Narrative:

During vectors to ILS runway 4R approach at mdw, I received a clearance which contained, 'descend and maintain 2000 ft till established, maintain 180 KTS or greater to the marker. Contact tower 118.7. Cleared ILS runway 4R.' mins later tower asked us to return to approach. The controller asked, 'what are you doing at 2000 ft?' I responded, 'that was the altitude we were assigned and read back.' the controller responded, 'the intercept altitude is 2600 ft.' I reported level at 2600 ft moments later and changed to tower 118.7 at the marker. No TCASII or GPWS alerts were generated. In my judgment, this miscom occurred due to multiple factors. The speed or rapidity of the approach clearance and the large number of elements made it difficult to receive. Also, I did not clarify each element of the clearance, as the frequency was congested and the pace rapid. My copilot and I still believe we were cleared to 2000 ft, but the complexity of the clearance may also have contributed to our aircraft being 600 ft low on the localizer to runway 4R before correcting to 2600 ft for GS intercept.

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Original NASA ASRS Text

Title: HS125 FLT CREW IS QUESTIONED BY ATC REGARDING INTERCEPT ALT ON ILS FOR MDW.

Narrative: DURING VECTORS TO ILS RWY 4R APCH AT MDW, I RECEIVED A CLRNC WHICH CONTAINED, 'DSND AND MAINTAIN 2000 FT TILL ESTABLISHED, MAINTAIN 180 KTS OR GREATER TO THE MARKER. CONTACT TWR 118.7. CLRED ILS RWY 4R.' MINS LATER TWR ASKED US TO RETURN TO APCH. THE CTLR ASKED, 'WHAT ARE YOU DOING AT 2000 FT?' I RESPONDED, 'THAT WAS THE ALT WE WERE ASSIGNED AND READ BACK.' THE CTLR RESPONDED, 'THE INTERCEPT ALT IS 2600 FT.' I RPTED LEVEL AT 2600 FT MOMENTS LATER AND CHANGED TO TWR 118.7 AT THE MARKER. NO TCASII OR GPWS ALERTS WERE GENERATED. IN MY JUDGMENT, THIS MISCOM OCCURRED DUE TO MULTIPLE FACTORS. THE SPD OR RAPIDITY OF THE APCH CLRNC AND THE LARGE NUMBER OF ELEMENTS MADE IT DIFFICULT TO RECEIVE. ALSO, I DID NOT CLARIFY EACH ELEMENT OF THE CLRNC, AS THE FREQ WAS CONGESTED AND THE PACE RAPID. MY COPLT AND I STILL BELIEVE WE WERE CLRED TO 2000 FT, BUT THE COMPLEXITY OF THE CLRNC MAY ALSO HAVE CONTRIBUTED TO OUR ACFT BEING 600 FT LOW ON THE LOC TO RWY 4R BEFORE CORRECTING TO 2600 FT FOR GS INTERCEPT.

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.