAVE LEARNED TO PAY CLOSER ATTN TO MY PREFLTS; WITH SPECIAL EMPHASIS ON CHKING NOT ONLY THE SECURITY OF THE OIL DIPSTICK; BUT ALSO THE FILLER CAP; WHETHER OR NOT I ADD ANY OIL.