Narrative:

There were large thunderstorms just west and north of airport. Just after takeoff, at approximately 500 ft AGL, our radar stopped working. We advised dayton departure of our predicament and we suggested that they give us vectors to follow a B-767 that departed just before us. During our subsequent climb to FL350, we encountered various levels of turbulence due to convective WX. A few weeks later, we received a call from the FAA that we had descended from 28600 ft to 28200 ft while climbing to FL350. The indy controller had not mentioned anything to us during the flight, but apparently there was a loss of separation. Contributing factors may include: 1) poor aircraft performance due to anti-ice climb confign, density altitude, etc, 2) turbulence WX/flight conditions due to thunderstorm, 3) loss of WX radar, 4) pilot fatigue (night flying), 5) ATC not passing along information that our radar was OTS to the next controller, 6) complacency -- pilots not advising ATC of altitude deviation (however neither the first officer or myself remember losing this much altitude), and 7) aging aircraft (falcon 20) with tired engines. We sent a statement to the FAA regarding the event that night, however, we only recall bits and pieces since we were not immediately told of this altitude incident. We learned of this weeks later.

Related reports:

Google
 

Original NASA ASRS Text

Title: FA20 CREW WAS NOTIFIED THAT THEY HAD AN ALTDEV SEVERAL WKS AFTER THE INCIDENT IN ZID CLASS A.

Narrative: THERE WERE LARGE TSTMS JUST W AND N OF ARPT. JUST AFTER TKOF, AT APPROX 500 FT AGL, OUR RADAR STOPPED WORKING. WE ADVISED DAYTON DEP OF OUR PREDICAMENT AND WE SUGGESTED THAT THEY GIVE US VECTORS TO FOLLOW A B-767 THAT DEPARTED JUST BEFORE US. DURING OUR SUBSEQUENT CLB TO FL350, WE ENCOUNTERED VARIOUS LEVELS OF TURB DUE TO CONVECTIVE WX. A FEW WKS LATER, WE RECEIVED A CALL FROM THE FAA THAT WE HAD DSNDED FROM 28600 FT TO 28200 FT WHILE CLBING TO FL350. THE INDY CTLR HAD NOT MENTIONED ANYTHING TO US DURING THE FLT, BUT APPARENTLY THERE WAS A LOSS OF SEPARATION. CONTRIBUTING FACTORS MAY INCLUDE: 1) POOR ACFT PERFORMANCE DUE TO ANTI-ICE CLB CONFIGN, DENSITY ALT, ETC, 2) TURB WX/FLT CONDITIONS DUE TO TSTM, 3) LOSS OF WX RADAR, 4) PLT FATIGUE (NIGHT FLYING), 5) ATC NOT PASSING ALONG INFO THAT OUR RADAR WAS OTS TO THE NEXT CTLR, 6) COMPLACENCY -- PLTS NOT ADVISING ATC OF ALTDEV (HOWEVER NEITHER THE FO OR MYSELF REMEMBER LOSING THIS MUCH ALT), AND 7) AGING ACFT (FALCON 20) WITH TIRED ENGS. WE SENT A STATEMENT TO THE FAA REGARDING THE EVENT THAT NIGHT, HOWEVER, WE ONLY RECALL BITS AND PIECES SINCE WE WERE NOT IMMEDIATELY TOLD OF THIS ALT INCIDENT. WE LEARNED OF THIS WKS LATER.

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.