Narrative:

I departed fdk about XZ30 on an IFR flight plan to anp on runway 5 on a vector to EMI VOR, level at 3000 ft MSL with pct approach. The controller advised I had merged with another target and a shadow flashed across me. I did not see or hear another aircraft. I estimate he was slightly above and to the rear of me. I was then vectored to 10 mi from anp where I canceled IFR and landed.

Google
 

Original NASA ASRS Text

Title: PLT OF M20P EXPERIENCES NEAR MISS WITH UNIDENTED ACFT WHILE OPERATING ON IFR FLT PLAN NEAR FDK.

Narrative: I DEPARTED FDK ABOUT XZ30 ON AN IFR FLT PLAN TO ANP ON RWY 5 ON A VECTOR TO EMI VOR, LEVEL AT 3000 FT MSL WITH PCT APCH. THE CTLR ADVISED I HAD MERGED WITH ANOTHER TARGET AND A SHADOW FLASHED ACROSS ME. I DID NOT SEE OR HEAR ANOTHER ACFT. I ESTIMATE HE WAS SLIGHTLY ABOVE AND TO THE REAR OF ME. I WAS THEN VECTORED TO 10 MI FROM ANP WHERE I CANCELED IFR AND LANDED.

Data retrieved from NASA's ASRS site as of July 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.