Narrative:

IFR from C93 to dpa. Thick haze entire route. We arrived at dpa VOR, via V171, from rfd. ATC gave a heading of 030 degrees, to intercept the ILS 1L localizer. Shortly after turning to 030 degrees, sky ahead of aircraft appeared to be darkening quickly. I advised ATC that I could not continue further east, due to building WX. I requested a turn to the south, to avoid the buildup. Controller advised 'you are on top of the localizer now. If I vector you south, you'll just have to come through the area again.' CDI in the aircraft still showed a full deflection with aircraft west of the localizer. I told the controller 'ok, just give us the quickest way down.' (in retrospect, the double entendre here is chilling). We were told to maintain 2800 ft until established and fly heading 030 degrees. Moments after this, aircraft entered heavy rain, and downdrafts. Even at full power, I lost 400 ft before we exited the cell. Localizer and GS were intercepted without incident, remainder of flight uneventful. Points to note: 1) I was PIC, not the controller. I should have insisted on vectors away from the buildup. 2) controller's radar is not as accurate as aircraft CDI. Even though controller thought I was above the localizer, I knew I was not there yet, and would have to proceed further into adverse WX.

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Original NASA ASRS Text

Title: SMA PLT SIGHTS OMINOUS WX AHEAD WHEN INTERCEPTING THE LOC. HE REQUESTS A TURN TO THE S, BUT CTLR INDICATES HE WILL ONLY HAVE TO COME BACK INTO THE WX. PROCEEDING AHEAD RPTR ENCOUNTERS SEVERE DOWNDRAFT.

Narrative: IFR FROM C93 TO DPA. THICK HAZE ENTIRE RTE. WE ARRIVED AT DPA VOR, VIA V171, FROM RFD. ATC GAVE A HDG OF 030 DEGS, TO INTERCEPT THE ILS 1L LOC. SHORTLY AFTER TURNING TO 030 DEGS, SKY AHEAD OF ACFT APPEARED TO BE DARKENING QUICKLY. I ADVISED ATC THAT I COULD NOT CONTINUE FURTHER E, DUE TO BUILDING WX. I REQUESTED A TURN TO THE S, TO AVOID THE BUILDUP. CTLR ADVISED 'YOU ARE ON TOP OF THE LOC NOW. IF I VECTOR YOU S, YOU'LL JUST HAVE TO COME THROUGH THE AREA AGAIN.' CDI IN THE ACFT STILL SHOWED A FULL DEFLECTION WITH ACFT W OF THE LOC. I TOLD THE CTLR 'OK, JUST GIVE US THE QUICKEST WAY DOWN.' (IN RETROSPECT, THE DOUBLE ENTENDRE HERE IS CHILLING). WE WERE TOLD TO MAINTAIN 2800 FT UNTIL ESTABLISHED AND FLY HDG 030 DEGS. MOMENTS AFTER THIS, ACFT ENTERED HVY RAIN, AND DOWNDRAFTS. EVEN AT FULL PWR, I LOST 400 FT BEFORE WE EXITED THE CELL. LOC AND GS WERE INTERCEPTED WITHOUT INCIDENT, REMAINDER OF FLT UNEVENTFUL. POINTS TO NOTE: 1) I WAS PIC, NOT THE CTLR. I SHOULD HAVE INSISTED ON VECTORS AWAY FROM THE BUILDUP. 2) CTLR'S RADAR IS NOT AS ACCURATE AS ACFT CDI. EVEN THOUGH CTLR THOUGHT I WAS ABOVE THE LOC, I KNEW I WAS NOT THERE YET, AND WOULD HAVE TO PROCEED FURTHER INTO ADVERSE WX.

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.