Narrative:

On a clear hazy day with the sun to our backs we were being vectored for an approach to 22L at ewr. We were heading 010 degree at 6000' MSL. Approach advised us of converging IFR traffic (small aircraft) at 10 O'clock 5000' nebnd. After several checks in that position I finally spotted him maybe 10 seconds before he passed beneath us. I wasn't especially busy at the time, and I just watched him lazily drift beneath us. When I looked up again I saw the small cross section and very bright landing light of a jet fighter aircraft at exactly 12 O'clock at very close range at our altitude. Many things happened, both mentally and physically during the next second and a half! I overrode the autoplt and pushed the nose over sharply. As I was pulling back the thrust levers and cursing loudly, the fighter turned into a silver mylar balloon with a blue ribbon hanging from it! I could see what it was when it zipped just over our heads and the sunlight no longer reflected directly back in my eyes (the landing light). I was convinced it was a military fighter, complete with the usual trail of dark smoke coming out the back (the blue ribbon?). Then I remembered the traffic directly below us!! I pulled the nose up just as sharply as before. Fortunately everyone was seated in the back, and there were no injuries or damage except for our nerves and some spilled coffee. I still can't believe how real the illusion was. Our total altitude deviation was no more than 200'.

Google
 

Original NASA ASRS Text

Title: BALLOON IDENTIFIED AS AN FGT TYPE ACFT AND SUDDEN EVASIVE ACTION TAKEN.

Narrative: ON A CLEAR HAZY DAY WITH THE SUN TO OUR BACKS WE WERE BEING VECTORED FOR AN APCH TO 22L AT EWR. WE WERE HDG 010 DEG AT 6000' MSL. APCH ADVISED US OF CONVERGING IFR TFC (SMA) AT 10 O'CLOCK 5000' NEBND. AFTER SEVERAL CHECKS IN THAT POSITION I FINALLY SPOTTED HIM MAYBE 10 SECONDS BEFORE HE PASSED BENEATH US. I WASN'T ESPECIALLY BUSY AT THE TIME, AND I JUST WATCHED HIM LAZILY DRIFT BENEATH US. WHEN I LOOKED UP AGAIN I SAW THE SMALL CROSS SECTION AND VERY BRIGHT LNDG LIGHT OF A JET FIGHTER ACFT AT EXACTLY 12 O'CLOCK AT VERY CLOSE RANGE AT OUR ALT. MANY THINGS HAPPENED, BOTH MENTALLY AND PHYSICALLY DURING THE NEXT SECOND AND A HALF! I OVERRODE THE AUTOPLT AND PUSHED THE NOSE OVER SHARPLY. AS I WAS PULLING BACK THE THRUST LEVERS AND CURSING LOUDLY, THE FIGHTER TURNED INTO A SILVER MYLAR BALLOON WITH A BLUE RIBBON HANGING FROM IT! I COULD SEE WHAT IT WAS WHEN IT ZIPPED JUST OVER OUR HEADS AND THE SUNLIGHT NO LONGER REFLECTED DIRECTLY BACK IN MY EYES (THE LNDG LIGHT). I WAS CONVINCED IT WAS A MIL FIGHTER, COMPLETE WITH THE USUAL TRAIL OF DARK SMOKE COMING OUT THE BACK (THE BLUE RIBBON?). THEN I REMEMBERED THE TFC DIRECTLY BELOW US!! I PULLED THE NOSE UP JUST AS SHARPLY AS BEFORE. FORTUNATELY EVERYONE WAS SEATED IN THE BACK, AND THERE WERE NO INJURIES OR DAMAGE EXCEPT FOR OUR NERVES AND SOME SPILLED COFFEE. I STILL CAN'T BELIEVE HOW REAL THE ILLUSION WAS. OUR TOTAL ALT DEVIATION WAS NO MORE THAN 200'.

Data retrieved from NASA's ASRS site as of August 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.