Narrative:

I was acting as captain on this flight. We were being vectored by ZAU in an area of thunderstorms to proceed eventually over pontiac for an approach to runway 9R. The frequency in use was saturated with requests for deviation and there was extensive complaining by several aircraft to the controller's instructions. We were cleared to descend from above FL180 to 16000 ft. No altimeter setting for the champaign area was given passing FL180. I called for descent check. The first officer had copied the ATIS and called out 30.49 which we set in both altimeters. After leveling at 16000 ft, ZAU asked what altitude we were at. After replying 'level at 16000 ft,' center replied, 'I show you at 15500 ft, check altimeter setting 29.46, maintain 16000 ft.' I immediately initiated corrective action to level at 16000 ft after changing the altimeter setting. To my knowledge there was no conflict with other traffic or compromise with safety. In reviewing the occurrence with the first officer, he stated that the ATIS was difficult to understand and breaking up with static due to lightning in the area. I believe this factor, coupled with the high stress of the situation for both the controller and us, accounted for this deviation. To prevent recurrence of this situation, controllers should make a point of including the local altimeter setting for any clearance below FL180. Pilots should make a point of not accepting a clearance below FL180 without receiving the local altimeter setting from the controller and then xchk that setting with what is being advertised on the ATIS.

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Original NASA ASRS Text

Title: POOR WX, LARGE VOLUME OF TFC AND CONGESTED ATC FREQS WHEN RPTR ACFT WAS CLRED FROM ABOVE FL180 TO 16000 FT. CTLR DID NOT PROVIDE A LCL ALTIMETER SETTING, BUT FLC THOUGHT THEY HAD PICKED IT UP ON ATIS, WHICH WAS DIFFICULT TO HEAR DUE TO STATIC CAUSED BY LIGHTNING IN THE AREA. CTR CTLR QUESTIONED THEIR ALT WHEN THEY WERE SUPPOSED TO BE LEVEL AT 16000 FT AND THEN THEY REALIZED THEY HAD AN ERRONEOUS ALTIMETER SETTING.

Narrative: I WAS ACTING AS CAPT ON THIS FLT. WE WERE BEING VECTORED BY ZAU IN AN AREA OF TSTMS TO PROCEED EVENTUALLY OVER PONTIAC FOR AN APCH TO RWY 9R. THE FREQ IN USE WAS SATURATED WITH REQUESTS FOR DEV AND THERE WAS EXTENSIVE COMPLAINING BY SEVERAL ACFT TO THE CTLR'S INSTRUCTIONS. WE WERE CLRED TO DSND FROM ABOVE FL180 TO 16000 FT. NO ALTIMETER SETTING FOR THE CHAMPAIGN AREA WAS GIVEN PASSING FL180. I CALLED FOR DSCNT CHK. THE FO HAD COPIED THE ATIS AND CALLED OUT 30.49 WHICH WE SET IN BOTH ALTIMETERS. AFTER LEVELING AT 16000 FT, ZAU ASKED WHAT ALT WE WERE AT. AFTER REPLYING 'LEVEL AT 16000 FT,' CTR REPLIED, 'I SHOW YOU AT 15500 FT, CHK ALTIMETER SETTING 29.46, MAINTAIN 16000 FT.' I IMMEDIATELY INITIATED CORRECTIVE ACTION TO LEVEL AT 16000 FT AFTER CHANGING THE ALTIMETER SETTING. TO MY KNOWLEDGE THERE WAS NO CONFLICT WITH OTHER TFC OR COMPROMISE WITH SAFETY. IN REVIEWING THE OCCURRENCE WITH THE FO, HE STATED THAT THE ATIS WAS DIFFICULT TO UNDERSTAND AND BREAKING UP WITH STATIC DUE TO LIGHTNING IN THE AREA. I BELIEVE THIS FACTOR, COUPLED WITH THE HIGH STRESS OF THE SIT FOR BOTH THE CTLR AND US, ACCOUNTED FOR THIS DEV. TO PREVENT RECURRENCE OF THIS SIT, CTLRS SHOULD MAKE A POINT OF INCLUDING THE LCL ALTIMETER SETTING FOR ANY CLRNC BELOW FL180. PLTS SHOULD MAKE A POINT OF NOT ACCEPTING A CLRNC BELOW FL180 WITHOUT RECEIVING THE LCL ALTIMETER SETTING FROM THE CTLR AND THEN XCHK THAT SETTING WITH WHAT IS BEING ADVERTISED ON THE ATIS.

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.