C150 PLT ENTERING TFC PATTERN AT NON TWR ARPT HAS NMAC WITH ACFT TRANSITING THE AREA AND NOT BROADCASTING ON THE CTAF.

Narrative

MY WIFE AND I WERE ON OUR WAY BACK TO PTW FROM CHESTER COUNTY; PA; AFTER A PLEASANT MORNING FLT AND NICE BREAKFAST AT THE ARPT DINER. IT WASN'T A PERFECT SATURDAY FOR FLYING; A BIT HAZY; BUT STILL OVER 12 MI VISIBILITY. AT 5 MI OUT; I WAS ABLE TO GET IN A QUICK CALL TO LIMERICK FOR AN ARPT ADVISORY AND THEN; A COUPLE MINS LATER; A CALL TO ANNOUNCE THAT WE WERE 2 MI S OF THE ARPT. LIMERICK ITSELF WASN'T VERY BUSY WITH JUST 1 HIGH WING TAKING OFF AND HDG W. I KEPT AN EYE ON HIM TO MAKE SURE HE KEPT GOING W AND DIDN'T DECIDE TO MAKE A TURN INTO THE R-HAND PATTERN THAT'S STANDARD FOR RWY 28 AT LIMERICK. I ALSO LOOKED FOR OTHER TFC ALONG THE DOWNWIND LEG THAT MIGHT INTERFERE WITH OUR ENTRANCE INTO THE PATTERN AND WHO MIGHT NOT HAVE A RADIO; OR HAD FAILED TO MAKE USE OF THE ONE THEY DID HAVE. EVERYTHING LOOKED CLR. I THEN ANNOUNCED THAT WE WERE OVER THE FIELD AT 1400 FT TO ENTER A DOWNWIND FOR RWY 28 AT THE MIDPOINT. JUST AFTER XING OVER THE RWY; I LOOKED DOWN TO CHK THE WINDSOCK ON THE LIMERICK HANGAR AND GAUGE ANY XWIND I'D HAVE TO DEAL WITH ON FINAL APCH. WHILE I LOOKED FOR THE WINDSOCK; I NOTICED THE SHADOW OF OUR C150 GLIDING PEACEFULLY OVER THE LANDSCAPE BELOW. THEN; IN AN INSTANT; THAT PEACEFUL VIEW WAS SHATTERED AND WAS REPLACED BY AN IMAGE OF IMPENDING DISASTER. THE SHADOW OF OUR AIRPLANE WASN'T THE ONLY SHADOW ON THE GND. THE SHADOW OF ANOTHER AIRPLANE; A SHADOW OF ABOUT THE SAME SIZE; WAS OFF OUR STARBOARD WING AND WAS CONVERGING ON OUR SHADOW AT A 90 DEG ANGLE WITH ONLY SECONDS TO GO. I STARED AT THE SHADOWS WITH A FEELING OF DETACHED DISBELIEF. I NEEDED TO DO SOMETHING BUT THERE WAS NO DECISION I COULD MAKE. BASED ON THE SHADOWS ALONE; THERE WAS NO WAY TO KNOW IF THE OTHER PLANE WAS SLIGHTLY ABOVE; SLIGHTLY BELOW; OR EXACTLY AT OUR ALT. EVERY ACTION THAT RACED THROUGH MY MIND IN THAT MOMENT OF TIME SEEMED TO HAVE AN EQUAL CHANCE OF MAKING THINGS WORSE AS IT DID BETTER. AFTER WHAT SEEMED LIKE FOREVER; BUT WAS MORE LIKE 2 SECONDS; I QUICKLY TURNED MY HEAD TO THE R JUST IN TIME TO WATCH THE WING OF A C182 SLIDE UNDER THE TAIL OF OUR PLANE NO MORE THAN 20 FT BELOW US. IT WAS A CHILLING SIGHT. I QUICKLY LOOKED BACK TO THE L AND VISUALLY FOLLOWED THE PLANE AS IT CONTINUED ON ITS WESTWARD HDG. IT WAS AN 'ENRTE' ACFT; NOT INTERESTED IN LNDG AT LIMERICK. THE SHOCK EFFECT OF THE NEAR MISS KEPT ME FROM NOTING THE TAIL NUMBER OF THE OTHER PLANE UNTIL IT WAS TOO FAR AWAY TO READ THE REGISTRY. MY FEELING OF DISBELIEF GAVE WAY TO A FEELING OF NUMBNESS. I FORCED MYSELF TO PUT THE INCIDENT ASIDE LONG ENOUGH TO GET ON WITH THE BUSINESS OF LNDG THE PLANE. I PROCEEDED TO TURN THE PLANE ONTO THE DOWNWIND LEG AND WE COMPLETED THE PATTERN AND LANDED WITHOUT FURTHER INCIDENT. AS WE TAXIED BACK TO OUR TIE-DOWN; MY WIFE AND I LET OUT A COLLECTIVE EXHALE THAT; WITHOUT WORDS; SAID WE KNEW WE HAD BEEN VERY LUCKY. HAD I SEEN HIM EARLY ENOUGH I WOULD HAVE TAKEN ACTION TO AVOID THE NEAR MISS; REGARDLESS OF RIGHT-OF-WAY; BUT BY THE TIME I SAW HIM THERE WAS NO TIME TO DO ANYTHING. FAR 91.127(C) STATES THIS GENERAL RULE: 'NO ACFT SHALL OPERATE IN AN ATA EXCEPT FOR THE PURPOSE OF LNDG AND DEPARTING THAT ARPT.' THIS IS THE REG I FLY BY IN THE VICINITY OF ARPTS AND I GENERALLY ASSUME OTHER PLTS TO BE DOING THE SAME. NEEDLESS TO SAY; I WON'T BE ASSUMING THAT ANY MORE.