Narrative:

While making a flight from memphis, tn to moline, il, we entered a thunderstorm and had altitude deviations of +/-1000'. We were cruising at FL310 on J35 heading north toward farmington VOR. It was around 10 O'clock at night. There were reports of level 1, 2 and 3 thunderstorms along our route, which I could confirm visually by the flashes of lightning below. I was making periodic adjustments to the radar trying to obtain a return that would show some level of precipitation. At approximately 8 mi from the thunderstorm, ATC advised us of a storm ahead and asked us to advise him which way we would turn. Again I made adjustments to the radar trying to obtain a return so that we could plan a course around the thunderstorm. In less than 1 min we entered a cloud. Then the up and downdrafts began. I disconnected the autoplt, started a turn, advised ATC of our situation and asked for a vector out of and around the thunderstorm. In retrospect, I would have liked to have seen the situation handled differently. First, I wish I had discovered that the radar was unreliable sooner. Secondly, I had told ATC that our radar was not working properly and would need assistance. Third, ATC could have informed us prior to just 8 mi that there was a thunderstorm ahead. Supplemental information from acn 164105: shortly after takeoff we discovered that our airborne radar was unreliable. Since thunderstorm activity did exist along our route, ATC should have been made aware of our radar problem long before they were. Our radar unreliability was not made known to ATC until the aircraft was within 8 mi of a line of thunderstorms.

Related reports:

Google
 

Original NASA ASRS Text

Title: CHARTER LTT ALT DEVIATION EXCURSION FROM CLRNC ALT IN TSTM ACTIVITY.

Narrative: WHILE MAKING A FLT FROM MEMPHIS, TN TO MOLINE, IL, WE ENTERED A TSTM AND HAD ALT DEVIATIONS OF +/-1000'. WE WERE CRUISING AT FL310 ON J35 HDG N TOWARD FARMINGTON VOR. IT WAS AROUND 10 O'CLOCK AT NIGHT. THERE WERE RPTS OF LEVEL 1, 2 AND 3 TSTMS ALONG OUR RTE, WHICH I COULD CONFIRM VISUALLY BY THE FLASHES OF LIGHTNING BELOW. I WAS MAKING PERIODIC ADJUSTMENTS TO THE RADAR TRYING TO OBTAIN A RETURN THAT WOULD SHOW SOME LEVEL OF PRECIPITATION. AT APPROX 8 MI FROM THE TSTM, ATC ADVISED US OF A STORM AHEAD AND ASKED US TO ADVISE HIM WHICH WAY WE WOULD TURN. AGAIN I MADE ADJUSTMENTS TO THE RADAR TRYING TO OBTAIN A RETURN SO THAT WE COULD PLAN A COURSE AROUND THE TSTM. IN LESS THAN 1 MIN WE ENTERED A CLOUD. THEN THE UP AND DOWNDRAFTS BEGAN. I DISCONNECTED THE AUTOPLT, STARTED A TURN, ADVISED ATC OF OUR SITUATION AND ASKED FOR A VECTOR OUT OF AND AROUND THE TSTM. IN RETROSPECT, I WOULD HAVE LIKED TO HAVE SEEN THE SITUATION HANDLED DIFFERENTLY. FIRST, I WISH I HAD DISCOVERED THAT THE RADAR WAS UNRELIABLE SOONER. SECONDLY, I HAD TOLD ATC THAT OUR RADAR WAS NOT WORKING PROPERLY AND WOULD NEED ASSISTANCE. THIRD, ATC COULD HAVE INFORMED US PRIOR TO JUST 8 MI THAT THERE WAS A TSTM AHEAD. SUPPLEMENTAL INFO FROM ACN 164105: SHORTLY AFTER TKOF WE DISCOVERED THAT OUR AIRBORNE RADAR WAS UNRELIABLE. SINCE TSTM ACTIVITY DID EXIST ALONG OUR RTE, ATC SHOULD HAVE BEEN MADE AWARE OF OUR RADAR PROB LONG BEFORE THEY WERE. OUR RADAR UNRELIABILITY WAS NOT MADE KNOWN TO ATC UNTIL THE ACFT WAS WITHIN 8 MI OF A LINE OF TSTMS.

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.